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New research – Climate sensitivity, forcings, and feedbacks (August 8, 2016)

Posted by Ari Jokimäki on August 8, 2016

Some of the latest papers on climate sensitivity, forcings, and feedbacks are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


The Spectral Signature of Recent Climate Change (Brindley & Bantges, 2016)

Abstract: Spectrally resolved measurements of the Earth’s reflected shortwave (RSW) and outgoing longwave radiation (OLR) at the top of the atmosphere intrinsically contain the imprints of a multitude of climate relevant parameters. Here, we review the progress made in directly using such observations to diagnose and attribute change within the Earth system over the past four decades. We show how changes associated with perturbations such as increasing greenhouse gases are expected to be manifested across the spectrum and illustrate the enhanced discriminatory power that spectral resolution provides over broadband radiation measurements. Advances in formal detection and attribution techniques and in the design of climate model evaluation exercises employing spectrally resolved data are highlighted. We illustrate how spectral observations have been used to provide insight into key climate feedback processes and quantify multi-year variability but also indicate potential barriers to further progress. Suggestions for future research priorities in this area are provided.

Deep time evidence for climate sensitivity increase with warming (Shaffer et al. 2016)

Abstract: Future global warming from anthropogenic greenhouse gas emissions will depend on climate feedbacks, the effect of which is expressed by climate sensitivity, the warming for a doubling of atmospheric CO2 content. It is not clear how feedbacks, sensitivity, and temperature will evolve in our warming world, but past warming events may provide insight. Here we employ paleoreconstructions and new climate-carbon model simulations in a novel framework to explore a wide scenario range for the Paleocene-Eocene Thermal Maximum (PETM) carbon release and global warming event 55.8 Ma ago, a possible future warming analogue. We obtain constrained estimates of CO2 and climate sensitivity before and during the PETM and of the PETM carbon input amount and nature. Sensitivity increased from 3.3–5.6 to 3.7–6.5 K (Kelvin) into the PETM. When taken together with Last Glacial Maximum and modern estimates, this result indicates climate sensitivity increase with global warming.

Insights into Earth’s energy imbalance from multiple sources (Trenberth et al. 2016)

Abstract: The current Earth’s energy imbalance (EEI) can best be estimated from changes in ocean heat content (OHC), complemented by top-of-atmosphere (TOA) radiation measurements and an assessment of the small non-ocean components. Sustained observations from the Argo array of autonomous profiling floats enable near-global estimates of OHC since 2005, which reveal considerable cancellation of variations in the upper 300 m. An analysis of the monthly contributions to EEI from non-ocean (land and ice) using the CESM Large Ensemble reveals standard deviations of 0.3 to 0.4 W m-2 (global); largest values occur in August, but values are below 0.75 W m-2 >95% of the time. Global standard deviations of EEI of 0.64 W m-2 based on top-of-atmosphere observations therefore substantially constrain ocean contributions, given by the tendencies of OHC. Instead, monthly standard deviations of many Argo-based OHC tendencies are 6 to 13 W m-2 and non-physical fluctuations are clearly evident. We show that an ocean reanalysis with multi-variate dynamical data assimilation features much better agreement with TOA radiation, and 44% of the vertically-integrated short-term OHC trend for 2005-14 of 0.8±0.2 W m-2 (globally) occurs below 700 m depth. Largest warming occurs from 20 to 50°S, especially over the Southern Oceans, and near 40°N, in all ocean analyses. The EEI is estimated to be 0.9±0.3 W m-2 for 2005-2014.

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016)

Abstract: Although it is well-established that cirrus warms the Earth, the radiative effect of the entire spectrum of ice clouds is not well understood. In this study, the role of all ice clouds in the Earth’s radiation budget is investigated by performing radiative transfer modeling using ice cloud properties retrieved from CloudSat and CALIPSO measurements as inputs. Results show that, for the 2008 period, the warming effect (~21.8 ± 5.4 W m-2) induced by ice clouds due to trapping longwave radiation exceeds their cooling effect (~-16.7 ± 1.7 W m-2) caused by shortwave reflection, resulting in a net warming effect (~5.1 ± 3.8 W m-2) globally on the earth-atmosphere system. The net warming is over 15 W m-2 in the tropical deep convective regions, whereas cooling occurs in the midlatitudes, which is less than 10 W m-2 in magnitude. Seasonal variations of ice cloud radiative effects are evident in the midlatitudes where the net effect changes from warming during winter to cooling during summer, whereas warming occurs all year round in the tropics. Ice cloud optical depth (τ) is shown to be an important factor in determining the sign and magnitude of the net radiative effect. Ice clouds with τ < 4.6 display a warming effect with the largest contributions from those with τ ~ 1.0. In addition, ice clouds cause vertically differential heating and cooling of the atmosphere, particularly with strong heating in the upper troposphere over the tropics. At Earth’s surface, ice clouds produce a cooling effect no matter how small the τ value is.

Giant natural fluctuation models and anthropogenic warming (Lovejoy et al. 2016)

Abstract: Explanations for the industrial epoch warming are polarized around the hypotheses of anthropogenic warming (AW) and Giant Natural Fluctuations (GNF’s). While climate sceptics have systematically attacked AW, up until now they have only invoked GNF’s. This has now changed with the publication by D. Keenan of a sample of 1000 series from stochastic processes purporting to emulate the global annual temperature since 1880. While Keenan’s objective was to criticize the IPCC’s trend uncertainty analysis (their assumption that residuals are only weakly correlated), for the first time it is possible to compare a stochastic GNF model with real data. Using Haar fluctuations, probability distributions and other techniques of time series analysis, we show that his model has unrealistically strong low frequency variability so that even mild extrapolations imply ice ages every ≈ 1000 years. The GNF model can easily be scientifically rejected.

Other papers

Constraining the low-cloud optical depth feedback at middle and high latitudes using satellite observations (Terai et al. 2016)

Assessing the Radiative Effects of Global Ice Clouds Based on CloudSat and CALIPSO Measurements (Hong et al. 2016)

Which way will the circulation shift in a changing climate? Possible nonlinearity of extratropical cloud feedbacks (Tandon & Cane, 2016)

Regional and global temperature response to anthropogenic SO2 emissions from China in three climate models (Kasoar et al. 2016)

Effective radiative forcing from historical land use change (Andrews et al. 2016)

Reassessing properties and radiative forcing of contrail cirrus using a climate model (Bock & Burkhardt, 2016)

Could the Pliocene constrain the equilibrium climate sensitivity? (Hargreaves & Annan, 2016)

Influence of snow cover changes on surface radiation and heat balance based on the WRF model (Yu et al. 2016)

A sensitivity study of the impact of dynamic vegetation on simulated future climate change over Southern Europe and the Mediterranean (Alo & Anagnostou, 2016)

A satellite-based 13-year climatology of net cloud radiative forcing over the Indian monsoon region (Saud et al. 2016)

Separating climate change signals into thermodynamic, lapse-rate and circulation effects: theory and application to the European summer climate (Kröner et al. 2016)

Early global radiation measurements: a review (Stanhill & Archiman, 2016)

Aerosol types and radiative forcing estimates over East Asia (Bhawar et al. 2016)

Solar irradiance observed at Summit, Greenland: Possible links to magnetic activity on short timescales (Frederick, 2016)

Limits to global and Australian temperature change this century based on expert judgment of climate sensitivity (Grose et al. 2016)

Indirect Forcing of Black carbon on Clouds over North East India (Panicker et al. 2016)

Contrasting radiation and soil heat fluxes in Arctic shrub and wet sedge tundra (Juszak et al. 2016)

Aerosol radiative effects under clear skies over Europe and their changes in the period of 2001–2012 (Bartók, 2016)

Review of Aerosol-Cloud Interactions: Mechanisms, Significance and Challenges (Fan et al. 2016)

Inference of Climate Sensitivity from Analysis of Earth’s Energy Budget (Forster, 2016)

Impact of absorbing aerosol deposition on snow albedo reduction over the southern Tibetan plateau based on satellite observations (Lee et al. 2016)

Spatiotemporal characteristics of ultraviolet radiation in recent 54 years from measurements and reconstructions over the Tibetan Plateau (Liu et al. 2016)

The whole-atmosphere response to changes in the Earth’s magnetic field from 1900 to 2000: an example of “top-down” vertical coupling (Cnossen et al. 2016)

Strong modification of stratospheric ozone forcing by cloud and sea-ice adjustments (Xia et al. 2016)

Evaluation of the Arctic surface radiation budget in CMIP5 models (Boeke & Taylor, 2016)

Climate Feedback Variance and the Interaction of Aerosol Forcing and Feedbacks (Gettelman et al. 2016)

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New research – temperature (July 26, 2016)

Posted by Ari Jokimäki on July 26, 2016

Some of the latest papers on temperature are shown below. First a few highlighted papers with abstracts and then a list of some other papers. If this subject interests you, be sure to check also the other papers – they are by no means less interesting than the highlighted ones.


The rogue nature of hiatuses in a global warming climate (Sévellec, Sinha & Skliris, 2016)

Abstract: The nature of rogue events is their unlikelihood and the recent unpredicted decade-long slowdown in surface warming, the so-called hiatus, may be such an event. However, given decadal variability in climate, global surface temperatures were never expected to increase monotonically with increasing radiative forcing. Here, surface air temperature from twenty climate models is analysed to estimate the historical and future likelihood of hiatuses and “surges” (faster than expected warming), showing that the global hiatus of the early 21st Century was extremely unlikely. A novel analysis of future climate scenarios suggests that hiatuses will almost vanish and surges will strongly intensify by 2100 under a “business as usual” scenario. For “CO2 stabilisation” scenarios, hiatus and surge characteristics revert to typical 1940s values. These results suggest to study the hiatus of the early 21st Century and future re-occurrences as rogue events, at the limit of the variability of current climate modelling capability.

Underestimated warming of northern Canada in the Berkeley Earth temperature product (Way, Oliva & Viau, 2016)

Abstract: The Berkeley Earth surface temperature (BERK) project provides gridded global temperature anomaly products using an automated geostatistical approach to adjust station data for systematic biases. Despite its widespread usage, the BERK data set has not been evaluated at the national-scale, especially in data-sparse high latitude environments. This study provides an evaluation of the BERK product across all of Canada using 333 climate stations made available from the homogenized Environment Canada station network (HTcan). Comparison between co-located monthly air temperature anomalies for the two data sets suggests small differences between the two products for mean surface (∼2 m) air temperature. However, the relatively minimal bias in mean temperature is a consequence of contrasting cold and warm biases in minimum and maximum air temperatures, respectively, that are larger but effectively even out when averaged together. The BERK product is shown to exhibit systematic underestimation of recent regional warming in northern Canada which when combined with an overestimation of warmth earlier in the record results in an observable reduction in warming rates for minimum and mean temperature anomalies since 1950. The temporal evolution and spatial pattern of the observed biases suggest that the BERK-automated adjustments to station data in northern Canada miss some inhomogeneities in the raw station data. These results highlight the need for enhanced data recovery and homogenization efforts in data-sparse high latitude regions and emphasize the importance of national-scale climate data sets for evaluating global gridded products. We also recommend caution when using the BERK minimum and maximum monthly air temperature products for long-term trend analyses.

Revisiting whether recent surface temperature trends agree with the CMIP5 ensemble (Lin & Huybers, 2016)

Abstract: A weaker trend in global mean temperature over the past 15 years relative to the preceding decades has been characterized as significantly lower than those contained within the CMIP5 ensemble. In this study, divergence between model simulations and observations is estimated using a fixed-intercept linear trend with a slope estimator that has one-third the noise variance compared to simple linear regression. Following the approach of Fyfe et al. (2013) where inter-model spread is used to assess the distribution of trends, but using the fixed-intercept trend metric, demonstrates that recently observed trends in global-mean temperature are consistent (p > 0.1) with the CMIP5 ensemble for all 15-year intervals of observation-model divergence since 1970. Significant clustering of global trends according to modeling center indicates that the spread in CMIP5 trends is better characterized using ensemble members drawn across models, as opposed to using ensemble members from a single model. Despite model-observation consistency at the global level, substantial regional discrepancies in surface temperature trends remain.

Climate change in the Kola Peninsula, Arctic Russia, during the last 50 years from meteorological observations (Marshall, Vignols & Rees, 2016)

Abstract: We provide a detailed climatology and evaluation of recent climate change in the Kola Peninsula, Arctic Russia, a region influenced by both the North Atlantic and Arctic Oceans. The analysis is based on 50 years of monthly surface air temperature (SAT), precipitation (PPN) and sea level pressure (SLP) data from ten meteorological stations for 1966-2015. Regional mean annual SAT is ~0°C: the moderating effect of the ocean is such that coastal (inland) stations have a positive (negative) value. Examined mean annual PPN totals rise from ~430 mm in the north-east of the region to ~600 mm in the west.

Annual SAT in the Kola Peninsula has increased by 2.3 ± 1.0 °C over the past 50 years. Seasonally, statistically significant warming has taken place in spring and fall, although the largest trend has occurred in winter. While there has been no significant change in annual PPN, spring has become significantly wetter and fall drier. The former is associated with the only significant seasonal SLP trend (decrease). A positive winter North Atlantic Oscillation (NAO) index is generally associated with a warmer and wetter Kola Peninsula while a positive Siberian High (SH) index has the opposite impact. The relationship between both the NAO and SH and SAT is broadly coherent across the region whereas their relationship with PPN varies markedly, although none of the relationships are temporally invariant. Reduced sea ice in the Barents and White Seas and associated circulation changes are likely to be the principal drivers behind the observed changes.

Water temperature increases in the river Rhine in response to climate change (Hardenbicker et al. 2016)

Abstract: The present study analyzes climate change effects on the water temperature of the Rhine, one of the largest rivers in Central Europe. Simulation calculations were performed based on a range of climate and river flow projections for the near (2021–2050) and for the far future (2071–2100) compared to a reference period (1961–1990). Changes in mean annual water temperature in the near future range between +0.6 and +1.4 °C and between +1.9 and +2.2 °C in the far future (average of nine stations). Monthly mean values of the far future change in a more differentiated way by +0.4 to +1.3 °C in spring and +2.7 to +3.4 °C in late summer. The length of periods of high water temperature, expressed as successive days with water temperatures over 27 °C, increases by a factor of four until 2100. These prolonged durations of periods with unusually high water temperatures may provoke changes in the food web and in the rates of biological processes in the Rhine.

Other papers

Assessing the uncertainty of CESM-LE in simulating the trends of mean and extreme temperature and precipitation over China (Li, Zhu & Dong, 2016)

Reconciling Observed and Modelled Temperature and Precipitation Trends over Europe by Adjusting for Circulation Variability (Saffioti et al. 2016)

Geo-spatial analysis of temporal trends of temperature and its extremes over India using daily gridded (1°×1°) temperature data of 1969–2005 (Chakraborty et al. 2016)

Sudden stratospheric warmings observed in the last decade by satellite measurements (Kishore et al. 2016)

Longitudinal Asymmetric Trends of Tropical Cold-point Tropopause Temperature and Their Link to Strengthened Walker Circulation (Hu et al. 2016)

An in situ-based analysis of the relationship between land surface ‘skin’ and screen-level air temperatures (Good, 2016)

Spatiotemporal rainfall and temperature trends throughout the Brazilian Legal Amazon, 1973–2013 (Almeida et al. 2016)

Spatial variation of deterministic chaos in mean daily temperature and rainfall over Nigeria (Fuwape et al. 2016)

Homogenisation of temperature and precipitation time series with ACMANT3: method description and efficiency tests (Domonkos & Coll, 2016)

The tropical Pacific as a key pacemaker of the variable rates of global warming (Kosaka & Xie, 2016)

The changing shape of Northern Hemisphere summer temperature distributions (McKinnon et al. 2016)

Future Decreases in Freezing Days Across North America (Rawlins et al. 2016)

Arctic warming, moisture increase and circulation changes observed in the Ny-Ålesund homogenized radiosonde record (Maturilli & Kayser, 2016)

Trend analysis of air temperature time series in Greece and their relationship with circulation using surface and satellite data: recent trends and an update to 2013 (Feidas, 2016)

Urban Heat Island traverses in the City of Adelaide, South Australia (Clay et al. 2016)

Recent Extreme Arctic Temperatures are due to a Split Polar Vortex (Overland & Wang, 2016)

Potential tropical Atlantic impacts on Pacific decadal climate trends (Chikamoto et al. 2016)

Consistent land surface temperature data generation from irregularly spaced Landsat imagery (Fu & Weng, 2016)

Spatial and temporal variation in daily temperature indices in summer and winter seasons over India (1969–2012) (Kumar et al. 2016)

Spatial patterns of recent Antarctic surface temperature trends and the importance of natural variability: lessons from multiple reconstructions and the CMIP5 models (Smith & Polvani, 2016)

From Urban to National Heat Island: the effect of anthropogenic heat output on climate change in high population industrial countries (Murray & Heggie, 2016)

From accelerated warming to warming hiatus in China (Xie, Huang & Liu, 2016)

Weekly cycles in peak time temperatures and urban heat island intensity (Earl, Simmonds & Tapper, 2016)

Radiative and Dynamical Influences on Polar Stratospheric Temperature Trends (Ivy, Solomon & Rieder, 2016)

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Papers on early 20th century warming

Posted by Ari Jokimäki on August 29, 2013

This is a list of papers on early 20th century warming. List contains both observational and theoretical studies. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (April 15, 2015): Thompson et al. (2015) added.
UPDATE (April 8, 2014): Suo et al. (2013), Kelly et al. (1980), Petterssen (1949), Ahlmann (1948) added.

Early twentieth-century warming linked to tropical Pacific wind strength – Thompson et al. (2015)
“Of the rise in global atmospheric temperature over the past century, nearly 30% occurred between 1910 and 1940 when anthropogenic forcings were relatively weak. This early warming has been attributed to internal factors, such as natural climate variability in the Atlantic region, and external factors, such as solar variability and greenhouse gas emissions. However, the warming is too large to be explained by external factors alone and it precedes Atlantic warming by over a decade. For the late twentieth century, observations and climate model simulations suggest that Pacific trade winds can modulate global temperatures, but instrumental data are scarce in the early twentieth century. Here we present a westerly wind reconstruction (1894–1982) from seasonally resolved measurements of Mn/Ca ratios in a western Pacific coral that tracks interannual to multidecadal Pacific climate variability. We then reconstruct central Pacific temperatures using Sr/Ca ratios in a coral from Jarvis Island, and find that weak trade winds and warm temperatures coincide with rapid global warming from 1910 to 1940. In contrast, winds are stronger and temperatures cooler between 1940 and 1970, when global temperature rise slowed down. We suggest that variations in Pacific wind strength at decadal timescales significantly influence the rate of surface air temperature change.”
Diane M. Thompson, Julia E. Cole, Glen T. Shen, Alexander W. Tudhope & Gerald A. Meehl, Nature Geoscience 8, 117–121 (2015) doi:10.1038/ngeo2321.

External forcing of the early 20th century Arctic warming – Suo et al. (2013) “The observed Arctic warming during the early 20th century was comparable to present-day warming in terms of magnitude. The causes and mechanisms for the early 20th century Arctic warming are less clear and need to be better understood when considering projections of future climate change in the Arctic. The simulations using the Bergen Climate Model (BCM) can reproduce the surface air temperature (SAT) fluctuations in the Arctic during the 20th century reasonably well. The results presented here, based on the model simulations and observations, indicate that intensified solar radiation and a lull in volcanic activity during the 1920s–1950s can explain much of the early 20th century Arctic warming. The anthropogenic forcing could play a role in getting the timing of the peak warming correct. According to the model the local solar irradiation changes play a crucial role in driving the Arctic early 20th century warming. The SAT co-varied closely with local solar irradiation changes when natural external forcings are included in the model either alone or in combination with anthropogenic external forcings. The increased Barents Sea warm inflow and the anomalous atmosphere circulation patterns in the northern Europe and north Atlantic can also contribute to the warming. In summary, the early 20th century warming was largely externally forced.” Lingling Suo, Odd Helge Otterå, Mats Bentsen, Yongqi Gao, Ola M. Johannessen, Tellus A 2013, 65, 20578, [Full text]

Early 20th century warming in the Arctic: A review – Yamanouchi (2011) “From the 1920s to the 1940s, the Artic experienced significant warming that is comparable to the recent 30-year warming. The former warming was concentrated mostly in high latitudes, in contrast to the recent 30-year warming, which has occurred in all latitudes. Several explanations have been proposed; however, one of these proposed explanations, single external forcing, which could once explain the global average, failed to explain the early 20th century scenario. A second possible explanation was internal atmospheric variability with low frequency. Another candidate for the explanation was still forcing by black carbon deposited on snow and ice surfaces. The answer is most likely to be a combination of intrinsic internal natural climate variability and positive feedbacks that amplified the radiative and atmospheric forcing. We must continue our study by discovering historical data, analyzing ice cores, reanalyzing the Arctic system together with long-term reanalysis dating back to the 1880s, and also determine the contributions of each factor.” Takashi Yamanouchi, Polar Science, Volume 5, Issue 1, April 2011, Pages 53–71,

Early 20th century Arctic warming in retrospect – Wood & Overland (2010) “The major early 20th century climatic fluctuation (∼1920–1940) has been the subject of scientific enquiry from the time it was detected in the 1920s. The papers of scientists who studied the event first-hand have faded into obscurity but their insights are relevant today. We review this event through a rediscovery of early research and new assessments of the instrumental record. Much of the inter-annual to decadal scale variability in surface air temperature (SAT) anomaly patterns and related ecosystem effects in the Arctic and elsewhere can be attributed to the superposition of leading modes of variability in the atmospheric circulation. Meridional circulation patterns were an important factor in the high latitudes of the North Atlantic during the early climatic fluctuation. Sea surface temperature (SST) anomalies that appeared during this period were congruent with low-frequency variability in the climate system but were themselves most likely the result of anomalous forcing by the atmosphere. The high-resolution data necessary to verify this hypothesis are lacking, but the consistency of multiple lines of evidence provides strong support. Our findings indicate that early climatic fluctuation is best interpreted as a large but random climate excursion imposed on top of the steadily rising global mean temperature associated with anthropogenic forcing.” Kevin R. Wood, James E. Overland, International Journal of Climatology, Volume 30, Issue 9, pages 1269–1279, July 2010, DOI: 10.1002/joc.1973.

Influence of volcanic activity and changes in solar irradiance on surface air temperatures in the early twentieth century – Shiogama et al. (2006) “Causes of the global surface air temperature warming in the early half of the 20th century are examined using a climate model and an optimal detection/attribution methodology. While the anthropogenic response seems to be underestimated in our model, our previous study detected the influence due to natural external forcing, including the combined effects of solar irradiance changes and the recovery from large volcanic activity. We further partition the responses between these two natural external factors, detecting both the solar and the volcanic signal in the observed early warming. A diagnosis of the sensitivity to solar forcing and a volcanic super-eruption simulation suggest that our model possesses larger climate sensitivities to solar forcing and longer relaxation times to volcanic forcing than HadCM3, enabling us to detect both the solar and volcanic forcing responses.” Hideo Shiogama, Tatsuya Nagashima, Tokuta Yokohata, Simon A. Crooks, Toru Nozawa, Geophysical Research Letters, Volume 33, Issue 9, May 2006, DOI: 10.1029/2005GL025622.

Detecting natural influence on surface air temperature change in the early twentieth century – Nozawa et al. (2005) “We analyze surface air temperature datasets simulated by a coupled climate model forced with different external forcings, to diagnose the relative importance of these forcings to the observed warming in the early 20th century. The geographical distribution of linear temperature trends in the simulations forced only by natural contributions (volcanic eruptions and solar variability) shows better agreement with observed trends than that does the simulations forced only by well-mixed greenhouse gases. Using an optimal fingerprinting technique we robustly detect a significant natural contribution to the early 20th century warming. In addition, the amplitude of our simulated natural signal is consistent with the observations. Over the same period, however, we could not detect a greenhouse gas signal in the observed surface temperature in the presence of the external natural forcings. Hence our analysis suggests that external natural factors caused more warming in the early 20th century than anthropogenic factors.” Toru Nozawa, Tatsuya Nagashima, Hideo Shiogama, Simon A. Crooks, Geophysical Research Letters, Volume 32, Issue 20, October 2005, DOI: 10.1029/2005GL023540. [Full text]

The Early Twentieth-Century Warming in the Arctic—A Possible Mechanism – Bengtsson et al. (2004) “The huge warming of the Arctic that started in the early 1920s and lasted for almost two decades is one of the most spectacular climate events of the twentieth century. During the peak period 1930–40, the annually averaged temperature anomaly for the area 60°–90°N amounted to some 1.7°C. Whether this event is an example of an internal climate mode or is externally forced, such as by enhanced solar effects, is presently under debate. This study suggests that natural variability is a likely cause, with reduced sea ice cover being crucial for the warming. A robust sea ice–air temperature relationship was demonstrated by a set of four simulations with the atmospheric ECHAM model forced with observed SST and sea ice concentrations. An analysis of the spatial characteristics of the observed early twentieth-century surface air temperature anomaly revealed that it was associated with similar sea ice variations. Further investigation of the variability of Arctic surface temperature and sea ice cover was performed by analyzing data from a coupled ocean–atmosphere model. By analyzing climate anomalies in the model that are similar to those that occurred in the early twentieth century, it was found that the simulated temperature increase in the Arctic was related to enhanced wind-driven oceanic inflow into the Barents Sea with an associated sea ice retreat. The magnitude of the inflow is linked to the strength of westerlies into the Barents Sea. This study proposes a mechanism sustaining the enhanced westerly winds by a cyclonic atmospheric circulation in the Barents Sea region created by a strong surface heat flux over the ice-free areas. Observational data suggest a similar series of events during the early twentieth-century Arctic warming, including increasing westerly winds between Spitsbergen and Norway, reduced sea ice, and enhanced cyclonic circulation over the Barents Sea. At the same time, the North Atlantic Oscillation was weakening.” Bengtsson, Lennart, Vladimir A. Semenov, Ola M. Johannessen, 2004: The Early Twentieth-Century Warming in the Arctic—A Possible Mechanism. J. Climate, 17, 4045–4057. doi:;2. [Full text]

Solar and Greenhouse Gas Forcing and Climate Response in the Twentieth Century – Meehl et al. (2003) “Ensemble experiments with a global coupled climate model are performed for the twentieth century with time-evolving solar, greenhouse gas, sulfate aerosol (direct effect), and ozone (tropospheric and stratospheric) forcing. Observed global warming in the twentieth century occurred in two periods, one in the early twentieth century from about the early 1900s to the 1940s, and one later in the century from, roughly, the late 1960s to the end of the century. The model’s response requires the combination of solar and anthropogenic forcing to approximate the early twentieth-century warming, while the radiative forcing from increasing greenhouse gases is dominant for the response in the late twentieth century, confirming previous studies. Of particular interest here is the model’s amplification of solar forcing when this acts in combination with anthropogenic forcing. This difference is traced to the fact that solar forcing is more spatially heterogeneous (i.e., acting most strongly in areas where sunlight reaches the surface) while greenhouse gas forcing is more spatially uniform. Consequently, solar forcing is subject to coupled regional feedbacks involving the combination of temperature gradients, circulation regimes, and clouds. The magnitude of these feedbacks depends on the climate’s base state. Over relatively cloud-free oceanic regions in the subtropics, the enhanced solar forcing produces greater evaporation. More moisture then converges into the precipitation convergence zones, intensifying the regional monsoon and Hadley and Walker circulations, causing cloud reductions over the subtropical ocean regions, and, hence, more solar input. An additional response to solar forcing in northern summer is an enhancement of the meridional temperature gradients due to greater solar forcing over land regions that contribute to stronger West African and South Asian monsoons. Since the greenhouse gases are more spatially uniform, such regional circulation feedbacks are not as strong. These regional responses are most evident when the solar forcing occurs in concert with increased greenhouse gas forcing. The net effect of enhanced solar forcing in the early twentieth century is to produce larger solar-induced increases of tropical precipitation when calculated as a residual than for early century solar-only forcing, even though the size of the imposed solar forcing is the same. As a consequence, overall precipitation increases in the early twentieth century in the Asian monsoon regions are greater than late century increases, qualitatively consistent with observed trends in all-India rainfall. Similar effects occur in West Africa, the tropical Pacific, and the Southern Ocean tropical convergence zones.” Meehl, Gerald A., Warren M. Washington, T. M. L. Wigley, Julie M. Arblaster, Aiguo Dai, 2003: Solar and Greenhouse Gas Forcing and Climate Response in the Twentieth Century. J. Climate, 16, 426–444. doi:;2. [Full text]

Estimation of natural and anthropogenic contributions to twentieth century temperature change – Tett et al. (2002) “Using a coupled atmosphere/ocean general circulation model, we have simulated the climatic response to natural and anthropogenic forcings from 1860 to 1997. The model, HadCM3, requires no flux adjustment and has an interactive sulphur cycle, a simple parameterization of the effect of aerosols on cloud albedo (first indirect effect), and a radiation scheme that allows explicit representation of well-mixed greenhouse gases. Simulations were carried out in which the model was forced with changes in natural forcings (solar irradiance and stratospheric aerosol due to explosive volcanic eruptions), well-mixed greenhouse gases alone, tropospheric anthropogenic forcings (tropospheric ozone, well-mixed greenhouse gases, and the direct and first indirect effects of sulphate aerosol), and anthropogenic forcings (tropospheric anthropogenic forcings and stratospheric ozone decline). Using an “optimal detection” methodology to examine temperature changes near the surface and throughout the free atmosphere, we find that we can detect the effects of changes in well-mixed greenhouse gases, other anthropogenic forcings (mainly the effects of sulphate aerosols on cloud albedo), and natural forcings. Thus these have all had a significant impact on temperature. We estimate the linear trend in global mean near-surface temperature from well-mixed greenhouse gases to be 0.9 ± 0.24 K/century, offset by cooling from other anthropogenic forcings of 0.4 ± 0.26 K/century, giving a total anthropogenic warming trend of 0.5 ± 0.15 K/century. Over the entire century, natural forcings give a linear trend close to zero. We found no evidence that simulated changes in near-surface temperature due to anthropogenic forcings were in error. However, the simulated tropospheric response, since the 1960s, is ∼50% too large. Our analysis suggests that the early twentieth century warming can best be explained by a combination of warming due to increases in greenhouse gases and natural forcing, some cooling due to other anthropogenic forcings, and a substantial, but not implausible, contribution from internal variability. In the second half of the century we find that the warming is largely caused by changes in greenhouse gases, with changes in sulphates and, perhaps, volcanic aerosol offsetting approximately one third of the warming. Warming in the troposphere, since the 1960s, is probably mainly due to anthropogenic forcings, with a negligible contribution from natural forcings.” Simon F. B. Tett, Gareth S. Jones, Peter A. Stott, David C. Hill, John F. B. Mitchell, Myles R. Allen, William J. Ingram, Tim C. Johns, Colin E. Johnson, Andy Jones, David L. Roberts, David M. H. Sexton, Margaret J. Woodage, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 107, Issue D16, pages ACL 10-1–ACL 10-24, 27 August 2002, DOI: 10.1029/2000JD000028. [Full text]

Simulation of Early 20th Century Global Warming – Delworth & Knutson (2000) “The observed global warming of the past century occurred primarily in two distinct 20-year periods, from 1925 to 1944 and from 1978 to the present. Although the latter warming is often attributed to a human-induced increase of greenhouse gases, causes of the earlier warming are less clear because this period precedes the time of strongest increases in human-induced greenhouse gas (radiative) forcing. Results from a set of six integrations of a coupled ocean-atmosphere climate model suggest that the warming of the early 20th century could have resulted from a combination of human-induced radiative forcing and an unusually large realization of internal multidecadal variability of the coupled ocean-atmosphere system. This conclusion is dependent on the model’s climate sensitivity, internal variability, and the specification of the time-varying human-induced radiative forcing.” Thomas L. Delworth, Thomas R. Knutson, Science 24 March 2000: Vol. 287 no. 5461 pp. 2246-2250, DOI: 10.1126/science.287.5461.2246.

Changes in atmospheric circulation over northern hemisphere oceans associated with the rapid warming of the 1920s – Fu et al. (1999)
Global mean surface temperature has increased since the late 19th century. The warming occurred largely during two periods: 1920–1940, and since the mid-1970s. Although most recent studies have focused on the latter period, it is of interest to analyse the earlier period and compare its major features to the recent warming episode. The warming during 1920–1940 occurred most rapidly during the 1920s. It was strongest at high northern latitudes in winter, a pattern now believed to be characteristic of ‘greenhouse warming’. This warming of the Arctic was much discussed during the 1930s and 1940s, but the data available at that time were mostly derived from land areas. In this paper, we use the COADS marine data set and recent compilations of land surface temperature data sets to examine the behaviour of the surface fields over the ocean during this event. Considering the thermal and atmospheric fields at the surface, the strongest signal occurs in the North Atlantic Ocean during winter, being distinct but more gradual in the other oceans and seasons. The Northern Hemisphere continental record shows that both middle and high latitudes experienced rapid warming in the early 20th century warming interval (the 1920s and 1930s, hereafter referred to as ETCW). Temperature data for northern tropics, while displaying similar general characteristics, exhibit some differences with regard to timing and rates of change. There is a suggestion of weakening of the westerlies and the trade wind system in the 1930s, following an intensification of the westerlies across the North Atlantic during the previous two decades. This weakening may be related to a lessening of atmospheric baroclinicity in association with the fact that the amplitude of warming at high latitudes was much greater than that in low latitudes, reducing the mean meridional thermal gradient, and therefore the geostrophic pressure gradient. There is some indication that the North Atlantic and North Pacific high-pressure systems shifted northward. Coincident with this northward shift of the subtropical highs, typhoons in the Northwest Pacific and hurricanes in the North Atlantic became more numerous in this period of rising temperature, which we suggest is linked to a northward shift of the respective near-equatorial convergence zones. Concomitant to the weakening of the westerlies and trade wind systems, the Asian monsoon troughs deepened substantially, a situation generally favourable to the development of active monsoons. It is thought that the combination of these two features—enhanced continental monsoons and implied lowered vertical wind shear over the oceans—would tend to enhance the release of latent heat in the tropics, representing strengthened Hadley and Walker circulations, which may have been at least partly responsible for greater aridity in subtropical land areas of both hemispheres during this period. The latter is also consistent with an expansion and/or strengthening of the subtropical high-pressure belt into the continents.” Congbin Fu, Henry F. Diaz, Dongfeng Dong, Joseph O. Fletcher, International Journal of Climatology, Volume 19, Issue 6, pages 581–606, May 1999, DOI: 10.1002/(SICI)1097-0088(199905)19:63.0.CO;2-P.

Solar Forcing of Global Climate Change Since The Mid-17th Century – Reid et al. (1997) “Spacecraft measurements of the sun’s total irradiance since 1980 have revealed a long-term variation that is roughly in phase with the 11-year solar cycle. Its origin is uncertain, but may be related to the overall level of solar magnetic activity as well as to the concurrent activity on the visible disk. A low-pass Gaussian filtered time series of the annual sunspot number has been developed as a suitable proxy for solar magnetic activity that contains a long-term component related to the average level of activity as well as a short-term component related to the current phase of the 11-year cycle. This time series is also assumed to be a proxy for solar total irradiance, and the irradiance is reconstructed for the period since 1617 based on the estimate from climatic evidence that global temperatures during the Maunder Minimum of solar activity, which coincided with one of the coldest periods of the Little Ice Age, were about 1 °C colder than modern temperatures. This irradiance variation is used as the variable radiative forcing function in a one-dimensional ocean–climate model, leading to a reconstruction of global temperatures over the same period, and to a suggestion that solar forcing and anthropogenic greenhouse-gas forcing made roughly equal contributions to the rise in global temperature that took place between 1900 and 1955. The importance of solar variability as a factor in climate change over the last few decades may have been underestimated in recent studies.” George C. Reid, Climatic Change, October 1997, Volume 37, Issue 2, pp 391-405, DOI: 10.1023/A:1005307009726.

Changes in Global Surface Temperature From 1880 to 1977 Derived From Historical Records of Sea Surface Temperature – Paltridge & Woodruff (1981) “A preliminary analysis based primarily on historical records of sea surface temperature (SST) gives estimates of the change since 1880 of global, hemispheric and zonal average surface temperatures. The global change with time is roughly similar in shape and magnitude to that derived by Mitchell from land station data alone, but lags the Mitchell curve by 10-20 years. That is, the present data show a minimumof temperature somewhere between 1900 and 1925 and a maximum somewhere between 1945 and 1970. Comparing the means of these 25-year periods, the rise from minimum to maximum was (roughly) 0.6 K for the Northern Hemisphere and 0.9 K for the Southern Hemisphere. Comparing the means of the 50 years before 1930 and the 48 years from 1930 to 1977, the rise was 0.3 K for the Northern Hemisphere and 0.6 K for the Southern Hemisphere. The figures do not take into account the polar regions which, on linear extrapolation from lower latitudes, may have risen in temperature by twice the hemispheric averages. The temperature of the tropical zone (l0°N-10°S) has not changed over the years, so that the meridionaltemperature gradient has decreased in both hemispheres. The detail of the various conclusions may be revised later in the light of further analysis of the errors associated with the SST data sets. This furtheranalysis is underway at the Environmental Research Laboratories of NOAA.” Paltridge, G., S. Woodruff, 1981: Changes in Global Surface Temperature From 1880 to 1977 Derived From Historical Records of Sea Surface Temperature. Mon. Wea. Rev., 109, 2427–2434. doi:;2. [Full text]

Variations in Surface Air Temperatures: Part 2. Arctic Regions, 1881–1980 – Kelly et al. (1980) “We describe annual and seasonal changes in air temperatures over high latitudes of the Northern Hemisphere during the period 1881–1980. Trends (that is, fluctuations on time scales greater than 20 years) in the average temperature of the Arctic are compared with those of the Northern Hemisphere. Seasonal and regional departures from the long-term trends in the average temperature of the Arctic are identified. Spatial patterns of variation in the Arctic temperature field are determined by principal component analysis and the major characteristics of the time series of the dominant patterns are summarized. Trends in Arctic temperatures have been broadly similar to those for the Northern Hemisphere during the study period. The Arctic variations were, however, greater in magnitude and more rapid. The spatial pattern of change associated with the trend in Arctic temperatures is clearly identified by principal component analysis. It shows that the trends have, in general, been Arctic-wide, but that certain regions are particularly sensitive to long-term variations, most notably northwest Greenland and around the Kara Sea. There is some evidence that the pattern of Arctic cooling that occurred after 1940 was more complex than the warming that affected the whole Arctic during the 1920’s and 1930’s. Warming of the Arctic has occurred during the 1970’s, but is not yet of sufficient duration to be considered long term, except, perhaps, in spring. The average temperature of the Arctic during the 1970’s was equal to that of the 1960’s, indicating a cessation of the long-term cooling trend but not, as yet, a shift to long-term warming. Short-term variations in temperature appear to be most pronounced close to major regions of sea-ice production and decay.” Kelly, P. M., P. D. Jones, C. B. Sear, B. S. G. Cherry, R. K. Tavakol, 1982: Variations in Surface Air Temperatures: Part 2. Arctic Regions, 1881–1980. Mon. Wea. Rev., 110, 71–83. doi:;2. [Full text]

Temperature fluctuations and trends over the earth – Callendar (1961) “The annual temperature deviations at over 400 meteorological stations are combined on a regional basis to give the integrated fluctuations over large areas and zones. These are shown in graphical form, and it is concluded that a solar or atmospheric dust hypothesis is necessary to explain the world-wide fluctuations of a few years duration. An important change in the relationships of the zonal fluctuations has occurred since 1920. The overall temperature trends found from the data are considered in relation to the homogeneity of recording, and also to the evidence of glacial recession in different zones. It is concluded that the rising trend, shown by the instruments during recent decades, is significant from the Arctic to about 45°S lat., but quite small in most regions below 35°N. and not yet apparent in some. It is thought that the regional and zonal distribution of recent climatic trends is incompatible with the hypothesis of increased solar heating as the cause. On the other hand, the major features of this distribution are not incompatible with the hypothesis of increased carbon dioxide radiation, if the rate of atmospheric mixing between the hemispheres is a matter of decades rather than years.” G. S. Callendar, Quarterly Journal of the Royal Meteorological Society, Volume 87, Issue 371, pages 1–12, January 1961, DOI: 10.1002/qj.49708737102.

Changes in the General Circulation Associated with the Recent Climatic Variation – Petterssen (1949) No abstract. S. Petterssen, Geografiska Annaler, Vol. 31, Glaciers and Climate: Geophysical and Geomorphological Essays (1949), pp. 212-221.

The Present Climatic Fluctuation – Ahlmann (1948) No abstract. Hans W:Son Ahlmann, The Geographical Journal, Vol. 112, No. 4/6 (Oct. – Dec., 1948), pp. 165-193.

The artificial production of carbon dioxide and its influence on temperature – Callendar (1938) “By fuel combustion man has added about 150,000 million tons of carbon dioxide to the air during the past half century. The author estimates from the best available data that approximately three quarters of this has remained in the atmosphere. The radiation absorption coefficients of carbon dioxide and water vapour are used to show the effect of carbon dioxide on “sky radiation.” From this the increase in mean temperature, due to the artificial production of carbon dioxide, is estimated to be at the rate of 0.003°C. per year at the present time. The temperature observations at 200 meteorological stations are used to show that world temperatures have actually increased at an average rate of 0.005°C. per year during the past half century.” G. S. Callendar, Quarterly Journal of the Royal Meteorological Society, Volume 64, Issue 275, pages 223–240, April 1938, DOI: 10.1002/qj.49706427503. [Full text]

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Papers on tropopause height

Posted by Ari Jokimäki on May 7, 2013

This is a list of papers on tropopause height. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (May 12, 2013): Lakkis et al. (2009) added.

The determination of extratropical tropopause height in an idealized gray-radiation model – Zurita-Gotor & Vallis (2013) “This paper investigates the mechanisms that determine the extratropical tropopause height, extending previous results with a Newtonian cooling model. A primitive equation model forced by a meridional gradient of incoming solar radiation, with the outgoing infra-red radiation calculated using a simple gray radiation scheme, is now used. The tropopause is defined as the top of the boundary layer over which dynamical heat transport moves the temperature away from radiative equilibrium, and its height estimated from the isentropic mass flux. Depending on parameters, this tropopause may or may not be associated with a sharp stratification change, and it may or may not be possible to define a thermal tropopause. The mass flux and thermal tropopause display similar sensitivity to external parameters when the latter can be defined, a sensitivity in good agreement with predictions by a radiative constraint. In some contrast to the Newtonian model, the radiative constraint is now quite effective in preventing adjustment to marginal criticality with realistic parameters. The meridional structure of the thermal tropopause displays a jump in height at the jet latitude, which appears to be due to the formation of a mixing barrier at the jet maximum when baroclinicity has a finite vertical scale. As meridional potential vorticity mixing is inhibited across the jet, a discontinuity is created between weakly stratified air on its warm side and strongly stratified air on its cool side. The meridional stratification contrast is created by adiabatic cooling and warming by the residual circulation, as this circulation must be deflected vertically to avoid the mixing barrier at the jet maximum.” Pablo Zurita-Gotor, Geoffrey K. Vallis, Journal of the Atmospheric Sciences 2013, doi:

A numerical simulation of aerosols’ direct effects on tropopause height – Wu et al. (2013) “The direct effects of sulfate aerosol, dust aerosol, carbonaceous aerosol, and total combined aerosols on the tropopause height are simulated with the Community Atmospheric Model version 3.1 (CAM3.1). A decrease of global mean tropopause height induced by sulfate, carbonaceous aerosol, and total combined aerosols is found, and a tropopause height increase is induced by dust aerosol. Sulfate aerosol decreases the tropospheric temperature and increases the stratospheric temperature. These effects cause a decrease in the height of the tropopause. In contrast, carbonaceous and total combined aerosols increase both the tropospheric and the stratospheric temperatures, and they also cause a decrease in the height of the tropopause. The changes in the tropopause height show highly statistically significant correlations with the changes in the tropospheric and stratospheric temperatures. The changes in the tropospheric and stratospheric temperatures are related to the changes in the radiative heat rate, cloud cover, and latent heat, but none of these factors absolutely dominate the temperature change.” Jian Wu, Yanyan Xu, Qian Yang, Zhiwei Han, Deming Zhao, Jianping Tang, Theoretical and Applied Climatology, May 2013, Volume 112, Issue 3-4, pp 659-671, DOI: 10.1007/s00704-012-0760-5.

A global blended tropopause based on ERA data. Part II: Trends and tropical broadening – Wilcox et al. (2012) “A new tropopause definition involving a flow-dependent blending of the traditional thermal tropopause with one based on potential vorticity has been developed and applied to the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalyses (ERA), ERA-40 and ERA-Interim. Global and regional trends in tropopause characteristics for annual and solsticial seasonal means are presented here, with emphasis on significant results for the newer ERA-Interim data for 1989–2007. The global-mean tropopause is rising at a rate of 47 m per decade, with pressure falling at 1.0 hPa per decade and temperature falling at 0.18 K per decade. The Antarctic tropopause shows decreasing heights, warming and increasing westerly winds. The Arctic tropopause also shows a warming, but with decreasing westerly winds. In the Tropics the trends are small, but at the latitudes of the subtropical jets they are almost double the global values. It is found that these changes are mainly concentrated in the eastern hemisphere. Previous and new metrics for the rate of broadening of the Tropics, based on both height and wind, give trends in the range 0.9–2.2° per decade. For ERA-40 the global height and pressure trends for the period 1979–2001 are similar: 39 m per decade and −0.8 hPa per decade. These values are smaller than those found from the thermal tropopause definition with this dataset, as was used in most previous studies.” L. J. Wilcox, B. J. Hoskins, K. P. Shine, Quarterly Journal of the Royal Meteorological Society, Volume 138, Issue 664, pages 576–584, April 2012 Part A, DOI: 10.1002/qj.910. [Full text]

A global blended tropopause based on ERA data. Part I: Climatology – Wilcox et al. (2012) “A new tropopause definition, based on a flow-dependent blending of the traditional thermal tropopause with one based on potential vorticity, has been developed. The benefits of such a blending algorithm are most apparent in regions with synoptic-scale fluctuations between tropical and extratropical air masses. The properties of the local air mass determine the relative contributions to the location of the blended tropopause, rather than this being determined by a specified function of latitude. Global climatologies of tropopause height, temperature, potential temperature and zonal wind, based on European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA) ERA-Interim data, are presented for the period 1989–2007. Features of the seasonal-mean tropopause are discussed on a global scale, alongside a focus on selected monthly climatologies for the two high-latitude regions and the tropical belt. The height differences between climatologies based on ERA-Interim and ERA-40 data are also presented. Key spatial and temporal features seen in earlier climatologies, based mainly on the World Meteorological Organization thermal tropopause definition, are reproduced with the new definition. Tropopause temperatures are consistent with those from earlier climatologies, despite some differences in height in the extratropics.” L. J. Wilcox, B. J. Hoskins, K. P. Shine, Quarterly Journal of the Royal Meteorological Society, Volume 138, Issue 664, pages 561–575, April 2012 Part A, DOI: 10.1002/qj.951.

Monitoring Cirrus Cloud and Tropopause Height over Hanoi Using a Compact Lidar System – Hai et al. (2012) “Cirrus clouds in the upper troposphere and the lower stratosphere have attracted great attention due to their important role and impact on the atmospheric radioactive balance. Because cirrus clouds are located high in the atmosphere, their study requires a high resolution remote sensing technique not only for detection but also for the characterization of their properties. The lidar technique with its inherent high sensitivity and resolution has become an indispensible tool for studying and improving our understanding of cirrus cloud. Using lidar technique we can simultaneously measure the cloud height, thickness and follow its temporal evolution. In this paper we describe the development of a compact and highly sensitive lidar system with the aim to remotely monitor for the first time the cirrus clouds over Hanoi (21001’42’’N, 105051’12’’W). From the lidar data collected during the year 2011. We derive the mean cloud height, location of cloud top, the cloud mean thickness and their temporal evolution. We then compare the location of the cloud top with the position of the tropopause determined the radiosonde data and found good that the distance between cloud top and tropopause remains fairly stable, indicating that generally the top of cirrus clouds is the good tracer of the tropopause. We found that the cirrus clouds are generally located at height between 11.2 to 15 km with average height of 13.4 km. Their thickness is between 0.3 and 3.8 km with average value of 1.7 km. We also compare the properties of cirrus cloud with that observed at other locations around the world based on lidar technique.” Bui Van Hai, Dinh Van Trung, Nguyen Xuan Tuan, Dao Duy Thang, Nguyen Thanh Binh, Communications in Physics, Vol 22, No 4 (2012).

Dynamics of Midlatitude Tropopause Height in an Idealized Model – Zurita-Gotor & Vallis (2011) “This paper investigates the factors that determine the equilibrium state, and in particular the height and structure of the tropopause, in an idealized primitive equation model forced by Newtonian cooling in which the eddies can determine their own depth. Previous work has suggested that the midlatitude tropopause height may be understood as the intersection between a radiative and a dynamical constraint. The dynamical constraint relates to the lateral transfer of energy, which in midlatitudes is largely effected by baroclinic eddies, and its representation in terms of mean-flow properties. Various theories have been proposed and investigated for the representation of the eddy transport in terms of the mean flow, including a number of diffusive closures and the notion that the flow evolves to a state marginally supercritical to baroclinic instability. The radiative constraint expresses conservation of energy and so must be satisfied, although it need not necessarily be useful in providing a tight constraint on tropopause height. This paper explores whether and how the marginal criticality and radiative constraints work together to produce an equilibrated flow and a tropopause that is internal to the fluid. The paper investigates whether these two constraints are consistent with simulated variations in the tropopause height and in the mean state when the external parameters of an idealized primitive equation model are changed. It is found that when the vertical redistribution of heat is important, the radiative constraint tightly constrains the tropopause height and prevents an adjustment to marginal criticality. In contrast, when the stratification adjustment is small, the radiative constraint is only loosely satisfied and there is a tendency for the flow to adjust to marginal criticality. In those cases an alternative dynamical constraint would be needed in order to close the problem and determine the eddy transport and tropopause height in terms of forcing and mean flow.” Zurita-Gotor, Pablo, Geoffrey K. Vallis, 2011: Dynamics of Midlatitude Tropopause Height in an Idealized Model. J. Atmos. Sci., 68, 823–838. doi: [Full text]

Recent widening of the tropical belt from global tropopause statistics: Sensitivities – Birner et al. (2010) “Several recent studies have shown evidence for a widening of the tropical belt over the past few decades. One line of evidence uses statistics of the tropopause height to distinguish between tropics and extratropics and defines tropical edge latitudes as those latitudes at which the number of days per year with tropopause heights greater than 15 km exceeds a certain threshold (typically 200 days/yr). This definition involves two somewhat arbitrary thresholds. Here the sensitivity of the resulting widening trend of the tropical belt to these thresholds is investigated using four different reanalysis data sets. Widening trends are found to be particularly sensitive to changes in the tropopause height threshold. Ways to objectively determine appropriate thresholds to define tropical edge latitudes based on tropopause statistics are presented. Trend estimates for the width of the tropical belt from different reanalysis data sets are found to be mostly inconsistent with each other despite consistent seasonal and interannual variations.” Thomas Birner, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 115, Issue D23, 16 December 2010, DOI: 10.1029/2010JD014664. [Full text]

The Impact of Stratospheric Ozone Recovery on Tropopause Height Trends – Son et al. (2009) “The evolution of the tropopause in the past, present, and future climate is examined by analyzing a set of long-term integrations with stratosphere-resolving chemistry climate models (CCMs). These CCMs have high vertical resolution near the tropopause, a model top located in the mesosphere or above, and, most important, fully interactive stratospheric chemistry. Using such CCM integrations, it is found that the tropopause pressure (height) will continue to decrease (increase) in the future, but with a trend weaker than that in the recent past. The reduction in the future tropopause trend is shown to be directly associated with stratospheric ozone recovery. A significant ozone recovery occurs in the Southern Hemisphere lower stratosphere of the CCMs, and this leads to a relative warming there that reduces the tropopause trend in the twenty-first century. The future tropopause trends predicted by the CCMs are considerably smaller than those predicted by the Intergovernmental Panel on Climate Change Fourth Assessment Report (AR4) models, especially in the southern high latitudes. This difference persists even when the CCMs are compared with the subset of the AR4 model integrations for which stratospheric ozone recovery was prescribed. These results suggest that a realistic representation of the stratospheric processes might be important for a reliable estimate of tropopause trends. The implications of these finding for the Southern Hemisphere climate change are also discussed.” Son, Seok-Woo, and Coauthors, 2009: The Impact of Stratospheric Ozone Recovery on Tropopause Height Trends. J. Climate, 22, 429–445. doi: [Full text]

Monitoring cirrus clouds with lidar in the Southern Hemisphere: A local study over Buenos Aires. 1. Tropopause heights – Lakkis et al. (2009) “Cirrus clouds in the upper troposphere and the lower stratosphere have recently drawn much attention due to their important role and impact on the atmospheric radiative balance. Because they are located in the upper troposphere their study requires a high resolution technique not only to detect them but also to characterize their behaviour and evolution. A good dynamic range in lidar backscattering signals is necessary to observe and improve our knowledge of cirrus clouds, and thereof, atmospheric parameters in the troposphere and UT/LS due to their vicinity to the tropopause layer. The lidar system measures, in real time, the evolution of the atmospheric boundary layer, stratospheric aerosols, tropopause height and cirrus clouds evolution. The aim of the work is to present the main properties of cirrus clouds over central Argentina and to monitor tropopause height together with their temporal evolution using a backscatter lidar system located in Buenos Aires (34.6 °S, 58.5 °W). A cirrus clouds detection method was used to analyze a set of 60 diurnal events, during 2001–2005, in order to estimate tropopause height and its temporal evolution, using the top of cirrus clouds present on the upper troposphere as a tropopause tracer. The results derived from lidar show a remarkable good agreement when compared with rawinsonde data, considering values of tropopause height with differences less than or equal to 500 m, depending on the signal to noise ratio of the measurements. Clouds properties analysis reveals the presence of thick cirrus clouds with thickness between 0.5 and 4.2 km, with the top cloud located at the tropopause height.” Susan Gabriela Lakkis, Mario Lavorato, Pablo Osvaldo Canziani, Atmospheric Research, Volume 92, Issue 1, March 2009, Pages 18–26, [Full text]

Tropopause height and zonal wind response to global warming in the IPCC scenario integrations – Lorenz & DeWeaver (2007) “The change in the extratropical circulation under global warming is studied using the climate models participating in the Intergovernmental Panel on Climate Change (IPCC) fourth assessment report. The IPCC models predict a strengthening and a poleward shift of the tropospheric zonal jets in response to global warming. The change in zonal jets is also accompanied by a strengthening and a poleward and upward shift of transient kinetic energy and momentum flux. Similar changes in circulation are simulated by a simple dry general circulation model (GCM) when the height of the tropopause is raised. The similarity between the simple GCM and the IPCC models suggests that the changes in midlatitude circulation are predominantly driven by a rise in the height of the tropopause, and that other factors such as increased moisture content and the change in the low-level pole-to-equator temperature gradient, play a secondary role. In addition, the variability about the ensemble-mean of the zonal wind response is significantly correlated with the variability of the tropopause height response over the polar cap, especially in the Southern Hemisphere.” David J. Lorenz, Eric T. DeWeaver, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 112, Issue D10, 27 May 2007, DOI: 10.1029/2006JD008087. [Full text]

Contributions of Anthropogenic and Natural Forcing to Recent Tropopause Height Changes – Santer et al. (2003) “Observations indicate that the height of the tropopause—the boundary between the stratosphere and troposphere—has increased by several hundred meters since 1979. Comparable increases are evident in climate model experiments. The latter show that human-induced changes in ozone and well-mixed greenhouse gases account for ∼80% of the simulated rise in tropopause height over 1979–1999. Their primary contributions are through cooling of the stratosphere (caused by ozone) and warming of the troposphere (caused by well-mixed greenhouse gases). A model-predicted fingerprint of tropopause height changes is statistically detectable in two different observational (“reanalysis”) data sets. This positive detection result allows us to attribute overall tropopause height changes to a combination of anthropogenic and natural external forcings, with the anthropogenic component predominating.” B. D. Santer, M. F. Wehner, T. M. L. Wigley, R. Sausen, G. A. Meehl, K. E. Taylor, C. Ammann, J. Arblaster, W. M. Washington, J. S. Boyle, W. Brüggemann, Science 25 July 2003: Vol. 301 no. 5632 pp. 479-483, DOI: 10.1126/science.1084123. [Full text]

Use of changes in tropopause height to detect human influences on climate – Sausen & Santer (2003) “The height of the global-mean tropopause shows a steady increase since 1979 in re-analyses of numerical weather forecasts. This is in agreement with results from a climate model driven by natural and anthropogenic forcings. Superimposed on the multi-decadal overall trends in both simulations and re-analyses are higher-frequency fluctuations (with periods of few years) related to explosive volcanic eruptions. Global-mean tropopause height has the desirable property of acting as a natural filter, removing much of the ENSO variability that hampers the interpretation of tropospheric and surface temperature changes. In model simulations with anthropogenic forcings, changes in tropopause height can be detected roughly 20 years earlier than changes in surface temperature.” Sausen, Robert; Santer, Benjamin D., Meteorologische Zeitschrift, Volume 12, Number 3, 1 June 2003 , pp. 131-136(6), DOI:

Determining the tropopause height from gridded data – Reichler et al. (2003) “A method is presented to determine tropopause height from gridded temperature data with coarse vertical resolution. The algorithm uses a thermal definition of the tropopause, which is based on the concept of a “threshold lapse-rate”. Interpolation is performed to identify the pressure at which this threshold is reached and maintained for a prescribed vertical distance. The method is verified by comparing the heights calculated from analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) with the observed heights at individual radiosonde stations. RMS errors in the calculated tropopause heights are generally small. They range from 30–40 hPa in the extratropics to 10–20 hPa in the tropics. The largest deviations occur in the subtropics, where the tropopause has strong meridional gradients that are not adequately resolved by the input data.” Thomas Reichler, Martin Dameris, Robert Sausen, Geophysical Research Letters, Volume 30, Issue 20, October 2003, DOI: 10.1029/2003GL018240. [Full text]

Behavior of tropopause height and atmospheric temperature in models, reanalyses, and observations: Decadal changes – Santer et al. (2003) “We examine changes in tropopause height, a variable that has hitherto been neglected in climate change detection and attribution studies. The pressure of the lapse rate tropopause, pLRT, is diagnosed from reanalyses and from integrations performed with coupled and uncoupled climate models. In the National Centers for Environmental Prediction (NCEP) reanalysis, global-mean pLRT decreases by 2.16 hPa/decade over 1979–2000, indicating an increase in the height of the tropopause. The shorter European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis has a global-mean pLRT trend of −1.13 hPa/decade over 1979–1993. Simulated pLRT trends over the past several decades are consistent with reanalysis results. Superimposed on the overall increase in tropopause height in models and reanalyses are pronounced height decreases following the eruptions of El Chichón and Pinatubo. Interpreting these pLRT results requires knowledge of both T(z), the initial atmospheric temperature profile, and ΔT(z), the change in this profile in response to external forcing. T(z) has a strong latitudinal dependence, as does ΔT(z) for forcing by well-mixed greenhouse gases and stratospheric ozone depletion. These dependencies help explain why overall tropopause height increases in reanalyses and observations are amplified toward the poles. The pronounced increases in tropopause height in the climate change integrations considered here indicate that even AGCMs with coarse vertical resolution can resolve relatively small externally forced changes in tropopause height. The simulated decadal-scale changes in pLRT are primarily thermally driven and are an integrated measure of the anthropogenically forced warming of the troposphere and cooling of the stratosphere. Our algorithm for estimating pLRT (based on a thermal definition of tropopause height) is sufficiently sensitive to resolve these large-scale changes in atmospheric thermal structure. Our results indicate that the simulated increase in tropopause height over 1979–1997 is a robust, zero-order response of the climate system to forcing by well-mixed greenhouse gases and stratospheric ozone depletion. At the global-mean level, we find agreement between the simulated decadal-scale pLRT changes and those estimated from reanalyses. While the agreement between simulated pLRT changes and those in NCEP is partly fortuitous (due to excessive stratospheric cooling in NCEP), it is also driven by real pattern similarities. Our work illustrates that changes in tropopause height may be a useful “fingerprint” of human effects on climate and are deserving of further attention.” B. D. Santer, R. Sausen, T. M. L. Wigley, J. S. Boyle, K. AchutaRao, C. Doutriaux, J. E. Hansen, G. A. Meehl, E. Roeckner, R. Ruedy, G. Schmidt, K. E. Taylor, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 108, Issue D1, pages ACL 1-1–ACL 1-22, 16 January 2003, DOI: 10.1029/2002JD002258.

Interannual variability of the tropical tropopause derived from radiosonde data and NCEP reanalyses – Randel et al. (2003) “Interannual variability of the tropical tropopause is studied using long time series of radiosonde data, together with global tropopause analyses from the National Centers for Environmental Prediction (NCEP) reanalyses over 1957–1997. Comparisons for the period 1979–1997 show the NCEP tropopause temperature is too warm by ∼3–5 K and too high in pressure by ∼2–6 mbar. However, these biases are approximately constant in time, so that seasonal and interannual variability is reasonably well captured by the NCEP data. Systematic differences in NCEP tropopause statistics are observed between the presatellite (1957–1978) and postsatellite (1979–1997) periods, precluding the use of the reanalyses for the study of multidecadal variability. Interannual anomalies in tropical average radiosonde and NCEP data show variations of order ±1–2 K over the period 1979–1997, but there can be differences between these two estimates which are of similar magnitude. These differences impact estimates of decadal trends: During 1979–1997, negative trends in tropopause temperature of order −0.5 K/decade are observed in radiosonde data but are not found in NCEP reanalyses. The space-time patterns of several coherent signals are identified in both sets of tropopause statistics. The volcanic eruption of El Chichón (1982) warmed the tropical tropopause by ∼1–2 K and lowered its altitude by ∼200 m for approximately 1–2 years. Smaller tropopause variations are observed following Mount Pinatubo (1991), particularly in radiosonde data. The signatures of the quasi-biennial oscillation (QBO) and El-Nino/Southern Oscillation (ENSO) events are strong in tropopause statistics. QBO variations are primarily zonal mean in character, while ENSO events exhibit dipole patterns over Indonesia and the central Pacific Ocean, with small signals for zonal averages.” William J. Randel, Fei Wu, Dian J. Gaffen, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 105, Issue D12, pages 15509–15523, 27 June 2000, DOI: 10.1029/2000JD900155. [Full text]

Climatological characteristics of the tropical tropopause as revealed by radiosondes – Seidel et al. (2001) “A temporally and spatially comprehensive depiction of the tropical tropopause is presented, based on radiosonde data from 83 stations. Climatological statistics for 1961–1990 are computed for three levels: the conventional lapse-rate tropopause (LRT), the cold-point tropopause (CPT), and the 100 hPa level. Mean values and seasonal and interannual variations of temperature, pressure, height, potential temperature, and water vapor saturation mixing ratio at these levels are compared. The tropopause is higher, colder, and at lower pressure in the Northern Hemisphere (NH) than in the Southern Hemisphere (SH) in NH winter. This pattern reverses in NH summer, except that the tropopause remains colder in the NH than in the SH. The climatological locations of minimum tropopause temperature differ from those of maximum height and minimum pressure: In NH winter the tropopause is coldest over the western tropical Pacific warm pool region, but it is highest and at lowest pressure over the western Atlantic. Correlations of interannual anomalies in zonal-mean characteristics reveal that the height of the tropopause reflects the temperature of the underlying troposphere. Tropopause temperature, on the other hand, shows little association with tropospheric characteristics but is significantly correlated with the temperature and pressure of the lower stratosphere. The 100 hPa level is a poor surrogate for the tropical tropopause. Changes in radiosonde instrumentation limit the potential for detecting tropopause trends. However, the following (nonmonotonic) trends in the tropopause in the deep tropics during 1978–1997 seem robust: an increase in height of about 20 m decade−1, a decrease in pressure of about 0.5 hPa decade−1, a cooling of about 0.5 K decade−1, little change in potential temperature, and a decrease in saturation volume mixing ratio of about 0.3 ppmv decade−1.” Dian J. Seidel, Rebecca J. Ross, James K. Angell, George C. Reid, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 106, Issue D8, pages 7857–7878, 27 April 2001, DOI: 10.1029/2000JD900837. [Full text]

Stratospheric Influence on Tropopause Height: The Radiative Constraint – Thuburn & Craig (2000) “Earlier theoretical and modeling work introduced the concept of a radiative constraint relating tropopause height to tropospheric lapse rate and other factors such as surface temperature. Here a minimal quantitative model for the radiative constraint is presented and used to illustrate the essential physics underlying the radiative constraint, which involves the approximate balance between absorption and emission of thermal infrared (IR) radiation determining tropopause temperature. The results of the minimal model are then extended in two ways. First, the effects of including a more realistic treatment of IR radiation are quantified. Second, the radiative constraint model is extended to take into account non-IR warming processes such as solar heating and dynamical warming near the tropopause. The sensitivity of tropopause height to non-IR warming is estimated to be a few kilometers per K day−1, with positive warming leading to a lower tropopause. Sensitivities comparable to this are found in GCM experiments in which imposed changes in the ozone distribution or in the driving of the stratospheric residual mean meridional circulation lead to changes in tropopause height. In the Tropics the influence of the stratospheric circulation is found to extend down at least as far as the main convective outflow level, some 5 km below the temperature minimum.” Thuburn, John, George C. Craig, 2000: Stratospheric Influence on Tropopause Height: The Radiative Constraint. J. Atmos. Sci., 57, 17–28. doi:;2. [Full text]

Correlations between tropopause height and total ozone: Implications for long-term changes – Steinbrecht et al. (1998) “For the central European station of Hohenpeissenberg, averaging of ozone profiles grouped by tropopause height shows that the ozone mixing ratio profile in the lower stratosphere shifts up and down with the tropopause. The shift is largest near the tropopause and becomes negligible above 20 to 25 km. As a consequence a high tropopause is correlated with low total ozone and a low tropopause with high total ozone. Independent of season, total ozone decreases by 16 Dobson units (DU) per kilometer increase in tropopause height. At Hohenpeissenberg the tropopause has moved up by 150±70 m (2 σ) per decade over the last 30 years. If the −16 DU per kilometer correlation between total ozone and tropopause height is valid on the timescale of years, it is speculated that the observed increase in tropopause height could explain about 25% of the observed −10 DU per decade decrease of total ozone. This is of the same magnitude as the 30% fraction of midlatitude ozone depletion which current stratospheric models have difficulty accounting for. For Hohenpeissenberg the increase in tropopause height appears to be correlated with observed tropospheric warming: At 5 km altitude, for example, temperature has increased by 0.7±0.3 K per decade (2 σ) since 1967.” W. Steinbrecht, H. Claude, U. Köhler, K. P. Hoinka, Journal of Geophysical Research: Atmospheres (1984–2012), Volume 103, Issue D15, pages 19183–19192, 20 August 1998, DOI: 10.1029/98JD01929.

A comparison of ozone and thermal tropopause heights and the impact of tropopause definition on quantifying the ozone content of the troposphere – Bethan et al. (1996) “A comparison has been conducted of the height and sharpness of the tropopause as revealed by temperature and ozone profiles. In the study, 628 ECC-type ozonesonde profiles from four stations in northern Europe were used. Two tropopauses were defined for each profile: a thermal tropopause and an ozone tropopause defined in terms of both mixing ratio and vertical gradient of mixing ratio. On average, the ozone tropopause lay 800 m below the thermal. Large differences in tropopause height were associated with indefinite thermal tropopauses which were, in turn, often associated with cyclonic conditions (some corresponding to profiles taken within the stratospheric polar vortex). On almost all profiles the thermal tropopause was the higher of the two, and of the 15 profiles that did not fit this pattern, two-thirds were associated with anticyclonic flow in the upper troposphere. It is also shown that the tropopause definition impacts greatly on the evaluation of the ozone content of the troposphere. Where the thermal tropopause is indefinite in character, on average 27% of the ozone found below the thermal tropopause lies above the ozone tropopause.” S. Bethan, G. Vaughan, S. J. Reid, Quarterly Journal of the Royal Meteorological Society, Volume 122, Issue 532, pages 929–944, April 1996 Part B, DOI: 10.1002/qj.49712253207.

On the Height of the Tropopause and the Static Stability of the Troposphere – Held (1982) “Speculative arguments are, presented that describe how radiative and dynamical constraints conspire to determine the height of the tropopause and the tropospheric static stability in midlatitudes and in the tropics. The arguments suggest an explanation for the observation that climatological isentropic slopes in midlatitudes are close to the critical slope required for baroclinic instability in a two-layer model.” Held, Issac M., 1982: On the Height of the Tropopause and the Static Stability of the Troposphere. J. Atmos. Sci., 39, 412–417. doi:;2. [Full text]

Quasi-Biennial Variations in Temperature, Total Ozone, and Tropopause Height – Angell & Korshover (1964) “An analysis of mean-monthly temperature and total ozone data suggests that quasi-biennial oscillations extend to the temperate and polar latitudes of both hemispheres. Basically, there is symmetry with respect to the equator, although the oscillations show up most clearly in the Southern Hemisphere, and there is a tendency for the biennial maximum of temperature and total ozone to occur in the spring. Harmonic analysis implies a poleward drift of the biennial maximum of temperature and total ozone at a rate near 0.2 m sec−1, with the drift becoming indistinct poleward of 40°. The quasi-biennial variation in total ozone is very nearly in phase with the quasi-biennial variation in 50-mb temperature. There is also a quasi-biennial variation in tropopause height associated with the temperature oscillation in the lower stratosphere. There is weak evidence for a quasi-biennial variation in beryllium-7 in the lower stratosphere.” Angell, J. K., J. Korshover, 1964: Quasi-Biennial Variations in Temperature, Total Ozone, and Tropopause Height. J. Atmos. Sci., 21, 479–492. doi:;2. [Full text]

Some ozone-weather relationships in the middle latitudes of the Southern Hemisphere – Kulkarni (1963)
The paper discusses relationships observed between ozone and the upper-air measurements made at Brisbane, Aspendale and Macquarie Island. The correlation coefficients between the short-term fluctuations of ozone and the temperatures at 100, 200 and 300 mb levels at these places are presented. In general, high ozone was observed to be associated with the sinking of the tropopause, descending of stratospheric air, warming of the lower stratosphere and a southerly flow of air in the lower stratosphere. At Macquarie Island, an instance of the ozone fluctuations in the baroclinic waves of the polar night westerly vortex suggested that the middle stratospheric waves contributed to the unexplained long term variance in total ozone. The meteorological parameters at the 200 mb level did not reveal the type of oscillation shown by the spring maximum level of ozone with a periodicity of 24 months. From the study of the 60 mb temperatures, it is concluded that the middle stratospheric circulation is playing an important role in deciding the spring level of ozone in middle latitudes of the Southern Hemisphere.” R. N. Kulkarni, Quarterly Journal of the Royal Meteorological Society, Volume 89, Issue 382, pages 478–489, October 1963, DOI: 10.1002/qj.49708938205.

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Papers on snow cover changes

Posted by Ari Jokimäki on February 19, 2013

This is a list of papers on snow cover changes with an emphasis on hemispheric and global observational analyses. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (October 19, 2014): Armstrong & Brodzik (2001) added. Regional section with a few papers added.

Change in snow phenology and its potential feedback to temperature in the Northern Hemisphere over the last three decades – Peng et al. (2013) “Trends in the duration or extent of snow cover are expected to feedback to temperature trends. We analyzed trends in dates of onset and termination of snow cover in relation to temperature over the past 27 years (1980–2006) from over 636 meteorological stations in the Northern Hemisphere. Different trends in snow duration are observed over North America and Eurasia. Over North America, the termination date of snow cover remained stable during the 27 years, whereas over Eurasia it has advanced by 2.6 ± 5.6 d decade−1. Earlier snow cover termination is systematically correlated on a year-to-year basis with a positive temperature anomaly during the snowmelt month with a sensitivity of −0.077 °C d−1. These snow feedbacks to air temperature are more important in spring, because high net radiation is coupled with thin snow cover. Shushi Peng et al 2013 Environ. Res. Lett. 8 014008 doi:10.1088/1748-9326/8/1/014008. [Full text]

Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty – Brown & Robinson (2011) “An update is provided of Northern Hemisphere (NH) spring (March, April) snow cover extent (SCE) over the 1922–2010 period incorporating the new climate data record (CDR) version of the NOAA weekly SCE dataset, with annual 95% confidence intervals estimated from regression analysis and intercomparison of multiple datasets. The uncertainty analysis indicates a 95% confidence interval in NH spring SCE of ±5–10% over the pre-satellite period and ±3–5% over the satellite era. The multi-dataset analysis shows larger uncertainties monitoring spring SCE over Eurasia (EUR) than North America (NA) due to the more complex regional character of the snow cover variability and larger between-dataset variability over northern Europe and north-central Russia. Trend analysis of the updated SCE series provides evidence that NH spring snow cover extent has undergone significant reductions over the past ~90 yr and that the rate of decrease has accelerated over the past 40 yr. The rate of decrease in March and April NH SCE over the 1970–2010 period is ~0.8 million km2 per decade corresponding to a 7% and 11% decrease in NH March and April SCE respectively from pre-1970 values. In March, most of the change is being driven by Eurasia (NA trends are not significant) but both continents exhibit significant SCE reductions in April. The observed trends in SCE are being mainly driven by warmer air temperatures, with NH mid-latitude air temperatures explaining ~50% of the variance in NH spring snow cover over the 89-yr period analyzed. However, there is also evidence that changes in atmospheric circulation around 1980 involving the North Atlantic Oscillation and Scandinavian pattern have contributed to reductions in March SCE over Eurasia. Brown, R. D. and Robinson, D. A.: Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty, The Cryosphere, 5, 219-229, doi:10.5194/tc-5-219-2011, 2011. [Full text]

Long-term variability in Northern Hemisphere snow cover and associations with warmer winters – McCabe & Wolock (2010) “A monthly snow accumulation and melt model is used with gridded monthly temperature and precipitation data for the Northern Hemisphere to generate time series of March snow-covered area (SCA) for the period 1905 through 2002. The time series of estimated SCA for March is verified by comparison with previously published time series of SCA for the Northern Hemisphere. The time series of estimated Northern Hemisphere March SCA shows a substantial decrease since about 1970, and this decrease corresponds to an increase in mean winter Northern Hemisphere temperature. The increase in winter temperature has caused a decrease in the fraction of precipitation that occurs as snow and an increase in snowmelt for some parts of the Northern Hemisphere, particularly the mid-latitudes, thus reducing snow packs and March SCA. In addition, the increase in winter temperature and the decreases in SCA appear to be associated with a contraction of the circumpolar vortex and a poleward movement of storm tracks, resulting in decreased precipitation (and snow) in the low- to mid-latitudes and an increase in precipitation (and snow) in high latitudes. If Northern Hemisphere winter temperatures continue to warm as they have since the 1970s, then March SCA will likely continue to decrease. Gregory J. McCabe, David M. Wolock, Climatic Change, March 2010, Volume 99, Issue 1-2, pp 141-153, DOI: 10.1007/s10584-009-9675-2.

Changing Northern Hemisphere Snow Seasons – Choi et al. (2010) “Spatial and temporal patterns in the onset, offset, and length of the snow season across Northern Hemisphere continents are examined for the period from 1967 to 2008. Full snow seasons (FSS) and core snow seasons (CSS) are defined based on the consistency of snow cover within a location over the course of the cold season. Climatologically, the seasonal onsets of FSS and CSS progress more rapidly across the continents than the slower spring northward offset. Average Northern Hemisphere FSS duration has decreased at a rate of 0.8 week decade−1 (5.3 days decade−1) between the winters of 1972/73 and 2007/08, while there is no significant hemispheric change in CSS duration. Changes in the FSS duration are attributed primarily to a progressively earlier offset, which has advanced poleward at a rate of 5.5 days decade−1. A major change in the trends of FSS offset and duration occurred in the late 1980s. Earlier FSS offsets, ranging from 5 to 25 days, and resultant abbreviated durations are observed in western Europe, central and East Asia, and the mountainous western United States. Where regional changes in CSS were observed, most commonly there were shifts in both onset and offset dates toward earlier dates. Results indicate that it is important to pay close attention to spring snowmelt as an indicator of hemispheric climate variability and change. Choi, Gwangyong, David A. Robinson, Sinkyu Kang, 2010: Changing Northern Hemisphere Snow Seasons. J. Climate, 23, 5305–5310. doi: [Full text]

Recent Northern Hemisphere snow cover extent trends and implications for the snow-albedo feedback – Déry & Brown (2007) “Monotonic trend analysis of Northern Hemisphere snow cover extent (SCE) over the period 1972–2006 with the Mann-Kendall test reveals significant declines in SCE during spring over North America and Eurasia, with lesser declines during winter and some increases in fall SCE. The weekly mean trend attains −1.28, −0.78, and −0.48 × 106 km2 (35 years)−1 over the Northern Hemisphere, North America, and Eurasia, respectively. The standardized SCE time series vary and trend coherently over Eurasia and North America, with evidence of a poleward amplification of decreasing SCE trends during spring. Multiple linear regression analyses reveal a significant dependence of the retreat of the spring continental SCE on latitude and elevation. The poleward amplification is consistent with an enhanced snow-albedo feedback over northern latitudes that acts to reinforce an initial anomaly in the cryospheric system. Stephen J. Déry, Ross D. Brown, Geophysical Research Letters, Volume 34, Issue 22, November 2007, DOI: 10.1029/2007GL031474. [Full text]

Variability and trends in the annual snow-cover cycle in Northern Hemisphere land areas, 1972–2000 – Dye (2002) “This study investigated variability and trends in the annual snow-cover cycle in regions covering high-latitude and high-elevation land areas in the Northern Hemisphere. The annual snow-cover cycle was examined with respect to the week of the last-observed snow cover in spring (WLS), the week of the first-observed snow cover in autumn (WFS), and the duration of the snow-free period (DSF). The analysis used a 29-year time-series (1972–2000) of weekly, visible-band satellite observations of Northern Hemisphere snow cover from NOAA with corrections applied by D. Robinson of Rutgers University Climate Laboratory. Substantial interannual variability was observed in WLS, WFS and DSF (standard deviations of 0·8–1·1, 0·7–0·9 and 1·0–1·4 weeks, respectively), which is related directly to interannual variability in snow-cover area in the regions and time periods of snow-cover transition. Over the nearly three-decade study period, WLS shifted earlier by 3–5 days/decade as determined by linear regression analysis. The observed shifts in the annual snow-cover cycle underlie a significant trend toward a longer annual snow-free period. The DSF increased by 5–6 days/decade over the study period, primarily as a result of earlier snow cover disappearance in spring. The observed trends are consistent with reported trends in the timing and length of the active growing season as determined from satellite observations of vegetation greenness and the atmospheric CO2 record. Dennis G. Dye, Hydrological Processes, Volume 16, Issue 15, pages 3065–3077, 30 October 2002, DOI: 10.1002/hyp.1089.

Recent northern hemisphere snow extent: A comparison of data derived from visible and microwave satellite sensors – Armstrong & Brodzik (2001)
Abstract: “During the past four decades much important information on Northern Hemisphere snow extent has been provided by the NOAA weekly snow extent charts derived from visible-band satellite imagery. Passive microwave satellite remote sensing can enhance snow measurements based on visible data alone because of the ability to penetrate clouds, provide data during darkness and the potential to provide an index of snow depth or water equivalent. We compare the fluctuation of Northern Hemisphere snow cover over the past twenty years using these two satellite remote sensing techniques. Results show comparable inter-annual variability with similar long-term hemispheric-scale trends indicating decreases in snow extent of approximately 0.2 percent per year. The passive microwave snow algorithm applied in this study indicates less snow-covered area than the visible data during fall and early winter when the snow is shallow. New algorithms designed to reduce this apparent error are being developed and tested.”
R. L. Armstrong, M. J. Brodzik (2001), Recent northern hemisphere snow extent: A comparison of data derived from visible and microwave satellite sensors. Geophysical Research Letters, 28: 3673–3676. doi: 10.1029/2000GL012556. [FULL TEXT]

Northern Hemisphere Snow Cover Variability and Change, 1915–97 – Brown (2000) “Historical and reconstructed snow cover data from stations in Canada, the United States, the former Soviet Union, and the People’s Republic of China were used to reconstruct monthly snow cover extent (SCE) fluctuations over midlatitudinal (40°–60°N) regions of North America (NA) and Eurasia back to the early 1900s using an areal snow index approach. The station distribution over NA allowed SCE to be reconstructed back to 1915 for 6 months (November–April), along with estimates of monthly mean snow water equivalent (SWE) from gridded daily snow depth data. Over Eurasia, SCE was able to be reconstructed back to 1922, but major gaps in the station network limited the approach to 3 months (October, March, and April). The reconstruction provided evidence of a general twentieth century increase in NA SCE, with significant increases in winter (December–February) SWE averaging 3.9% per decade. The results are consistent with an observed increasing trend in winter snow depth over Russia and provide further evidence for systematic increases in precipitation over NH midlatitudes. North American spring snow cover was characterized by rapid decreases during the 1980s and early 1990s with a significant long-term decrease in April SWE averaging 4.4% per decade. Eurasia was characterized by a significant reduction in April SCE over the 1922–97 period associated with a significant spring warming. The snow cover reduction was significant at the hemispheric scale with an estimated average NH SCE loss of 3.1 × 106 km2 (100 yr)−1 associated with significant warming of 1.26°C (100 yr)−1 over NH midlatitudinal land areas (40°–60°N). The computed temperature sensitivity of NH April SCE was −2.04 × 106 km2 °C−1. Since 1950, March SCE decreases have become more important than those in April with significant reductions over both continents averaging 8.5 × 106 km2 (100 yr)−1. March was also observed to have experienced the largest warming during the November–April snow season with significant post-1950 warming trends in both continents averaging 4.1°C (100 yr)−1. The hemisphere-wide elevated March snow cover–temperature response is consistent with the position of the snowline over continental grassland vegetation zones where snow cover is relatively shallow and the potential snow cover area–albedo feedback is large.” Brown, Ross D., 2000: Northern Hemisphere Snow Cover Variability and Change, 1915–97. J. Climate, 13, 2339–2355. doi:;2. [Full text]

Northern Hemisphere snow extent: regional variability 1972–1994 – Frei & Robinson (1999) “Snow cover is an important hydrologic and climatic variable due to its effects on water supplies, and on energy and mass exchanges at the surface. We investigate the kinematics and climatology of Northern Hemisphere snow extent between 1972 and 1994, and associated circulation patterns. Interannual fluctuations of North American and Eurasian snow extents are driven by both hemispheric scale signals, as well as signals from smaller ‘coherent’ regions, within which interannual fluctuations of snow extent are highly correlated. These regions cover only 2–6% of the continental land area north of 20°N, yet during many months they explain more than 60% of the variance in continental snow extent. They are identified using Principal Components Analysis (PCA) of digitized snow extent charts obtained from the National Oceanic and Atmospheric Administration (NOAA). Significant month-to-month persistence is found over western North America and Europe during winter and spring. Geographically and seasonally dependent associations are identified between North American snow extent and atmospheric circulation patterns, surface air temperature, and snowfall. Over western North America, snow extent is associated with the longitudinal position of the North American ridge. Over eastern North America, snow extent is associated with a meridional oscillation in the 500-mb geopotential height field. These teleconnection patterns, derived using composite analyses, are associated with secondary modes of tropospheric variability during autumn and winter. During spring, snow extent becomes effectively decoupled from tropospheric dynamics. These results are useful for understanding the natural variability of the climate system, reconstructing pre-satellite era climate variability, evaluating climate models, and detecting climate change. Allan Frei, David A. Robinson, International Journal of Climatology, Volume 19, Issue 14, pages 1535–1560, 30 November 1999, DOI: 10.1002/(SICI)1097-0088(19991130)19:143.0.CO;2-J. [Full text]

Recent variations and regional relationships in Northern Hemisphere snow cover – Robinson et al. (1995) Abstract doesn’t seem to be available online. Robinson, David A.; Frei, Allan; Serreze, Mark C., Annals of Glaciology, vol.21, pp.71-76.

Changes of Snow Cover, Temperature, and Radiative Heat Balance over the Northern Hemisphere – Groisman et al. (1994) “Contemporary large-scale changes in satellite-derived snow cover were examined over the Northern Hemisphere extratropical land (NEL) areas. These areas encompass 55% of the land in the Northern Hemisphere. Snow cover (S) transient regions, the “centers of action” relative to interannual variations of snow cover, were identified for the years 1972–1992. During these years a global retreat in snow cover extent (SE) occurred in the second half of the hydrologic year (April–September). Mean annual SE has decreased by 10% (2.3 × 106 km2). Negative trends account for one-third to one-half of the interannual continental variance of SE. The historical influence of S on the planetary albedo and outgoing longwave radiation (OLR) is investigated. The mean annual response of the S feedback on the radiative balance (RB) is negative and suggests a large-scale heat redistribution. During autumn and early winter (up to January), however, the feedback of S on the planetary RB may he positive. Only by February does the cooling effect of S (due to albedo increase) dominate the planetary warming due to reduced OLR over the S. Despite a wintertime maximum in SF, the feedback in spring has the greatest magnitude. The global retreat of spring SE should lead to a positive feedback on temperature. Based on observed records of S, changes in RB are calculated that parallel an observed increase of spring temperature during the past 20 years. The results provide a partial explanation of the significant increase in spring surface air temperature observed over the land areas of the Northern Hemisphere during the past century. The mean SE in years with an El Niño and La Niña were also evaluated. El Niño events are generally accompanied by increased SE over the NEL during the first half of the hydrological year. In the second half of the hydrologic year (spring and summer), the El Niño events are accompanied by a global retreat of SE. Groisman, Pavel Ya, Thomas R. Karl, Richard W. Knight, Georgiy L. Stenchikov, 1994: Changes of Snow Cover, Temperature, and Radiative Heat Balance over the Northern Hemisphere. J. Climate, 7, 1633–1656. doi:;2. [Full text]

Global Snow Cover Monitoring: An Update – Robinson et al. (1993) “Accurate monitoring of the large-scale dimensions of global snow cover is essential for understanding details of climate dynamics and climate change. Presently, such information is gathered individually from ground station networks and satellite platforms. Efforts are in progress to consolidate and analyze long-term station records from a number of countries. To gain truly global coverage, however, satellite-based monitoring techniques must be employed. A 27-year record of Northern Hemisphere continental snow cover produced by the National Oceanic and Atmospheric Administration (NOAA) is the longest such environmental record available. Records of Southern Hemisphere continental cover and snow on top of Arctic sea ice have been produced by similar means for a portion of this interval. The visible imagery charting technique used to generate these data provides information on snow extent but not on snow volume. Satellite microwave analyses over Northern Hemisphere lands show some promise in this regard, however, large-scale monitoring of snow extent with microwave data remains less accurate than visible charting. This paper updates the status of global snow cover monitoring, concentrating on the weekly snow charts prepared by NOAA and discussing a new and consistent record of monthly snow cover generated from these weekly charts. The NOAA charts show a reduction of hemispheric snow cover over the past five years, particularly in spring. Snow areas from the NOAA product are then compared with values derived using passive microwave data. The latter consistently reports less snow cover than the more accurate visible product. Finally, future snow monitoring initiatives are recommended. These include continuing the consistent NOAA product until an all-weather all-surface product is developed. The latter would use multiple data sources and geographic information systems techniques. Such an integrative product would need extensive comparisons with the NOAA product to ensure the continued utility of the lengthy NOAA observations in studies of climate change. In a retrospective sense, satellite charts from the middle 1960s to early 1970s need reevaluation and techniques to merge satellite products with historic station time series must be developed. Robinson, David A., Kenneth F. Dewey, Richard R. Heim, 1993: Global Snow Cover Monitoring: An Update. Bull. Amer. Meteor. Soc., 74, 1689–1696. doi:;2. [Full text]

Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere – Gutzler & Rosen (1992) “Digitized maps of Northern Hemisphere snow cover derived from visible satellite imagery are examined to assess the interannual variability of snow cover in winter months for years 1972–90. The secular trend of winter snow cover over the landmasses of Eurasia and North America during this period is extremely small in December and January. A decreasing trend of somewhat larger magnitude is observed in Eurasian snow cover in February. Fluctuations of detrended interannual snow-cover anomalies averaged over the Eurasian and North American continents are positively correlated. By subdividing the continents into longitudinal sectors it is determined that this intercontinental relationship is due to high correlations between European and North American sectors. The relationship of snow-cover fluctuations to large-scale circulation anomalies is described using lime series of teleconnection pattern indices derived from monthly mean geopotential height fields. A pattern of height anomalies resembling the North Atlantic Oscillation is correlated with snow-cover anomalies in North America and Europe. The Pacific-North American teleconnection pattern is highly correlated with snow-cover anomalies in western North America but has limited influence on intercontinental snow-cover fluctuations.” Gutzler, David S., Richard D. Rosen, 1992: Interannual Variability of Wintertime Snow Cover across the Northern Hemisphere. J. Climate, 5, 1441–1447. doi:;2. [Full text]

Recent secular variations in the extent of Northern Hemisphere snow cover – Robinson & Dewey (1990) “Northern hemisphere snow cover during 1988 and 1989 was at its lowest extent since the advent of reliable satellite snow-cover monitoring in 1972; running some 8–10% below the eighteen-year annual mean of 25.7 million km2. Monthly minima for the period of record occurred six times during these two years. In general, the last nine years of the satellite record had less extensive cover than the 1972–80 interval. Negative anomalies during the 1980s were largest over Eurasia in all seasons, and in the Spring over North America. Hemispheric seasonal means for the most recent nine years were 3.7% to 8.4% lower than those between 1972 and 1980. Results are based on analyses of National Oceanic and Atmospheric Administration weekly snow charts, which are produced from visible satellite imagery.” David A. Robinson, Kenneth F. Dewey, Geophysical Research Letters, Volume 17, Issue 10, pages 1557–1560, September 1990, DOI: 10.1029/GL017i010p01557. [Full text]

A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980 – Dewey & Heim (1982) “The purpose of this article is to acquaint the research community with a new data base—a digitized archive of Northern Hemisphere snow cover. Historically, those researchers who needed snow cover data for climatic and atmospheric boundary layer studies have had to rely on the irregularly spaced (and in some regions, sparse)grid of point observations. Northern Hemisphere Weekly Snow and Ice Cover Charts, which are created from analyzed satellite imagery at the National Earth Satellite Service (NESS), have been available on an operational basis since late 1966. Each of these weekly charts for the period November 1966 through December 1980 was digitized and stored in a new data archive. Snow cover area and snow cover frequency climatologies were created and examples are presented. The significance of this unique data archive is examined by comparing the 14-year mean annual snow cover frequency climatology with several published snow cover climatologies. The potential uses for this data archive in meteorological and climatological studies also are reviewed. Dewey, Kenneth F., Richard Heim, 1982: A Digital Archive of Northern Hemisphere Snow Cover, November 1966 through December 1980. Bull. Amer. Meteor. Soc., 63, 1132–1141. doi:;2. [Full text]

Regional analyses





North America

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Papers on the Anthropocene

Posted by Ari Jokimäki on January 15, 2013

This is a list of papers on the new geological epoch called the Anthropocene. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

The Anthropocene: is there a geomorphological case? – Brown et al. (2013) “The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’ effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes, geomorphology has to be an integral part of this consideration given that it is Earth surface processes that produce terrestrial and near-shore stratigraphy. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The working Group is now considering the practical and aspects of such a formalisation including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’.” Antony G. Brown, Stephen Tooth, Richard C. Chiverrell, Jim Rose, David S. G. Thomas, John Wainwright, Joanna E. Bullard, Varyl Thorndycraft, Rolf Aalto, Peter Downs, Earth Surface Processes and Landforms, DOI: 10.1002/esp.3368.

Agro-industrial alluvium in the Swale catchment, northern England, as an event marker for the Anthropocene – Foulds et al. (2013) “Physically and chemically distinctive late-Prehistoric and historical age alluvial deposits are characteristic of many upland and lowland river systems in the UK. Despite their widespread distribution, there have been few attempts to construct robust chronologies or to identify environmental factors that governed their formation. The Swale catchment in northern England is typical in this respect, with large areas of its valley floor covered by sedimentologically distinctive laminated sands and silts, enriched in organic material and Pb, and underlain by uncontaminated and structureless silts. Using 14C dating, chemostratigraphy, lichenometry and historical maps, a catchment-wide change in sedimentation style has been dated to between the mid 18th and early 19th centuries AD. Several causative factors were responsible for this change in sedimentation style and include the initiation of large-scale, intensive lead mining from the latter half of the 18th century onwards, embankment construction in the lowlands and historical peat erosion in the uplands. Transformation of the Swale floodplain also reflects longer-term land-use and climate change. In particular, deforestation of headwater tributaries by monastic grazing practices in the High Middle Ages (AD 1000–1300) led to a period of fine-grained sedimentation in upland catchments, as well as priming hillslopes for erosion and widespread channel network incision and increased fine sediment flux during the climatic downturn of the ‘Little Ice Age’. Sediment facies of a similar nature have been widely recorded in other northern English river catchments and represent a regional land use–climate signal characteristic of the Anthropocene. We introduce the term ‘agro-industrial alluvium’ to describe these types of deposit. They have similarities to post-settlement alluvium in North America and Australia, where historical land-use change had a similar impact on valley floor sedimentology.” Simon A Foulds, Mark G Macklin, Paul A Brewer, The Holocene January 8, 2013 0959683612465445, doi: 10.1177/0959683612465445.

Holocene and Anthropocene Landscape Change: Arroyo Formation on Santa Cruz Island, California – Perroy et al. (2012) “In this study, we untangle the relative importance of climatic, tectonic, and anthropogenic drivers as triggers of arroyo formation and geomorphic change for a small watershed on Santa Cruz Island, California. Within the Pozo watershed (6.47 km2), historic arroyo incision occurred contemporaneously with arroyo incision across many of the world’s dryland regions. Unlike many of these other sites, Pozo contains a datable record that allows quantification of sedimentation rates from the mid-to-late Holocene to the twentieth century. Basin-wide environmental changes were assessed using a combination of cosmogenic radionuclide inventories, midden and marine-shell deposits, relict soil properties, airborne and ground-based light detection and ranging (lidar) data, ranching artifacts, and historic records. Shortly after the introduction of sheep in 1853, localized sedimentation rates on the Pozo floodplain increased by two orders of magnitude from 0.4 mm/year to 25 mm/year. Accelerated sedimentation was followed by arroyo formation ca. 1878 and rapid expansion of the incipient gully network, the lateral extent of which has been largely maintained since 1929. Catchment-mean erosion rates from cosmogenic radionuclide measurements indicate that presettlement rates were less than 0.08 mm/year, whereas lidar-derived measurements of historic gully erosion produce estimates almost thirty times higher (2.2 mm/year). Topographic measurements since 2005 indicate that the active channel of the Pozo watershed is aggrading. We argue that accelerated sedimentation due to overgrazing, and an unusually large 1878 rainstorm event, set the stage for arroyo formation in the Pozo watershed between 1875 and 1886. We hypothesize that even in the absence of modern human disturbance, downcutting would have occurred due to intrinsic hillslope stability thresholds.” Ryan L. Perroy, Bodo Bookhagen, Oliver A. Chadwick & Jeffrey T. Howarth, Annals of the Association of American Geographers, Volume 102, Issue 6, 2012, DOI:10.1080/00045608.2012.715054.

Cause of the chalcophile trace element enrichments marking the Holocene to Anthropocene transition in northern Chesapeake Bay sediments – Dolor et al. (2012) “In Chesapeake Bay sediments, concentrations of 15 chalcophile trace elements, half rarely determined in estuaries, display historical profiles having remarkably similar features. All element concentrations rose more or less simultaneously in the 1920–1940 interval, creating a chemostratigraphic marker of the Holocene to Anthropocene transition. Subsequently, concentration maxima occurred at ∼20-year intervals, suggesting a link to a documented climate cycle of similar period. These elements’ correlated profiles suggest that sediments approximate binary mixtures of one lithogenic and one multi-element anthropogenic component. The latter component is characterized by these mass ratios (±standard error): [View Within Article]. Where comparisons are possible, these ratios differ from those of contaminants in the harbor of the region’s principal industrial city, Baltimore, but are surprisingly similar to those in sediment contaminants from the Susquehanna River, the Bay’s chief tributary. Thus both the anthropogenic and the lithogenic components in the Bay’s central channel appear to originate in the river basin. Many chalcophile element ratios in the anthropogenic component are similar to those in regional aerosols. If cumulative aerosol deposition on soils in the river basin is the source of the anthropogenic component, then the above ratios could be a regional anthropogenic signature that should be looked for more widely. Unlike Mo, the enrichment of these chalcophile elements in the Bay’s sediments is not controlled by seasonal anoxia; Mo apparently possesses a unique capacity to record past redox information about estuaries owing to its high seawater concentration.” Marvourneen K. Dolor, George R. Helz, William F. McDonough, Geochimica et Cosmochimica Acta, Volume 82, 1 April 2012, Pages 79–91,

Is the Anthropocene an issue of stratigraphy or pop culture? – Autin & Holbrook (2012) “The term Anthropocene recently entered into the rhetoric of both the scientific community and the popular environmental movement. Scientific proponents argue that global industrialization drives accelerated Earth-system changes unrivaled in Earth’s history. The discussion now filters into geological stratigraphy with proposals to amend formal time stratigraphic nomenclature (Zalasiewicz et al., 2008, 2010). Environmentalists suggest that terms like Anthropocene foster broad social and cultural awareness of human-induced environmental changes. Advocates argue that greater awareness of humanity’s role in environmental change encourages sustainable resource utilization. Formal recognition of a new geologic epoch helps the broader scientific community solidify the idea of humanity as an Earth-system driver. Before the scientific community ventures too far, we wish to offer comment that considers the practicality of the Anthropocene to geological stratigraphy, the science to which it ultimately applies.” Whitney J. Autin, John M. Holbrook, GSA Today, Volume 22 Issue 7 (July 2012). [Full text]

The Anthropocene: a new epoch of geological time? – Zalasiewicz et al. (2011) “Anthropogenic changes to the Earth’s climate, land, oceans and biosphere are now so great and so rapid that the concept of a new geological epoch defined by the action of humans, the Anthropocene, is widely and seriously debated. Questions of the scale, magnitude and significance of this environmental change, particularly in the context of the Earth’s geological history, provide the basis for this Theme Issue. The Anthropocene, on current evidence, seems to show global change consistent with the suggestion that an epoch-scale boundary has been crossed within the last two centuries.” Jan Zalasiewicz, Mark Williams, Alan Haywood and Michael Ellis, Phil. Trans. R. Soc. A 13 March 2011 vol. 369 no. 1938 835-841, doi: 10.1098/rsta.2010.0339. [Full text]

The New World of the Anthropocene – Zalasiewicz et al. (2010) “The Anthropocene, following the lost world of the Holocene, holds challenges for both science and society.” Jan Zalasiewicz, Mark Williams, Will Steffen, Paul Crutzen, Environ. Sci. Technol., 2010, 44 (7), pp 2228–2231, DOI: 10.1021/es903118j. [Full text]

Are we now living in the Anthropocene? – Zalasiewicz et al. (2008) “The term Anthropocene, proposed and increasingly employed to denote the current interval of anthropogenic global environmental change, may be discussed on stratigraphic grounds. A case can be made for its consideration as a formal epoch in that, since the start of the Industrial Revolution, Earth has endured changes sufficient to leave a global stratigraphic signature distinct from that of the Holocene or of previous Pleistocene interglacial phases, encompassing novel biotic, sedimentary, and geochemical change. These changes, although likely only in their initial phases, are sufficiently distinct and robustly established for suggestions of a Holocene–Anthropocene boundary in the recent historical past to be geologically reasonable. The boundary may be defined either via Global Stratigraphic Section and Point (“golden spike”) locations or by adopting a numerical date. Formal adoption of this term in the near future will largely depend on its utility, particularly to earth scientists working on late Holocene successions. This datum, from the perspective of the far future, will most probably approximate a distinctive stratigraphic boundary.” Jan Zalasiewicz, Mark Williams, Alan Smith, Tiffany L. Barry, Angela L. Coe, Paul R. Bown, Patrick Brenchley, David Cantrill, Andrew Gale, Philip Gibbard, F. John Gregory, Mark W. Hounslow, Andrew C. Kerr, Paul Pearson, Robert Knox, John Powell, Colin Waters, John Marshall, Michael Oates, Peter Rawson, and Philip Stone, GSA Today 18 (2): 4-8, 1 Feb 2008. [Full text]

The Anthropocene: Are Humans Now Overwhelming the Great Forces of Nature – Steffen et al. (2007) “We explore the development of the Anthropocene, the current epoch in which humans and our societies have become a global geophysical force. The Anthropocene began around 1800 with the onset of industrialization, the central feature of which was the enormous expansion in the use of fossil fuels. We use atmospheric carbon dioxide concentration as a single, simple indicator to track the progression of the Anthropocene. From a preindustrial value of 270–275 ppm, atmospheric carbon dioxide had risen to about 310 ppm by 1950. Since then the human enterprise has experienced a remarkable explosion, the Great Acceleration, with significant consequences for Earth System functioning. Atmospheric CO2 concentration has risen from 310 to 380 ppm since 1950, with about half of the total rise since the preindustrial era occurring in just the last 30 years. The Great Acceleration is reaching criticality. Whatever unfolds, the next few decades will surely be a tipping point in the evolution of the Anthropocene.” Will Steffen, Paul J. Crutzen, John R. McNeill, AMBIO: A Journal of the Human Environment 36(8):614-621. 2007, doi:;2.

Humans as geologic agents: A deep-time perspective – Wilkinson (2005) “Humans move increasingly large amounts of rock and sediment during various construction activities, and mean rates of cropland soil loss may exceed rates of formation by up to an order of magnitude, but appreciating the actual importance of humans as agents of global erosion necessitates knowledge of prehistoric denudation rates imposed on land surfaces solely by natural processes. Amounts of weathering debris that compose continental and oceanic sedimentary rocks provide one such source of information and indicate that mean denudation over the past half-billion years of Earth history has lowered continental surfaces by a few tens of meters per million years. In comparison, construction and agricultural activities currently result in the transport of enough sediment and rock to lower all ice-free continental surfaces by a few hundred meters per million years. Humans are now an order of magnitude more important at moving sediment than the sum of all other natural processes operating on the surface of the planet. Relationships between temporal trends in land use and global population indicate that humans became the prime agents of erosion sometime during the latter part of the first millennium A.D.” Bruce H. Wilkinson, Geology, v. 33 no. 3 p. 161-164, doi: 10.1130/G21108.1. [Full text]

Fluvial filtering of land-to-ocean fluxes: from natural Holocene variations to Anthropocene – Meybeck & Vörösmarty (2005) “The evolution of river systems and their related fluxes is considered at various time scales: (i) over the last 18 000 years, under climatic variability control, (ii) over the last 50 to 200 years (Anthropocene) due to direct human impacts. Natural Holocene variations in time and space depend on (i) land-to-ocean connections (endorheism, glacial cover, exposure of continental shelf); (ii) types of natural fluvial filters (e.g., wetlands, lakes, floodplains, estuaries). Anthropocene changes concern (i) land–ocean connection (e.g., partial to total runoff reduction resulting from water management), (ii) modification and removal of natural filters, (iii) creation of new filters, particularly irrigated fields and reservoirs, (iv) acceleration and/or development of material sources from human activities. The total river basin area directly affected by human activities is of the same order of magnitude (>40 Mkm2) as the total area affected over the last 18 000 years. A tentative analysis of 38 major river systems totaling 55 Mkm2 is proposed for several criteria: (i) trajectories of Holocene evolution, (ii) occurrence of natural fluvial filters, (iii) present-day fluvial filters: most river basins are unique. Riverine fluxes per unit area are characterized by hot spots that exceed the world average by one order of magnitude. At the Anthropocene (i.e., since 1950), many riverine fluxes have globally increased (sodium, chloride, sulfate, nitrogen, phosphorous, heavy metals), others are stable (calcium, bicarbonate, sediments) or likely to decrease (dissolved silica). Future trajectories of river fluxes will depend on the balance between increased sources of material (e.g., soil erosion, pollution, fertilization), water abstraction for irrigation and the modification of fluvial filters, particularly the occurrence of reservoirs that already intercept half of the water and store at least 30% of river sediment fluxes. In some river systems, retention actually exceeds material production and river fluxes are actually decreasing. These trajectories are specific to each river and to each type of river material. Megacities, mining and industrial districts can be considered as hot spots of contaminants fluxes, while major reservoirs are global-scale sinks for all particulates. Global picture should therefore be determined at a fine resolution, since regional differences in Anthropocene evolution of river fluxes may reach one order of magnitude, as illustrated for total nitrogen.” Michel Meybeck, Charles Vörösmarty, Comptes Rendus Geoscience, Volume 337, Issues 1–2, January–February 2005, Pages 107–123,

Global analysis of river systems: from Earth system controls to Anthropocene syndromes – Meybeck (2003) “Continental aquatic systems from rivers to the coastal zone are considered within two perspectives: (i) as a major link between the atmosphere, pedosphere, biosphere and oceans within the Earth system with its Holocene dynamics, and (ii) as water and aquatic biota resources progressively used and transformed by humans. Human pressures have now reached a state where the continental aquatic systems can no longer be considered as being controlled by only Earth system processes, thus defining a new era, the Anthropocene. Riverine changes, now observed at the global scale, are described through a first set of syndromes (flood regulation, fragmentation, sediment imbalance, neo–arheism, salinization, chemical contamination, acidification, eutrophication and microbial contamination) with their related causes and symptoms. These syndromes have direct influences on water uses, either positive or negative. They also modify some Earth system key functions such as sediment, water, nutrient and carbon balances, greenhouse gas emissions and aquatic biodiversity. Evolution of river syndromes over the past 2000 years is complex: it depends upon the stages of regional human development and on natural conditions, as illustrated here for the chemical contamination syndrome. River damming, eutrophication and generalized decrease of river flow due to irrigation are some of the other global features of river changes. Future management of river systems should also consider these long–term impacts on the Earth system.” Michel Meybeck, Phil. Trans. R. Soc. Lond. B 29 December 2003 vol. 358 no. 1440 1935-1955, doi: 10.1098/rstb.2003.1379. [Full text]

Geology of mankind – Crutzen (2002) “For the past three centuries, the effects of humans on the global environment have escalated. Because of these anthropogenic emissions of carbon dioxide, global climate may depart significantly from natural behaviour for many millennia to come. It seems appropriate to assign the term ‘Anthropocene’ to the present, in many ways human-dominated, geological epoch, supplementing the Holocene — the warm period of the past 10–12 millennia. The Anthropocene could be said to have started in the latter part of the eighteenth century, when analyses of air trapped in polar ice showed the beginning of growing global concentrations of carbon dioxide and methane.” Paul J. Crutzen, Nature 415, 23 (3 January 2002) | doi:10.1038/415023a. [Full text]

On the history of humans as geomorphic agents – Hooke (2000) “The human population has been increasing exponentially. Simultaneously, as digging sticks and antlers have given way to wooden plows, iron spades, steam shovels, and today’s huge excavators, our ability and motivation to modify the landscape by moving earth in construction and mining activities have also increased dramatically. As a consequence, we have now become arguably the premier geomorphic agent sculpting the landscape, and the rate at which we are moving earth is increasing exponentially. As hunter-gatherer cultures were replaced by agrarian societies to feed this expanding population, erosion from agricultural fields also, until recently, increased steadily. This constitutes an unintended additional human impact on the landscape.” Roger LeB. Hooke, Geology September, 2000 v. 28, no. 9, p. 843-846, doi: 10.1130/​0091-7613(2000)​28​2.0.CO;2. [Full text]

L’éxigence idéaliste et le fait de l’évolution – Le Roy (1927) A book where term “Noosphere” is used for Anthropocene. E. W. Berry, Science, New Series, Vol. 64, No. 1644 (Jul. 2, 1926), p. 16, DOI: 10.2307/1651728.

The Term Psychozoic – Berry (1926) No abstract. E. W. Berry, Science, New Series, Vol. 64, No. 1644 (Jul. 2, 1926), p. 16, DOI: 10.2307/1651728.

Elements of Geology – Le Conte (1879) A book where term “Psychozoic” is used for Anthropocene. Le Conte, J. Elements of Geology; D. Appleton & Co: New York, 1879. [Full text]

Corsa di Geologia – Stoppani (1873) A book where term “anthropozoic” is used for Anthropocene. From Crutzen (2002): “Mankind’s growing influence on the environment was recognized as long ago as 1873, when the Italian geologist Antonio Stoppani spoke about a “new telluric force which in power and universality may be compared to the greater forces of earth,” referring to the “anthropozoic era”.” Stoppani, A. Corsa di Geologia; Milan, 1873.

Posted in AGW evidence, Climate science | 2 Comments »

Papers on the role of the Sun in recent global warming

Posted by Ari Jokimäki on January 7, 2013

This list contains papers that on Sun’s role in the recent climate change. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative. Generally no papers simply reporting solar activity measurements are included (those papers will get their own list in future) or other solar activity related papers that do not discuss recent climate change. Also indirect solar effects are mainly left to their own lists (for example through geomagnetism). There already are separate lists for solar cycle length and cosmic rays.

UPDATE (September 3, 2013): Wang & Dickinson (2013) added. Thanks to JesusR for pointing it out.

Contribution of solar radiation to decadal temperature variability over land – Wang & Dickinson (2013) “Global air temperature has become the primary metric for judging global climate change. The variability of global temperature on a decadal timescale is still poorly understood. This paper examines further one suggested hypothesis, that variations in solar radiation reaching the surface (Rs) have caused much of the observed decadal temperature variability. Because Rs only heats air during the day, its variability is plausibly related to the variability of diurnal temperature range (daily maximum temperature minus its minimum). We show that the variability of diurnal temperature range is consistent with the variability of Rs at timescales from monthly to decadal. This paper uses long comprehensive datasets for diurnal temperature range to establish what has been the contribution of Rs to decadal temperature variability. It shows that Rs over land globally peaked in the 1930s, substantially decreased from the 1940s to the 1970s, and changed little after that. Reduction of Rs caused a reduction of more than 0.2 °C in mean temperature during May to October from the 1940s through the 1970s, and a reduction of nearly 0.2 °C in mean air temperature during November to April from the 1960s through the 1970s. This cooling accounts in part for the near-constant temperature from the 1930s into the 1970s. Since then, neither the rapid increase in temperature from the 1970s through the 1990s nor the slowdown of warming in the early twenty-first century appear to be significantly related to changes of Rs.” Kaicun Wang and Robert E. Dickinson, PNAS, 2013, doi: 10.1073/pnas.1311433110. [Full text]

Evidence of recent causal decoupling between solar radiation and global temperature – Pasini et al. (2012) “The Sun has surely been a major external forcing to the climate system throughout the Holocene. Nevertheless, opposite trends in solar radiation and temperatures have been empirically identified in the last few decades. Here, by means of an inferential method—the Granger causality analysis—we analyze this situation and, for the first time, show that an evident causal decoupling between total solar irradiance and global temperature has appeared since the 1960s.” Antonello Pasini et al 2012 Environ. Res. Lett. 7 034020 doi:10.1088/1748-9326/7/3/034020. [Full text]

Solar Influence on Global and Regional Climates – Lockwood (2012) “The literature relevant to how solar variability influences climate is vast—but much has been based on inadequate statistics and non-robust procedures. The common pitfalls are outlined in this review. The best estimates of the solar influence on the global mean air surface temperature show relatively small effects, compared with the response to anthropogenic changes (and broadly in line with their respective radiative forcings). However, the situation is more interesting when one looks at regional and season variations around the global means. In particular, recent research indicates that winters in Eurasia may have some dependence on the Sun, with more cold winters occurring when the solar activity is low. Advances in modelling “top-down” mechanisms, whereby stratospheric changes influence the underlying troposphere, offer promising explanations of the observed phenomena. In contrast, the suggested modulation of low-altitude clouds by galactic cosmic rays provides an increasingly inadequate explanation of observations.” Mike Lockwood, Surveys in Geophysics, July 2012, Volume 33, Issue 3-4, pp 503-534. [Full text]

Solar Forcing of Climate – de Jager (2012) “Solar activity is evident both in the equatorial activity centres and in the polar magnetic field variations. The total solar irradiance variation is due to the former component. During the extraordinarily long minimum of activity between sunspot cycles 23 and 24, the variations related to the equatorial field components reached their minimum values in the first half of 2008, while those related to the polar field variations had their extreme values rather at the end of 2009 and the first half of 2010. The explanation of this delay is another challenge for dynamo theories. The role of the open solar flux has so far been grossly underestimated in discussions of Sun-climate relations. The gradual increase in the average terrestrial ground temperature since 1610 is related both to the equatorial and polar field variations. The main component (0.077 K/century) is due to the variation of the total solar irradiance. The second component (0.040 K/century) waits for an explanation. The smoothed residual increase, presumably antropogenic, obtained after subtraction of the known components from the total increase was 0.31 K in 1999.” C. de Jager, Surveys in Geophysics, July 2012, Volume 33, Issue 3-4, pp 445-451. [Full text]

Solar activity–climate relations: A different approach – Stauning (2011) “The presentation of solar activity–climate relations is extended with the most recent sunspot and global temperature data series. The extension of data series shows clearly that the changes in terrestrial temperatures are related to sources different from solar activity after ∼1985. Based on analyses of data series for the years 1850–1985 it is demonstrated that, apart from an interval of positive deviation followed by a similar negative excursion in Earth’s temperatures between ∼1923 and 1965, there is a strong correlation between solar activity and terrestrial temperatures delayed by 3 years, which complies with basic causality principles. A regression analysis between solar activity represented by the cycle-average sunspot number, SSNA, and global temperature anomalies, ΔTA, averaged over the same interval lengths, but delayed by 3 years, provides the relation ΔTA∼0.009 (±0.002) SSNA. Since the largest ever observed SSNA is ∼90 (in 1954–1965), the solar activity-related changes in global temperatures could amount to no more than ±0.4 °C over the past ∼400 years where the sunspots have been recorded. It is demonstrated that the small amplitudes of cyclic variations in the average global temperatures over the ∼11 year solar cycle excludes many of the various driver processes suggested in published and frequently quoted solar activity–climate relations. It is suggested that the in-cycle variations and also the longer term variations in global temperatures over the examined 135 years are mainly caused by corresponding changes in the total solar irradiance level representing the energy output from the core, but further modulated by varying energy transmission properties in the active outer regions of the Sun.” P. Stauning, Journal of Atmospheric and Solar-Terrestrial Physics, Volume 73, Issue 13, August 2011, Pages 1999–2012,

Are secular correlations between sunspots, geomagnetic activity, and global temperature significant? – Love et al. (2011) “Recent studies have led to speculation that solar-terrestrial interaction, measured by sunspot number and geomagnetic activity, has played an important role in global temperature change over the past century or so. We treat this possibility as an hypothesis for testing. We examine the statistical significance of cross-correlations between sunspot number, geomagnetic activity, and global surface temperature for the years 1868–2008, solar cycles 11–23. The data contain substantial autocorrelation and nonstationarity, properties that are incompatible with standard measures of cross-correlational significance, but which can be largely removed by averaging over solar cycles and first-difference detrending. Treated data show an expected statistically-significant correlation between sunspot number and geomagnetic activity, Pearson p < 10−4, but correlations between global temperature and sunspot number (geomagnetic activity) are not significant, p = 0.9954, (p = 0.8171). In other words, straightforward analysis does not support widely-cited suggestions that these data record a prominent role for solar-terrestrial interaction in global climate change. With respect to the sunspot-number, geomagnetic-activity, and global-temperature data, three alternative hypotheses remain difficult to reject: (1) the role of solar-terrestrial interaction in recent climate change is contained wholly in long-term trends and not in any shorter-term secular variation, or, (2) an anthropogenic signal is hiding correlation between solar-terrestrial variables and global temperature, or, (3) the null hypothesis, recent climate change has not been influenced by solar-terrestrial interaction.” Love, J. J., K. Mursula, V. C. Tsai, and D. M. Perkins (2011), Geophys. Res. Lett., 38, L21703, doi:10.1029/2011GL049380. [Full text]

Solar influences on climate – Gray et al. (2010) “Understanding the influence of solar variability on the Earth’s climate requires knowledge of solar variability, solar-terrestrial interactions, and the mechanisms determining the response of the Earth’s climate system. We provide a summary of our current understanding in each of these three areas. Observations and mechanisms for the Sun’s variability are described, including solar irradiance variations on both decadal and centennial time scales and their relation to galactic cosmic rays. Corresponding observations of variations of the Earth’s climate on associated time scales are described, including variations in ozone, temperatures, winds, clouds, precipitation, and regional modes of variability such as the monsoons and the North Atlantic Oscillation. A discussion of the available solar and climate proxies is provided. Mechanisms proposed to explain these climate observations are described, including the effects of variations in solar irradiance and of charged particles. Finally, the contributions of solar variations to recent observations of global climate change are discussed.” Gray, L. J., et al. (2010), SOLAR INFLUENCES ON CLIMATE, Rev. Geophys., 48, RG4001, doi:10.1029/2009RG000282. [Full text]

An influence of solar spectral variations on radiative forcing of climate – Haigh et al. (2010) “The thermal structure and composition of the atmosphere is determined fundamentally by the incoming solar irradiance. Radiation at ultraviolet wavelengths dissociates atmospheric molecules, initiating chains of chemical reactions—specifically those producing stratospheric ozone—and providing the major source of heating for the middle atmosphere, while radiation at visible and near-infrared wavelengths mainly reaches and warms the lower atmosphere and the Earth’s surface. Thus the spectral composition of solar radiation is crucial in determining atmospheric structure, as well as surface temperature, and it follows that the response of the atmosphere to variations in solar irradiance depends on the spectrum. Daily measurements of the solar spectrum between 0.2 µm and 2.4 µm, made by the Spectral Irradiance Monitor (SIM) instrument on the Solar Radiation and Climate Experiment (SORCE) satellite since April 2004, have revealed that over this declining phase of the solar cycle there was a four to six times larger decline in ultraviolet than would have been predicted on the basis of our previous understanding. This reduction was partially compensated in the total solar output by an increase in radiation at visible wavelengths. Here we show that these spectral changes appear to have led to a significant decline from 2004 to 2007 in stratospheric ozone below an altitude of 45 km, with an increase above this altitude. Our results, simulated with a radiative-photochemical model, are consistent with contemporaneous measurements of ozone from the Aura-MLS satellite, although the short time period makes precise attribution to solar effects difficult. We also show, using the SIM data, that solar radiative forcing of surface climate is out of phase with solar activity. Currently there is insufficient observational evidence to validate the spectral variations observed by SIM, or to fully characterize other solar cycles, but our findings raise the possibility that the effects of solar variability on temperature throughout the atmosphere may be contrary to current expectations.” Joanna D. Haigh, Ann R. Winning, Ralf Toumi & Jerald W. Harder, Nature, Volume: 467, Pages: 696–699, Date published: 07 October 2010, doi:10.1038/nature09426. [Full text]

Solar change and climate: an update in the light of the current exceptional solar minimum – Lockwood (2010) “Solar outputs during the current solar minimum are setting record low values for the space age. Evidence is here reviewed that this is part of a decline in solar activity from a grand solar maximum and that the Sun has returned to a state that last prevailed in 1924. Recent research into what this means, and does not mean, for climate change is reviewed.” Mike Lockwood, Proc. R. Soc. A 8 February 2010 vol. 466 no. 2114 303-329, doi: 10.1098/rspa.2009.0519. [Full text]

Cycles and trends in solar irradiance and climate – Lean (2010) “How—indeed whether—the Sun’s variable energy outputs influence Earth’s climate has engaged scientific curiosity for more than a century. Early evidence accrued from correlations of assorted solar and climate indices, and from recognition that cycles near 11, 88 and 205 years are common in both the Sun and climate. But until recently, an influence of solar variability on climate, whether through cycles or trends, was usually dismissed because climate simulations with (primarily) simple energy balance models indicated that responses to the decadal solar cycle would be so small as to be undetectable in observations. However, in the past decade modeling studies have found both resonant responses and positive feedbacks in the ocean‐atmosphere system that may amplify the response to solar irradiance variations. Today, solar cycles and trends are recognized as important components of natural climate variability on decadal to centennial time scales. Understanding solar‐terrestrial linkages is requisite for the comprehensive understanding of Earth’s evolving environment. The attribution of present‐day climate change, interpretation of changes prior to the industrial epoch, and forecast of future decadal climate change necessitate quantitative understanding of how, when, where, and why natural variability, including by the Sun, may exceed, obscure or mitigate anthropogenic changes.” Judith L. Lean, Wiley Interdisciplinary Reviews: Climate Change, 1, 1, 111-122, DOI: 10.1002/wcc.18. [Full text]

Solar trends and global warming – Benestad & Schmidt (2009) “We use a suite of global climate model simulations for the 20th century to assess the contribution of solar forcing to the past trends in the global mean temperature. In particular, we examine how robust different published methodologies are at detecting and attributing solar-related climate change in the presence of intrinsic climate variability and multiple forcings. We demonstrate that naive application of linear analytical methods such as regression gives nonrobust results. We also demonstrate that the methodologies used by Scafetta and West (2005, 2006a, 2006b, 2007, 2008) are not robust to these same factors and that their error bars are significantly larger than reported. Our analysis shows that the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.” Benestad, R. E. and G. A. Schmidt (2009), Solar trends and global warming, J. Geophys. Res., 114, D14101, doi:10.1029/2008JD011639. [Full text]

Recent changes in solar outputs and the global mean surface temperature. III. Analysis of contributions to global mean air surface temperature rise – Lockwood (2008) “A multivariate fit to the variation in global mean surface air temperature anomaly over the past half century is presented. The fit procedure allows for the effect of response time on the waveform, amplitude and lag of each radiative forcing input, and each is allowed to have its own time constant. It is shown that the contribution of solar variability to the temperature trend since 1987 is small and downward; the best estimate is −1.3% and the 2σ confidence level sets the uncertainty range of −0.7 to −1.9%. The result is the same if one quantifies the solar variation using galactic cosmic ray fluxes (for which the analysis can be extended back to 1953) or the most accurate total solar irradiance data composite. The rise in the global mean air surface temperatures is predominantly associated with a linear increase that represents the combined effects of changes in anthropogenic well-mixed greenhouse gases and aerosols, although, in recent decades, there is also a considerable contribution by a relative lack of major volcanic eruptions. The best estimate is that the anthropogenic factors contribute 75% of the rise since 1987, with an uncertainty range (set by the 2σ confidence level using an AR(1) noise model) of 49–160%; thus, the uncertainty is large, but we can state that at least half of the temperature trend comes from the linear term and that this term could explain the entire rise. The results are consistent with the intergovernmental panel on climate change (IPCC) estimates of the changes in radiative forcing (given for 1961–1995) and are here combined with those estimates to find the response times, equilibrium climate sensitivities and pertinent heat capacities (i.e. the depth into the oceans to which a given radiative forcing variation penetrates) of the quasi-periodic (decadal-scale) input forcing variations. As shown by previous studies, the decadal-scale variations do not penetrate as deeply into the oceans as the longer term drifts and have shorter response times. Hence, conclusions about the response to century-scale forcing changes (and hence the associated equilibrium climate sensitivity and the temperature rise commitment) cannot be made from studies of the response to shorter period forcing changes.” Mike Lockwood, Proc. R. Soc. A 8 June 2008 vol. 464 no. 2094 1387-1404, doi: 10.1098/rspa.2007.0348. [Full text]

Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature. II. Different reconstructions of the total solar irradiance variation and dependence on response time scale – Lockwood & Fröhlich (2008) “We have previously placed the solar contribution to recent global warming in context using observations and without recourse to climate models. It was shown that all solar forcings of climate have declined since 1987. The present paper extends that analysis to include the effects of the various time constants with which the Earth’s climate system might react to solar forcing. The solar input waveform over the past 100 years is defined using observed and inferred galactic cosmic ray fluxes, valid for either a direct effect of cosmic rays on climate or an effect via their known correlation with total solar irradiance (TSI), or for a combination of the two. The implications, and the relative merits, of the various TSI composite data series are discussed and independent tests reveal that the PMOD composite used in our previous paper is the most realistic. Use of the ACRIM composite, which shows a rise in TSI over recent decades, is shown to be inconsistent with most published evidence for solar influences on pre-industrial climate. The conclusions of our previous paper, that solar forcing has declined over the past 20 years while surface air temperatures have continued to rise, are shown to apply for the full range of potential time constants for the climate response to the variations in the solar forcings.” Mike Lockwood and Claus Fröhlich, Proc. R. Soc. A 8 June 2008 vol. 464 no. 2094 1367-1385, doi: 10.1098/rspa.2007.0347. [Full text]

Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature – Lockwood & Fröhlich (2007) “There is considerable evidence for solar influence on the Earth’s pre-industrial climate and the Sun may well have been a factor in post-industrial climate change in the first half of the last century. Here we show that over the past 20 years, all the trends in the Sun that could have had an influence on the Earth’s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures.” Mike Lockwood and Claus Fröhlich, Proc. R. Soc. A 8 October 2007 vol. 463 no. 2086 2447-2460, doi: 10.1098/rspa.2007.1880. [Full text]

Variations in solar luminosity and their effect on the Earth’s climate – Foukal et al. (2006) “Variations in the Sun’s total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change, and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century. Additional climate forcing by changes in the Sun’s output of ultraviolet light, and of magnetized plasmas, cannot be ruled out. The suggested mechanisms are, however, too complex to evaluate meaningfully at present.” P. Foukal, C. Fröhlich, H. Spruit and T. M. L. Wigley, Nature 443, 161-166 (14 September 2006) | doi:10.1038/nature05072. [Full text]

Phenomenological solar contribution to the 1900–2000 global surface warming – Scafetta & West (2006) “We study the role of solar forcing on global surface temperature during four periods of the industrial era (1900–2000, 1900–1950, 1950–2000 and 1980–2000) by using a sun-climate coupling model based on four scale-dependent empirical climate sensitive parameters to solar variations. We use two alternative total solar irradiance satellite composites, ACRIM and PMOD, and a total solar irradiance proxy reconstruction. We estimate that the sun contributed as much as 45–50% of the 1900–2000 global warming, and 25–35% of the 1980–2000 global warming. These results, while confirming that anthropogenic-added climate forcing might have progressively played a dominant role in climate change during the last century, also suggest that the solar impact on climate change during the same period is significantly stronger than what some theoretical models have predicted.” Scafetta, N. and B. J. West (2006), Phenomenological solar contribution to the 1900–2000 global surface warming, Geophys. Res. Lett., 33, L05708, doi:10.1029/2005GL025539. [Full text]

Measurement and Uncertainty of the Long-Term Total Solar Irradiance Trend – Dewitte et al. (2005) “A possible long-term trend of the total solar irradiance could be a natural cause for climate variations on Earth. Measurement of the total solar irradiance with space radiometers started in 1978. We present a new total solar irradiance composite, with an uncertainty of ± 0.35 W m−2. From the minimum in 1995 to the maximum in 2002 the total solar irradiance increased by 1.6 W m−2. In between the minima of 1987 and 1995 the total solar irradiance increased by 0.15 W m−2.” Steven Dewitte, Dominique Crommelynck, Sabri Mekaoui, Alexandre Joukoff, Solar Physics, October 2004, Volume 224, Issue 1-2, pp 209-216, DOI: 10.1007/s11207-005-5698-7. [Full text]

Total solar irradiance and climate – Mendoza (2005) “The solar radiation is the fundamental source of energy that drives the Earth’s climate and sustains life. The variability of this output certainly affects our planet. In the last two decades an enormous advance in the understanding of the variability of the solar irradiance has been achieved. Space-based measurements indicate that the total solar irradiance changes at various time scales, from minutes to the solar cycle. Climate models show that total solar irradiance variations can account for a considerable part of the temperature variation of the Earth’s atmosphere in the pre-industrial era. During the 20th century its relative influence on the temperature changes has descended considerably. This means that other sources of solar activity as well as internal and man-made causes are contributing to the Earth’s temperature variability, particularly the former in the 20th century. Some very challenging questions concerning total solar irradiance variations and climate have been raised: are total solar irradiance variations from cycle to cycle well represented by sunspot and facular changes? Does total solar irradiance variations always parallel the solar activity cycle? Is there a long-term variation of the total solar irradiance, and closely related to this, is the total solar irradiance output of the quiet sun constant? If there is not a long-term trend of total solar irradiance variations, then we need amplifying mechanisms of total solar irradiance to account for the good correlations found between total solar irradiance and climate. The latter because the observed total solar irradiance changes are inconsequential when introduced in present climate models.” Blanca Mendoza, Advances in Space Research, Volume 35, Issue 5, 2005, Pages 882–890, [Full text]

How unusual is today’s solar activity? (reply) – Solanki et al. (2005) “Muscheler et al. claim that the solar activity affecting cosmic rays was much higher in the past than we deduced from 14C measurements. However, this claim is based on a problematic normalization and is in conflict with independent results, such as the 44Ti activity in meteorites and the 10Be concentration in ice cores.” S. K. Solanki, I. G. Usoskin, B. Kromer, M. Schüssler & J. Beer, Nature 436, E4-E5 (28 July 2005) | doi:10.1038/nature04046.

How unusual is today’s solar activity? – Muscheler et al. (2005) “To put global warming into context requires knowledge about past changes in solar activity and the role of the Sun in climate change. Solanki et al. propose that solar activity during recent decades was exceptionally high compared with that over the preceding 8,000 years. However, our extended analysis of the radiocarbon record reveals several periods during past centuries in which the strength of the magnetic field in the solar wind was similar to, or even higher than, that of today.” Raimund Muscheler, Fortunat Joos, Simon A. Müller & Ian Snowball, Nature 436, E3-E4 (28 July 2005) | doi:10.1038/nature04045.

Unusual activity of the Sun during recent decades compared to the previous 11,000 years – Solanki et al. (2004) “Direct observations of sunspot numbers are available for the past four centuries, but longer time series are required, for example, for the identification of a possible solar influence on climate and for testing models of the solar dynamo. Here we report a reconstruction of the sunspot number covering the past 11,400 years, based on dendrochronologically dated radiocarbon concentrations. We combine physics-based models for each of the processes connecting the radiocarbon concentration with sunspot number. According to our reconstruction, the level of solar activity during the past 70 years is exceptional, and the previous period of equally high activity occurred more than 8,000 years ago. We find that during the past 11,400 years the Sun spent only of the order of 10% of the time at a similarly high level of magnetic activity and almost all of the earlier high-activity periods were shorter than the present episode. Although the rarity of the current episode of high average sunspot numbers may indicate that the Sun has contributed to the unusual climate change during the twentieth century, we point out that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades.” S. K. Solanki, I. G. Usoskin, B. Kromer, M. Schüssler & J. Beer, Nature 431, 1084-1087 (28 October 2004) | doi:10.1038/nature02995.

Can solar variability explain global warming since 1970? – Solanki & Krivova (2003) “The magnitude of the Sun’s influence on climate has been a subject of intense debate. Estimates of this magnitude are generally based on assumptions regarding the forcing due to solar irradiance variations and climate modeling. This approach suffers from uncertainties that are difficult to estimate. Such uncertainties are introduced because the employed models may not include important but complex processes or mechanisms or may treat these in too simplified a manner. Here we take a more empirical approach. We employ time series of the most relevant solar quantities, the total and UV irradiance between 1856 and 1999 and the cosmic rays flux between 1868 and 1999. The time series are constructed using direct measurements wherever possible and reconstructions based on models and proxies at earlier times. These time series are compared with the climate record for the period 1856 to 1970. The solar records are scaled such that statistically the solar contribution to climate is as large as possible in this period. Under this assumption we repeat the comparison but now including the period 1970–1999. This comparison shows without requiring any recourse to modeling that since roughly 1970 the solar influence on climate (through the channels considered here) cannot have been dominant. In particular, the Sun cannot have contributed more than 30% to the steep temperature increase that has taken place since then, irrespective of which of the three considered channels is the dominant one determining Sun-climate interactions: tropospheric heating caused by changes in total solar irradiance, stratospheric chemistry influenced by changes in the solar UV spectrum, or cloud coverage affected by the cosmic ray flux.” Solanki, S. K. and N. A. Krivova (2003), Can solar variability explain global warming since 1970?, J. Geophys. Res., 108(A5), 1200, doi:10.1029/2002JA009753. [Full text]

Do Models Underestimate the Solar Contribution to Recent Climate Change? – Stott et al. (2003) “Current attribution analyses that seek to determine the relative contributions of different forcing agents to observed near-surface temperature changes underestimate the importance of weak signals, such as that due to changes in solar irradiance. Here a new attribution method is applied that does not have a systematic bias against weak signals. It is found that current climate models underestimate the observed climate response to solar forcing over the twentieth century as a whole, indicating that the climate system has a greater sensitivity to solar forcing than do models. The results from this research show that increases in solar irradiance are likely to have had a greater influence on global-mean temperatures in the first half of the twentieth century than the combined effects of changes in anthropogenic forcings. Nevertheless the results confirm previous analyses showing that greenhouse gas increases explain most of the global warming observed in the second half of the twentieth century.” Stott, Peter A., Gareth S. Jones, John F. B. Mitchell, 2003: Do Models Underestimate the Solar Contribution to Recent Climate Change?. J. Climate, 16, 4079–4093. doi:;2. [Full text]

The Sun’s Role in Climate Variations – Rind (2002) A review paper. “Is the Sun the controller of climate changes, only the instigator of changes that are mostly forced by the system feedbacks, or simply a convenient scapegoat for climate variations lacking any other obvious cause? This question is addressed for suggested solar forcing mechanisms operating on time scales from billions of years to decades. Each mechanism fails to generate the expected climate response in important respects, although some relations are found. The magnitude of the system feedbacks or variability appears as large or larger than that of the solar forcing, making the Sun’s true role ambiguous. As the Sun provides an explicit external forcing, a better understanding of its cause and effect in climate change could help us evaluate the importance of other climate forcings (such as past and future greenhouse gas changes).” D. Rind, Science 26 April 2002: Vol. 296 no. 5568 pp. 673-677, DOI: 10.1126/science.1069562. [Full text]

The effects of solar variability on the Earth’s climate – Haigh (2002) A review paper. “The absolute value of total solar irradiance is not known to better than ca. 0.3% but measurements from satellite instruments over the past two solar cycles have shown that it varies by ca. 0.1% on this time-scale. Over longer periods its value has been reconstructed using proxy measures of solar activity, and these suggest that during the Maunder minimum in solar activity of the late 17th century it was 3-4 W m-2 lower than at present. Observational data suggest that the Sun has influenced temperatures on decadal, centennial and millennial time-scales, but radiative forcing considerations and the results of energy-balance models and general circulation models suggest that the warming during the latter part of the 20th century cannot be ascribed entirely to solar effects. However, chemical and dynamical processes in the middle atmosphere may act to amplify the solar impact. An analysis of zonal mean temperature data shows that solar effects may be differentiated from those associated with other factors such as volcanic eruptions and the El Niño Southern Oscillation.” Joanna D. Haigh, Philosophical Transactions: Mathematical, Physical and Engineering Sciences, Vol. 361, No. 1802, Science and Applications of the Space Environment: New Results and Interdisciplinary Connections (Jan. 15, 2003), pp. 95-111. [Full text]

Solar Variability and the Earth’s Climate: Introduction and Overview – Reid (2000) “Numerous attempts have been made over the years to link various aspects of solar variability to changes in the Earth’s climate. There has been growing interest in this possible connection in recent years, spurred largely by the need to understand the natural causes of climate change, against which the expected global warming due to man’s activities will have to be detected. The time scale of concern here is that of decades to centuries, and excludes the longer millennial scale in which orbital variations play a dominant role. The field has long been plagued by the lack of an acceptable physical mechanism by which solar variability can affect climate, but the discovery of variability in the Sun’s total irradiance (the solar “constant” of meteorology) by spacecraft instruments has pointed to a direct mechanism. Other less direct mechanisms that have been suggested involve variations in the Sun’s ultraviolet flux and in the plasma outflow of the solar wind. The purpose of this paper is to summarize the current state of the field, emphasizing the proposed mechanisms as an introduction to the more detailed papers that follow. The particular case of sea-surface temperature data will be used as an illustration.” George C. Reid, Space Science Reviews, November 2000, Volume 94, Issue 1-2, pp 1-11, DOI: 10.1023/A:1026797127105.

The Sun’s total irradiance: Cycles, trends and related climate change uncertainties since 1976 – Fröhlich & Lean (1998) “A composite record of the Sun’s total irradiance compiled from measurements made by five independent space‐based radiometers since 1978 exhibits a prominent 11‐year cycle with similar levels during 1986 and 1996, the two most recent minimum epochs of solar activity. This finding contradicts recent assertions of a 0.04% irradiance increase from the 1986 to 1996 solar minima and suggests that solar radiative output trends contributed little of the 0.2°C increase in the global mean surface temperature in the past decade. Nor does our 18‐year composite irradiance record support a recent upward irradiance trend inferred from solar cycle length, a parameter used to imply a close linkage in the present century between solar variability and climate change.” Fröhlich, C. and J. Lean (1998), The Sun’s total irradiance: Cycles, trends and related climate change uncertainties since 1976, Geophys. Res. Lett., 25(23), 4377–4380, doi:10.1029/1998GL900157. [Full text]

Dependence of global temperatures on atmospheric CO2 and solar irradiance – Thomson (1997) “Changes in global average temperatures and of the seasonal cycle are strongly coupled to the concentration of atmospheric CO2. I estimate transfer functions from changes in atmospheric CO2 and from changes in solar irradiance to hemispheric temperatures that have been corrected for the effects of precession. They show that changes from CO2 over the last century are about three times larger than those from changes in solar irradiance. The increase in global average temperature during the last century is at least 20 times the SD of the residual temperature series left when the effects of CO2 and changes in solar irradiance are subtracted.” David J. Thomson, PNAS August 5, 1997 vol. 94 no. 16 8370-8377. [Full text]

The Seasons, Global Temperature, and Precession – Thomson (1995) “Analysis of instrumental temperature records beginning in 1659 shows that in much of the world the dominant frequency of the seasons is one cycle per anomalistic year (the time from perihelion to perihelion, 365.25964 days), not one cycle per tropical year (the time from equinox to equinox, 365.24220 days), and that the timing of the annual temperature cycle is controlled by perihelion. The assumption that the seasons were timed by the equinoxes has caused many statistical analyses of climate data to be badly biased. Coherence between changes in the amplitude of the annual cycle and those in the average temperature show that between 1854 and 1922 there were small temperature variations, probably of solar origin. Since 1922, the phase of the Northern Hemisphere coherence between these quantities switched from 0° to 180° and implies that solar variability cannot be the sole cause of the increasing temperature over the last century. About 1940, the phase patterns of the previous 300 years began to change and now appear to be changing at an unprecedented rate. The average change in phase is now coherent with the logarithm of atmospheric CO2 concentration.” David J. Thomson, Science 7 April 1995: Vol. 268 no. 5207 pp. 59-68, DOI: 10.1126/science.268.5207.59.

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Climate skeptic claims prebunked by Keeling

Posted by Ari Jokimäki on August 23, 2012

If you have followed discussions about global warming, you probably have seen claims that because atmospheric carbon dioxide concentration is measured on the top of a volcano (actually on the side – the measurement station is at the elevation of 3400m while the top of the mountain is at the elevation of over 4100m), and that volcanos emit carbon dioxide, the carbon dioxide measurements cannot be trusted.  Thus the argument concludes that we don’t know if atmospheric carbon dioxide concentration is rising or not. Here we take a look at what Charles David Keeling (1928 – 2005) wrote long ago.

Charles David Keeling in the lab

As many of you probably know, Keeling was the one who arranged atmospheric carbon dioxide measurements starting in the 1950s, that resulted in the famous Keeling Curve, which describes the evolution of atmospheric carbon dioxide as measured in Hawaii, on top of a volcano called Mauna Loa. The measurement site was selected, because Hawaii is located in the middle of an ocean and far away from disturbing carbon dioxide sources. Also, the elevation of the location of the station ensures that measured air masses are representative of large areas. However, as the Keeling Curve is famous and is drawn from the measurements that originate at a site that has volcanic vents nearby, it is quite natural that there are claims made that the presence of the volcano somehow invalidates all our knowledge of atmospheric carbon dioxide. Many readers of course know that it isn’t so, but here we look at what Keeling wrote about the issue in 1960. It turns out he had already debunked the claims, even before those claims were made.

In 1960, Keeling published the paper The Concentration and Isotopic Abundances of Carbon Dioxide in the Atmosphere (full text freely available in the linked abstract page). In this paper he discussed results from carbon dioxide measurements during a few years of observtions. Early in the paper he says:

“Three gas analysers, as described by SMITH (1953), equipped with strip chart recorders, have been employed to measure the concentration of carbon dioxide continuously at stations in Antarctica, Hawaii, and California.”

So already from the beginning of Keeling’s measurements there were other measurement stations besides Mauna Loa. End of story? Well, pretty much so for those claims, but anyway, let’s take a look at what other things Keeling has to say on the subject.

Despite the reality, what if Mauna Loa was the only atmospheric carbon dioxide measuring station as those claims suggest? Would carbon dioxide measurements be suspect because of that? Keeling discusses this too. Keeling notes that there was local contamination in all of the measurement stations. In the Antarctica station there was some combustion of fuel near the station:

“It could be readily spotted from the significant fluctuations in the otherwise steady trace of the recorder pen and was eliminated from consideration in the initial reading of the charts.”

In Mauna Loa, there also was some extra variability in the measurement record:

“This is attributed to release of carbon dioxide by nearby volcanic vents; combustion on the island associated with agricultural, industrial, and domestic activities; and lower concentration of carbon dioxide in the air transported to the station by upslope winds.”

It seems that Keeling was well aware that “Mauna Loa is a volcano”. He also identified some other sources of contamination. Not only was Keeling aware of the situation, he also knew how to correct it:

“The values reported here are averages of data for periods of downslope winds or strong lateral winds when the concentration remained nearly constant for several hours or more.”

At a California measurement station there was an interesting situation. The measured carbon dioxide concentration was found to be highly variable:

“Highest concentrations occur during light winds from the north, from the direction of Los Angeles; lowest concentrations when the wind is from the west or southwest and of moderate force or greater.”

Highest concentrations when winds were blowing from a large city? Why is that? Could it be that there is carbon dioxide coming from human actions?

Keeling then proceeds to discuss seasonal variation which he finds in the Northern Hemisphere but not in the Southern Hemisphere. Based on carbon-13 measurements, he concludes that the seasonal variation found in the Northern Hemisphere is from the activity of land plants. He also notes that timing of maximum and minimum concentrations match the timing of the land vegetation activity in the Northern Hemisphere. Keeling explains the absence of seasonal variability in the Southern Hemisphere by the smaller area of vegetation in the Southern Hemisphere.

Getting back to the claims of CO2 record contamination, Keeling then discusses the interannual trends in carbon dioxide concentration:

“Where data extend beyond one year, averages for the second year are higher than for the first year. At the South Pole, where the longest record exists, the concentration has increased at the rate of about 1.3 p.p.m. per year.”

Note that Keeling reported the first clear increase in carbon dioxide concentration from the South Pole, not from Mauna Loa.

So, already back in 1960, Keeling knew that Mauna Loa was a volcano. He also knew how to correct the problems that the volcano caused for carbon dioxide measurements. He also knew that the volcanic problems wouldn’t matter anyway because there were other measurement stations that were nowhere near any volcanos, and those stations show the same thing as Mauna Loa station – atmospheric carbon dioxide concentration is rising.

Posted in AGW evidence, Climate claims, Climate science | 3 Comments »

Papers on last interglacial climate

Posted by Ari Jokimäki on June 21, 2012

This is a list of papers on last interglacial (so called Eemian interglacial, between about 130000 and 110000 years ago) climate conditions with emphasis on papers that discuss last interglacial as an indicator of future climate conditions and consequences. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

European climate optimum and enhanced Greenland melt during the Last Interglacial – Goñi et al. (2012) “The Last Interglacial climatic optimum, ca. 128 ka, is the most recent climate interval significantly warmer than present, providing an analogue (albeit imperfect) for ongoing global warming and the effects of Greenland Ice Sheet (GIS) melting on climate over the coming millennium. While some climate models predict an Atlantic meridional overturning circulation (AMOC) strengthening in response to GIS melting, others simulate weakening, leading to cooling in Europe. Here, we present evidence from new proxy-based paleoclimate and ocean circulation reconstructions that show that the strongest warming in western Europe coincided with maximum GIS meltwater runoff and a weaker AMOC early in the Last Interglacial. By performing a series of climate model sensitivity experiments, including enhanced GIS melting, we were able to simulate this configuration of the Last Interglacial climate system and infer information on AMOC slowdown and related climate effects. These experiments suggest that GIS melt inhibited deep convection off the southern coast of Greenland, cooling local climate and reducing AMOC by ∼24% of its present strength. However, GIS melt did not perturb overturning in the Nordic Seas, leaving heat transport to, and thereby temperatures in, Europe unaffected.” Maria Fernanda Sánchez Goñi, Pepijn Bakker, Stéphanie Desprat, Anders E. Carlson, Cédric J. Van Meerbeeck, Odile Peyron, Filipa Naughton, William J. Fletcher, Frédérique Eynaud, Linda Rossignol and Hans Renssen, Geology, v. 40 no. 7 p. 627-630, doi: 10.1130/G32908.1. [FULL TEXT]

Sr-Nd-Pb Isotope Evidence for Ice-Sheet Presence on Southern Greenland During the Last Interglacial – Colville et al. (2012) “To ascertain the response of the southern Greenland Ice Sheet (GIS) to a boreal summer climate warmer than at present, we explored whether southern Greenland was deglaciated during the Last Interglacial (LIG), using the Sr-Nd-Pb isotope ratios of silt-sized sediment discharged from southern Greenland. Our isotope data indicate that no single southern Greenland geologic terrane was completely deglaciated during the LIG, similar to the Holocene. Differences in sediment sources during the LIG relative to the early Holocene denote, however, greater southern GIS retreat during the LIG. These results allow the evaluation of a suite of GIS models and are consistent with a GIS contribution of 1.6 to 2.2 meters to the ≥4-meter LIG sea-level highstand, requiring a significant sea-level contribution from the Antarctic Ice Sheet.” Elizabeth J. Colville, Anders E. Carlson, Brian L. Beard, Robert G. Hatfield, Joseph S. Stoner, Alberto V. Reyes, David J. Ullman, Science 29 July 2011: Vol. 333 no. 6042 pp. 620-623, DOI: 10.1126/science.1204673. [FULL TEXT]

Probabilistic assessment of sea level during the last interglacial stage – Kopp et al. (2009) “With polar temperatures ~3–5 °C warmer than today, the last interglacial stage (~125 kyr ago) serves as a partial analogue for 1–2 °C global warming scenarios. Geological records from several sites indicate that local sea levels during the last interglacial were higher than today, but because local sea levels differ from global sea level, accurately reconstructing past global sea level requires an integrated analysis of globally distributed data sets. Here we present an extensive compilation of local sea level indicators and a statistical approach for estimating global sea level, local sea levels, ice sheet volumes and their associated uncertainties. We find a 95% probability that global sea level peaked at least 6.6 m higher than today during the last interglacial; it is likely (67% probability) to have exceeded 8.0 m but is unlikely (33% probability) to have exceeded 9.4 m. When global sea level was close to its current level (≥-10 m), the millennial average rate of global sea level rise is very likely to have exceeded 5.6 m kyr-1 but is unlikely to have exceeded 9.2 m kyr-1. Our analysis extends previous last interglacial sea level studies by integrating literature observations within a probabilistic framework that accounts for the physics of sea level change. The results highlight the long-term vulnerability of ice sheets to even relatively low levels of sustained global warming.” Robert E. Kopp, Frederik J. Simons, Jerry X. Mitrovica, Adam C. Maloof & Michael Oppenheimer, Nature 462, 863-867 (17 December 2009) | doi:10.1038/nature08686. [Full text]

Response of the southern Greenland Ice Sheet during the last two deglaciations – Carlson et al. (2012) “The retreat of the southern Greenland Ice Sheet (GIS) during the last deglaciation (Termination I: TI) is poorly dated by conventional means; there is even greater uncertainty about the penultimate deglaciation (Termination II: TII), leading to the assumption that the southern GIS has a significant lag in its response to deglacial warming. Here we use geochemical terrestrial sediment proxies ([Fe] and [Ti]) from a well-studied southern Greenland marine sediment sequence to examine the behavior of the southern GIS during TI and TII. Our records show that during TI and TII the southern GIS response was essentially synchronous with deglacial North Atlantic warming, implying greater climate sensitivity than previously assumed. During TI, elevated ablation lasted ~5 k.y., whereas ablation remained elevated for ~12 k.y. during TII, suggesting a reduced southern GIS during TII that contributed a significant fraction of the higher sea level during the subsequent interglacial.” Anders E. Carlson, Joseph S. Stoner, Jeffrey P. Donnelly and Claude Hillaire-Marcel, Geology May 2008 v. 36, no. 5, p. 359-362, doi: 10.1130/​G24519A.1. [FULL TEXT]

The climate in Europe during the Eemian: a multi-method approach using pollen data – Brewer et al. (2008) “The Last Interglacial period, the Eemian, offers a testbed for comparing climate evolution throughout an interglacial with the current warm period. We present here results from climatic reconstructions from 17 sites distributed across the European continent, allowing an assessment of trends and regional averages of climate changes during this period. We use a multi-method approach to allow for an improved assessment of the uncertainties involved in the reconstruction. In addition, the method takes into account the errors associated with the age model. The resulting uncertainties are large, but allow a more robust assessment of the reconstructed climatic variations than in previous studies. The results show a traditional three-part Eemian, with an early optimum, followed by slight cooling and eventually a sharp drop in both temperatures and precipitation. This sequence is however, restricted to the north, as this latter change is not observed in the south where temperatures remain stable for longer. These variations led to marked variation in the latitudinal temperature gradient during the Eemian. The difference between the two regions is also noticeable in the magnitude of changes, with greater variations in the north than the south. Some evidence is found for changes in lapse rates, however, a greater number of sites is needed to confirm this.” S. Brewer, J. Guiot, M.F. Sánchez-Goñi, S. Klotz, Quaternary Science Reviews, Volume 27, Issues 25–26, December 2008, Pages 2303–2315,

The Deep Ocean During the Last Interglacial Period – Duplessy et al. (2007) “Oxygen isotope analysis of benthic foraminifera in deep sea cores from the Atlantic and Southern Oceans shows that during the last interglacial period, North Atlantic Deep Water (NADW) was 0.4° ± 0.2°C warmer than today, whereas Antarctic Bottom Water temperatures were unchanged. Model simulations show that this distribution of deep water temperatures can be explained as a response of the ocean to forcing by high-latitude insolation. The warming of NADW was transferred to the Circumpolar Deep Water, providing additional heat around Antarctica, which may have been responsible for partial melting of the West Antarctic Ice Sheet.” J. C. Duplessy, D. M. Roche and M. Kageyama, Science 6 April 2007: Vol. 316 no. 5821 pp. 89-91, DOI: 10.1126/science.1138582. [Full text]

Evidence for last interglacial chronology and environmental change from Southern Europe – Brauer et al. (2007) “Establishing phase relationships between earth-system components during periods of rapid global change is vital to understanding the underlying processes. It requires records of each component with independent and accurate chronologies. Until now, no continental record extending from the present to the penultimate glacial had such a chronology to our knowledge. Here, we present such a record from the annually laminated sediments of Lago Grande di Monticchio, southern Italy. Using this record we determine the duration (17.70 ± 0.20 ka) and age of onset (127.20 ± 1.60 ka B.P.) of the last interglacial, as reflected by terrestrial ecosystems. This record also reveals that the transitions at the beginning and end of the interglacial spanned only ≈100 and 150 years, respectively. Comparison with records of other earth-system components reveals complex leads and lags. During the penultimate deglaciation phase relationships are similar to those during the most recent deglaciation, peaks in Antarctic warming and atmospheric methane both leading Northern Hemisphere terrestrial warming. It is notable, however, that there is no evidence at Monticchio of a Younger Dryas-like oscillation during the penultimate deglaciation. Warming into the first major interstadial event after the last interglacial is characterized by markedly different phase relationships to those of the deglaciations, warming at Monticchio coinciding with Antarctic warming and leading the atmospheric methane increase. Diachroneity is seen at the end of the interglacial; several global proxies indicate progressive cooling after ≈115 ka B.P., whereas the main terrestrial response in the Mediterranean region is abrupt and occurs at 109.50 ± 1.40 ka B.P.” Achim Brauer, Judy R. M. Allen, Jens Mingram, Peter Dulski, Sabine Wulf, and Brian Huntley, PNAS January 9, 2007 vol. 104 no. 2 450-455, doi: 10.1073/pnas.0603321104. [Full text]

Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise – Overpeck et al. (2006) “Sea-level rise from melting of polar ice sheets is one of the largest potential threats of future climate change. Polar warming by the year 2100 may reach levels similar to those of 130,000 to 127,000 years ago that were associated with sea levels several meters above modern levels; both the Greenland Ice Sheet and portions of the Antarctic Ice Sheet may be vulnerable. The record of past ice-sheet melting indicates that the rate of future melting and related sea-level rise could be faster than widely thought.” Jonathan T. Overpeck, Bette L. Otto-Bliesner, Gifford H. Miller, Daniel R. Muhs, Richard B. Alley and Jeffrey T. Kiehl, Science 24 March 2006: Vol. 311 no. 5768 pp. 1747-1750, DOI: 10.1126/science.1115159. [FULL TEXT]

Simulating Arctic Climate Warmth and Icefield Retreat in the Last Interglaciation – Otto-Bliesner et al. (2006) “In the future, Arctic warming and the melting of polar glaciers will be considerable, but the magnitude of both is uncertain. We used a global climate model, a dynamic ice sheet model, and paleoclimatic data to evaluate Northern Hemisphere high-latitude warming and its impact on Arctic icefields during the Last Interglaciation. Our simulated climate matches paleoclimatic observations of past warming, and the combination of physically based climate and ice-sheet modeling with ice-core constraints indicate that the Greenland Ice Sheet and other circum-Arctic ice fields likely contributed 2.2 to 3.4 meters of sea-level rise during the Last Interglaciation.” Bette L. Otto-Bliesner, Shawn J. Marshall, Jonathan T. Overpeck, Gifford H. Miller, Aixue Hu and CAPE Last Interglacial Project members, Science 24 March 2006: Vol. 311 no. 5768 pp. 1751-1753, DOI: 10.1126/science.1120808. [FULL TEXT]

A model-data comparison of European temperatures in the Eemian interglacial – Kaspar et al. (2005) “We present a comparison of reconstructed and simulated January and July temperatures in Europe for a time slice (∼125 kyr BP) within the last interglacial (Eemian, ∼127–116 kyr BP). The reconstructions, based on pollen and plant macrofossils, were performed on 48 European sites using a method based on probability density functions (pdf-method). The reconstructed most probable climate values were compared with a global climate simulation which was realized with a coupled ocean-atmosphere general circulation model. Orbital parameters and greenhouse gas concentrations have been adapted to conditions at 125 kyr BP. Reconstructions and simulation are concordant in showing higher temperatures than today over most parts of Europe in summer and in revealing a west-east-gradient in winter temperature differences with increasing anomalies toward eastern Europe. The results indicate that differences in the orbital parameters are sufficient to explain the reconstructed Eemian temperature patterns.” Kaspar, F., N. Kühl, U. Cubasch, and T. Litt (2005), A model-data comparison of European temperatures in the Eemian interglacial, Geophys. Res. Lett., 32, L11703, doi:10.1029/2005GL022456. [Full text]

Increased seasonality in Middle East temperatures during the last interglacial period – Felis et al. (2004) “The last interglacial period (about 125,000 years ago) is thought to have been at least as warm as the present climate. Owing to changes in the Earth’s orbit around the Sun, it is thought that insolation in the Northern Hemisphere varied more strongly than today on seasonal timescales, which would have led to corresponding changes in the seasonal temperature cycle. Here we present seasonally resolved proxy records using corals from the northernmost Red Sea, which record climate during the last interglacial period, the late Holocene epoch and the present. We find an increased seasonality in the temperature recorded in the last interglacial coral. Today, climate in the northern Red Sea is sensitive to the North Atlantic Oscillation, a climate oscillation that strongly influences winter temperatures and precipitation in the North Atlantic region. From our coral records and simulations with a coupled atmosphere–ocean circulation model, we conclude that a tendency towards the high-index state of the North Atlantic Oscillation during the last interglacial period, which is consistent with European proxy records, contributed to the larger amplitude of the seasonal cycle in the Middle East.” Thomas Felis, Gerrit Lohmann, Henning Kuhnert, Stephan J. Lorenz, Denis Scholz, Jürgen Pätzold, Saber A. Al-Rousan & Salim M. Al-Moghrabi, Nature 429, 164-168 (13 May 2004) | doi:10.1038/nature02546. [Full text]

Timing, Duration, and Transitions of the Last Interglacial Asian Monsoon – Yuan et al. (2004) “Thorium-230 ages and oxygen isotope ratios of stalagmites from Dongge Cave, China, characterize the Asian Monsoon and low-latitude precipitation over the past 160,000 years. Numerous abrupt changes in 18O/16O values result from changes in tropical and subtropical precipitation driven by insolation and millennial-scale circulation shifts. The Last Interglacial Monsoon lasted 9.7 ± 1.1 thousand years, beginning with an abrupt (less than 200 years) drop in 18O/16O values 129.3 ± 0.9 thousand years ago and ending with an abrupt (less than 300 years) rise in 18O/16O values 119.6 ± 0.6 thousand years ago. The start coincides with insolation rise and measures of full interglacial conditions, indicating that insolation triggered the final rise to full interglacial conditions.” Daoxian Yuan, Hai Cheng, R. Lawrence Edwards, Carolyn A. Dykoski, Megan J. Kelly, Meiliang Zhang, Jiaming Qing, Yushi Lin, Yongjin Wang, Jiangyin Wu, Jeffery A. Dorale, Zhisheng An and Yanjun Cai, Science 23 April 2004: Vol. 304 no. 5670 pp. 575-578, DOI: 10.1126/science.1091220. [Full text]

Continental European Eemian and early Würmian climate evolution: comparing signals using different quantitative reconstruction approaches based on pollen – Klotz et al. (2003) “Analyses of Eemian climate dynamics based on different reconstruction methods were conducted for several pollen sequences in the northern alpine foreland. The modern analogue and mutual climate sphere techniques used, which are briefly presented, complement one another with respect to comparable results. The reconstructions reveal the occurrence of at least two similar thermal periods, representing temperate oceanic conditions warmer and with a higher humidity than today. Intense changes of climate processes become obvious with a shift of winter temperatures of about 15 °C from the late Rissian to the first thermal optimum of the Eemian. The transition shows a pattern of summer temperatures and precipitation increasing more rapidly than winter temperatures. With the first optimum during the Pinus–Quercetum mixtum–Corylus phase (PQC) at an early stage of the Eemian and a second optimum period at a later stage, which is characterised by widespread Carpinus, climate gradients across the study area were less intense than today. Average winter temperatures vary between −1.9 and 0.4 °C (present-day −3.6 to 1.4 °C), summer temperatures between 17.8 and 19.6 °C (present-day 14 to 18.9 °C). The timberline expanded about 350 m when compared to the present-day limit represented by Pinus mugo. Whereas the maximum of temperature parameters is related to the first optimum, precipitation above 1100 mm is higher during the second warm period concomitant to somewhat reduced temperatures. Intermediate, smaller climate oscillations and a cooling becomes obvious, which admittedly represent moderate deterioration but not extreme chills. During the boreal semicontinental Eemian Pinus–Picea–Abies phase, another less distinct fluctuation occurs, initiating the oscillating shift from temperate to cold conditions.” Stefan Klotz, Joel Guiot, Volker Mosbrugger, Global and Planetary Change, Volume 36, Issue 4, May 2003, Pages 277–294,

Last Interglacial Climates – Kukla et al. (2002) “The last interglacial, commonly understood as an interval with climate as warm or warmer than today, is represented by marine isotope stage (MIS) 5e, which is a proxy record of low global ice volume and high sea level. It is arbitrarily dated to begin at approximately 130,000 yr B.P. and end at 116,000 yr B.P. with the onset of the early glacial unit MIS 5d. The age of the stage is determined by correlation to uranium–thorium dates of raised coral reefs. The most detailed proxy record of interglacial climate is found in the Vostok ice core where the temperature reached current levels 132,000 yr ago and continued rising for another two millennia. Approximately 127,000 yr ago the Eemian mixed forests were established in Europe. They developed through a characteristic succession of tree species, probably surviving well into the early glacial stage in southern parts of Europe. After ca. 115,000 yr ago, open vegetation replaced forests in northwestern Europe and the proportion of conifers increased significantly farther south. Air temperature at Vostok dropped sharply. Pulses of cold water affected the northern North Atlantic already in late MIS 5e, but the central North Atlantic remained warm throughout most of MIS 5d. Model results show that the sea surface in the eastern tropical Pacific warmed when the ice grew and sea level dropped. The essentially interglacial conditions in southwestern Europe remained unaffected by ice buildup until late MIS 5d when the forests disappeared abruptly and cold water invaded the central North Atlantic ca. 107,000 yr ago.” George J. Kukla, Michael L. Bender, Jacques-Louis de Beaulieu, Gerard Bond, Wallace S. Broecker, Piet Cleveringa, Joyce E. Gavin, Timothy D. Herbert, John Imbrie, Jean Jouzel, Lloyd D. Keigwin, Karen-Luise Knudsen, Jerry F. McManus, Josef Merkt, Daniel R. Muhs, Helmut Müller, Richard Z. Poore, Stephen C. Porter, Guy Seret, Nicholas J. Shackleton, Charles Turner, Polychronis C. Tzedakis, Isaac J. Winograd, Quaternary Research, Volume 58, Issue 1, July 2002, Pages 2–13, [Full text]

High-resolution record of climate stability in France during the last interglacial period – Rioual et al. (2001) “The last interglacial period (127–110 kyr ago) has been considered to be an analogue to the present interglacial period, the Holocene, which may help us to understand present climate evolution. But whereas Holocene climate has been essentially stable in Europe, variability in climate during the last interglacial period has remained unresolved, because climate reconstructions from ice cores, continental records and marine sediment cores give conflicting results for this period. Here we present a high-resolution multi-proxy lacustrine record of climate change during the last interglacial period, based on oxygen isotopes in diatom silica, diatom assemblages and pollen–climate transfer functions from the Ribains maar in France. Contrary to a previous study, our data do not show a cold event interrupting the warm interglacial climate. Instead, we find an early temperature maximum with a transition to a colder climate about halfway through the sequence. The end of the interglacial period is clearly marked by an abrupt change in all proxy records. Our study confirms that in southwestern Europe the last interglacial period was a time of climatic stability and is therefore still likely to represent a useful analogue for the present climate.” Patrick Rioual, Valérie Andrieu-Ponel, Miri Rietti-Shati, Richard W. Battarbee, Jacques-Louis de Beaulieu, Rachid Cheddadi, Maurice Reille, Helena Svobodova & Aldo Shemesh, Nature 413, 293-296 (20 September 2001) | doi:10.1038/35095037.

Comparison of the last interglacial climate simulated by a coupled global model of intermediate complexity and an AOGCM – Kubatzki et al. (2000) “The climate at the Last Interglacial Maximum (125 000 years before present) is investigated with the atmosphere-ocean general circulation model ECHAM-1/LSG and with the climate system model of intermediate complexity CLIMBER-2. Comparison of the results of the two models reveals broad agreement in most large-scale features, but also some discrepancies. The fast turnaround time of CLIMBER-2 permits one to perform a number of sensitivity experiments to (1) investigate the possible reasons for these differences, in particular the impact of different freshwater fluxes to the ocean, (2) analyze the sensitivity of the results to changes in the definition of the modern reference run concerning CO2 levels (preindustrial versus “present”), and (3) estimate the role of vegetation in the changed climate. Interactive vegetation turns out to be capable of modifying the initial climate signals significantly, leading especially to warmer winters in large parts of the Northern Hemisphere, as indicated by various paleodata. Differences due to changes in the atmospheric CO2 content and due to interactive vegetation are shown to be at least of the same order of magnitude as differences between the two completely different models, demonstrating the importance of careful experimental design.” C. Kubatzki, M. Montoya, S. Rahmstorf, A. Ganopolski and M. Claussen, Climate Dynamics, Volume 16, Numbers 10-11 (2000), 799-814, DOI: 10.1007/s003820000078. [Full text]

Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet – Cuffey & Marshall (2000) “During the last interglacial period (the Eemian), global sea level was at least three metres, and probably more than five metres, higher than at present. Complete melting of either the West Antarctic ice sheet or the Greenland ice sheet would today raise sea levels by 6–7 metres. But the high sea levels during the last interglacial period have been proposed to result mainly from disintegration of the West Antarctic ice sheet, with model studies attributing only 1–2 m of sea-level rise to meltwater from Greenland. This result was considered consistent with ice core evidence4, although earlier work had suggested a much reduced Greenland ice sheet during the last interglacial period6. Here we reconsider the Eemian evolution of the Greenland ice sheet by combining numerical modelling with insights obtained from recent central Greenland ice-core analyses. Our results suggest that the Greenland ice sheet was considerably smaller and steeper during the Eemian, and plausibly contributed 4–5.5 m to the sea-level highstand during that period. We conclude that the high sea level during the last interglacial period most probably included a large contribution from Greenland meltwater and therefore should not be interpreted as evidence for a significant reduction of the West Antarctic ice sheet.” Kurt M. Cuffey & Shawn J. Marshall, Nature 404, 591-594 (6 April 2000) | doi:10.1038/35007053. [Full text]

Multiproxy climate reconstructions for the Eemian and Early Weichselian – Aalbersberg & Litt (1998) “Palaeobotanical, coleopteran and periglacial data from 106 sites across northwestern Europe have been analysed in order to reconstruct palaeoclimatic conditions during the Eemian and Early Weichselian. Three time slices in the Eemian and four in the Early Weichselian have been considered. In the Pinus–Quercetum mixtum–Corylus phase of the Eemian, summer temperatures were probably at their highest and the botanic evidence suggests a southeast to northwest gradient for both the warmest and coldest month. Coleoptera indicate that the summers in southern England were several degrees warmer than those of present day. The climate during theCarpinus–Picea phase was uniform and oceanic without obvious gradients. In the final time slice of the Eemian, the Pinus–Picea–Abies phase, temperatures of the warmest month seem to drop slightly with some indication of a shift towards a more boreal and suboceanic climate. The reconstruction of the palaeoclimate in the Herning Stadial and Rederstall Stadial is hampered by the limited number of sites, but botanical evidence suggests a gradient in temperature of the coldest month from east to west. Coleoptera from the Herning Stadial in central England and eastern Germany suggest similarly cold and continental climates. During the Brørup Interstadial and the Odderade Interstadial the botanical evidence suggests that the minimum mean July temperatures rose to 15–16°C but during the coldest month these temperatures show a gradient between −13°C in the east and −5°C in the west.” Gerard Aalbersberg, Thomas Litt, Journal of Quaternary Science, Special Issue: Palaeoclimate of the last Interglacial- Glacial Cycle in Western and Central Europe, Volume 13, Issue 5, pages 367–390, September/October 1998, DOI: 10.1002/(SICI)1099-1417(1998090)13:53.0.CO;2-I..

An analysis of Eemian climate in Western and Central Europe – Zagwijn (1996) “On the basis of 31 pollen diagrams and additional data for botanical macrofossils an analysis is made of the Last Interglacial (Eemian) climatic history in Western and Central Europe. The main tool for this analysis is the climatic indicator species method. Only selected woody species are used for the quantification of data. Partial climatic range diagrams are presented for: Abies alba, Acer monspessulanum, Acer tataricum, Buxus sempervirens, Tilia tomentosa. The problem of time correlation and pollen zonation of the Eemian is discussed. The climatic analysis itself is based on an improved version of the indicator species method. In this version not every site is analysed for its climatic values. Instead maps and tables on the migrational history of Hedera, Ilex, Buxus, Abies and species of Acer, Tilia and Abies are the basis for climatic maps showing respectively January and July isotherms for the periods of the Corylus zone (E4a) and the Carpinus zone (E5). It is concluded that mean January temperatures were as much as 3°C higher at Amsterdam (The Netherlands), than at present, and mean temperatures in July were 2°C higher. However, the thermal maximum in winter was later (zone E5) than the summer thermal maximum (zone E4a). Winter temperatures changed parallel to rise and fall of global sea-level. Precipitation changes are more difficult to estimate. In the first part of the Eemian precipitation must have been relatively low, but from zone E4b onward it increased to higher values, reaching 800 mm and probably substantially more in zones E5 and E6. Hence the Eemian climate was in its beginning relatively more contintental, and later (from E4b onward) more oceanic. However, as compared with the Holocene, the Eemian climate was, generally speaking, more oceanic.” W.H. Zagwijn, Quaternary Science Reviews, Volume 15, Issues 5–6, 1996, Pages 451–469,

Rapid changes in ocean circulation and heat flux in the Nordic seas during the last interglacial period – Fronval & Jansen (1996) “THE apparent similarity of climate variability in the North Atlantic region in the last interglacial period and the present interglacial (Holocene) has recently been challenged by the rapid oscillations in climate conditions indicated by some marine and terrestrial climate records8–10 for the last interglacial. Ocean circulation in the northern North Atlantic seems to be intimately coupled to the processes of climate change on various time-scales, so that climate variability—and the associated mechanisms of change—should be well recorded by sediments from these high latitudes. Previous studies in this region have indeed indicated an apparently less stable last-interglacial climate than at middle latitudes of the North Atlantic Ocean4. Here we present detailed records from marine sediments in the Nordic seas of oceanographic conditions during the last interglacial. The records show three large sea surface temperature fluctuations, a weakening of the east–west sea surface temperature gradient with time, and changes in deep-water properties. In contrast, similar analyses of a core from the same region indicate that sea surface temperature during the Holocene has been relatively stable. Our data—along with those from the Labrador Sea7—indicate rapid changes in ocean circulation and oceanic heat fluxes at high northern latitudes during the last interglacial, which may have been associated with marked temperature changes on adjacent continents.” Torben Fronval & Eystein Jansen, Nature 383, 806 – 810 (31 October 1996); doi:10.1038/383806a0.

The Last Interglaciation in Arctic and Subarctic Regions: Time Frame, Structure, and Duration: Selected Papers from a LIGA Symposium Held in Saint-Michel des Saints, Quebec, Canada, May 4-7, 1993 – Lauritzen & Anderson (1995) Selected papers in question are included to this issue of journal Quaternary Research (including Brigham-Grette & Hopkins paper presented below). Stein-Erik Lauritzen, Patricia M. Anderson, Quaternary Research, Volume 43, Issue 2, March 1995, Pages 115–116.

Emergent Marine Record and Paleoclimate of the Last Interglaciation along the Northwest Alaskan Coast – Brigham-Grette & Hopkins (1995) “The last interglacial high sea-level stand, the Pelukian transgression of isotope substage 5e, is recorded along the western and northern coasts of Alaska by discontinuous but clearly traceable marine terraces and coastal landforms up to about 10 m altitude. The stratigraphy indicates that sea level reached this altitude only once during the last interglacial cycle. From the type area at Nome, to St. Lawrence Island in the Bering Sea, to the eastern limit of the Beaufort Sea, Pelukian deposits contain extralimital faunas indicating that coastal waters were warmer than present. Amino acid ratios in molluscs from these deposits decrease to the north toward Barrow, consistent with the modern regional temperature gradient. Fossil assemblages at Nome and St. Lawrence Island suggest that the winter sea-ice limit was north of Bering Strait, at least 800 km north of its present position, and the Bering Sea was perennially ice-free. Microfauna in Pelukian sediments recovered from boreholes indicate that Atlantic water may have been present on the shallow Beaufort Shelf, suggesting that the Arctic Ocean was not stratified and the Arctic sea-ice cover was not perennial for some period. In coastal regions of western Alaska, spruce woodlands extended westward beyond their modern range and in northern Alaska, on the Arctic Coastal Plain, spruce groves may have entered the upper Colville River basin. The Flaxman Member of the Gubik Formation on the Alaskan Arctic Coastal Plain was deposited during marine isotope substage 5a and records the breakup of an intra-stage 5 ice sheet over northwestern Keewatin.” Julie Brigham-Grette, David M. Hopkins, Quaternary Research, Volume 43, Issue 2, March 1995, Pages 159–173, [FULL TEXT]

High-resolution climate records from the North Atlantic during the last interglacial – McManus et al. (1994) “THE two deep ice cores recovered by the GRIP and GISP2 projects at Summit, Greenland, agree in detail over the past 100,000 years and demonstrate dramatic climate variability in the North Atlantic region during the last glacial, before the current period of Holocene stability. This glacial climate instability has subsequently been documented in the marine sedimentary record of surface-ocean conditions in the North Atlantic. Before 100 kyr ago the two ice core records are discrepant, however, casting doubt on whether the oxygen isotope fluctuations during the last interglacial (Eemian) seen in the GRIP core represent a true climate signal. Here we present high-resolution records of foraminiferal assemblages and ice-rafted detritus from two North Atlantic cores for the interval 65 kyr to 135 kyr ago, extending the surface-ocean record back to the Eemian. The correlation between our records and the Greenland ice-core records is good throughout the period in which the two ice cores agree, suggesting a regionally coherent climate response. During the Eemian, our marine records show a more stable climate than that implied by the GRIP ice core, suggesting that localized phenomena may be responsible for the variability in the latter record during the Eemian.” J. F. McManus, G. C. Bond, W. S. Broecker, S. Johnsen, L. Labeyrie & S. Higgins, Nature 371, 326 – 329 (22 September 1994); doi:10.1038/371326a0. [Full text]

Constraints on the age and duration of the last interglacial period and on sea-level variations – Lambeck & Nakada (1992) “The relation between height and age of shorelines formed during the last interglacial period, as revealed by coral reefs, cannot be related directly to changes in ocean volume because of the effect of isostatic uplift in response to changes in ice-sheet loading. Sea-level changes at sites near the melting ice sheet, such as Bermuda and the Caribbean islands, differ from those along the Australian margin. Modelling of these differences constrains the times of onset and termination of the last interglacial, which are at variance with those deduced from oxygen-isotope studies of deep-sea cores.” Kurt Lambeck & Masao Nakada, Nature 357, 125 – 128 (14 May 1992); doi:10.1038/357125a0.

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Papers on global warming detection from global temperature series

Posted by Ari Jokimäki on May 25, 2012

This is a list of papers on global warming detection from global temperature series (i.e. papers that estimate if global warming signal can be statistically significantly distinguished from random noise). The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

UPDATE (July 24, 2013): Foster & Rahmstorf (2011) added.

A Bayesian approach to detecting change points in climatic records – Ruggieri (2012) “Given distinct climatic periods in the various facets of the Earth’s climate system, many attempts have been made to determine the exact timing of ‘change points’ or regime boundaries. However, identification of change points is not always a simple task. A time series containing N data points has approximately Nk distinct placements of k change points, rendering brute force enumeration futile as the length of the time series increases. Moreover, how certain are we that any one placement of change points is superior to the rest? This paper introduces a Bayesian Change Point algorithm which provides uncertainty estimates both in the number and location of change points through an efficient probabilistic solution to the multiple change point problem. To illustrate its versatility, the Bayesian Change Point algorithm is used to analyse both the NOAA/NCDC annual global surface temperature anomalies time series and the much longer δ18O record of the Plio-Pleistocene.” Eric Ruggieri, International Journal of Climatology, DOI: 10.1002/joc.3447.

Global temperature evolution 1979–2010 – Foster & Rahmstorf (2011) “We analyze five prominent time series of global temperature (over land and ocean) for their common time interval since 1979: three surface temperature records (from NASA/GISS, NOAA/NCDC and HadCRU) and two lower-troposphere (LT) temperature records based on satellite microwave sensors (from RSS and UAH). All five series show consistent global warming trends ranging from 0.014 to 0.018 K yr−1. When the data are adjusted to remove the estimated impact of known factors on short-term temperature variations (El Niño/southern oscillation, volcanic aerosols and solar variability), the global warming signal becomes even more evident as noise is reduced. Lower-troposphere temperature responds more strongly to El Niño/southern oscillation and to volcanic forcing than surface temperature data. The adjusted data show warming at very similar rates to the unadjusted data, with smaller probable errors, and the warming rate is steady over the whole time interval. In all adjusted series, the two hottest years are 2009 and 2010.” Grant Foster and Stefan Rahmstorf 2011 Environ. Res. Lett. 6 044022 doi:10.1088/1748-9326/6/4/044022. [Full text]

Detecting abrupt climate changes on different time scales – Matyasovszky (2011) “Two concepts are introduced for detecting abrupt climate changes. In the first case, the sampling frequency of climate data is high as compared to the frequency of climate events examined. The method is based on a separation of trend and noise in the data and is applicable to any dataset that satisfies some mild smoothness and statistical dependence conditions for the trend and the noise, respectively. We say that an abrupt change occurs when the first derivative of the trend function has a discontinuity and the task is to identify such points. The technique is applied to Northern Hemisphere temperature data from 1850 to 2009, Northern Hemisphere temperature data from proxy data, a.d. 200–1995 and Holocene δ18O values going back to 11,700 years BP. Several abrupt changes are detected that are, among other things, beneficial for determining the Medieval Warm Period, Little Ice Age and Holocene Climate Optimum. In the second case, the sampling frequency is low relative to the frequency of climate events studied. A typical example includes Dansgaard–Oeschger events. The methodology used here is based on a refinement of autoregressive conditional heteroscedastic models. The key element of this approach is the volatility that characterises the time-varying variance, and abrupt changes are defined by high volatilities. The technique applied to δ18O values going back to 122,950 years BP is suitable for identifying DO events. These two approaches for the two cases are closely related despite the fact that at first glance, they seem quite different.” István Matyasovszky, Theoretical and Applied Climatology, Volume 105, Numbers 3-4 (2011), 445-454, DOI: 10.1007/s00704-011-0401-4.

Testing for Deterministic Trends in Global Sea Surface Temperature – Barbosa (2011) “Long-term variability in global sea surface temperature (SST) is often quantified by the slope from a linear regression fit. Attention is then focused on assessing the statistical significance of the derived slope parameter, but the adequacy of the linear model itself, and the inherent assumption of a deterministic linear trend, is seldom tested. Here, a parametric statistical test is applied to test the hypothesis of a linear deterministic trend in global sea surface temperature. The results show that a linear slope is not adequate for describing the long-term variability of sea surface temperature over most of the earth’s surface. This does not mean that sea surface temperature is not increasing, rather that the increase should not be characterized by the slope from a linear fit. Therefore, describing the long-term variability of sea surface temperature by implicitly assuming a deterministic linear trend can give misleading results, particularly in terms of uncertainty, since the actual increase could be considerably larger than the one predicted by a deterministic linear model.” Barbosa, Susana M., 2011: Testing for Deterministic Trends in Global Sea Surface Temperature. J. Climate, 24, 2516–2522. doi:

1963: The break point of the Northern Hemisphere temperature trend during the twentieth century – Ivanov & Evtimov (2010) “Besides gradually, climate can also change abruptly. The global surface temperature series is a major indicator of such changes. Using rigorous statistical tools, we show that during the twentieth century the time series of annual Northern Hemisphere surface temperature is well described by a trend-stationary process, but the trend line breaks in 1963. After six transitory years, in 1970, the temperature course locks up into a new regime with a triple linear warming rate. For the emergence and abruptness of the break we reveal the key roles of the Mount Agung eruption and the interannual to interdecadal changes of the major modes and patterns of climate variability. We offer an abrupt climate shift scenario based on the adaptivity of climatic regimes against instant external forcings.” Martin A. Ivanov, Stilian N. Evtimov, International Journal of Climatology, Volume 30, Issue 11, pages 1738–1746, September 2010, DOI: 10.1002/joc.2002.

Warming Break Trends and Fractional Integration in the Northern, Southern, and Global Temperature Anomaly Series – Gil-Alana (2008) “This paper deals with the estimation of time trends in temperature anomaly series. However, instead of imposing that the estimated residuals from the time trends are covariance stationary processes with spectral density that is positive and finite at the zero frequency [I(0)], the author allows them to be fractionally integrated. In this context, a new procedure for testing fractional integration with segmented trends is applied to the northern, southern, and global temperature anomaly series. The results show that the three series are fractionally integrated, and the warming effects are substantially higher after the break in all cases.” Gil-Alana, Luis A., 2008: Warming Break Trends and Fractional Integration in the Northern, Southern, and Global Temperature Anomaly Series. J. Atmos. Oceanic Technol., 25, 570–578. doi: [Full text]

Semiparametric estimation and testing of the trend of temperature series – Gao & Hawthorne (2006) “The application of a partially linear model to global and hemispheric temperature series is proposed. Partially linear modelling allows the trend to take a very general form rather than imposing the restriction of linearity seen in existing studies. The removal of the linearity restriction is based on the fact that it is well accepted that a significant trend is present in global temperature series. The model will allow for the data to ‘speak for themselves’ with regard to the form of the trend. The results initially reveal that a linear trend does not approximate well the behaviour of global or hemispheric temperature series. This is further confirmed through a formal testing procedure. The results suggest that little faith should be instilled in long-term forecasts of temperatures in which the trend of global and hemispheric series is assumed to be linear. All the current evidence suggest that temperatures will continue to rise in an unknown and probably nonlinear fashion.” Jiti Gao, Kim Hawthorne, The Econometrics Journal, Volume 9, Issue 2, pages 332–355, July 2006, DOI: 10.1111/j.1368-423X.2006.00188.x.

Are winters getting warmer? – Vogelsang & Franses (2006) “We examine whether any trends in monthly temperatures are the same through-out the year for various lengthy series. The data concern the world, the northern and southern hemispheres, and about three centuries of data for the United Kingdom and the Netherlands. For the empirical exercise, we rely on new and accurate tests which have been recently developed. These tests do not have standard distributions, so that critical values have to be tabulated. The empirical findings include significant worldwide temperature increases, differences across months for the northern hemisphere, and warming winters for the UK and the Netherlands.” Timothy J. Vogelsang, Philip Hans Franses, Environmental Modelling & Software, Volume 20, Issue 11, November 2005, Pages 1449–1455,

Tests of common deterministic trend slopes applied to quarterly global temperature data – Fomby & Vogelsang (2003) “We examine the global warming temperature data sets of Jones et al. (1999) and Vinnikov et al. (1994) in the context of the multivariate deterministic trend-testing framework of Franses and Vogelsang (2002). We find that, across all seasons, global warming seems to be present for the globe and for the northern and southern hemispheres. Globally and within hemispheres, it appears that seasons are not warming equally fast. In particular, winters appear to be warming faster than summers. Across hemispheres, it appears that the winters in the northern and southern hemispheres are warming equally fast whereas the remaining seasons appear to have unequal warming rates. The results obtained here seem to coincide with the findings of Kaufmann and Stern (2002) who use cointegration analysis and find that the hemispheres are warming at different rates.” Thomas B. Fomby, Timothy J. Vogelsang, (2003) “TESTS OF COMMON DETERMINISTIC TREND SLOPES APPLIED TO QUARTERLY GLOBAL TEMPERATURE DATA”, , Vol. Iss: 17, pp.29 – 43, doi: 10.1016/S0731-9053(03)17002-8.

The Application of Size-Robust Trend Statistics to Global-Warming Temperature Series – Fomby & Vogelsang (2002) “In this note, new evidence is provided confirming that global temperature series spanning back to the mid-1800s have statistically significant positive trends. Although there is a growing consensus that global temperatures are on the rise systematically, some recent studies have pointed out that strong serial correlation (or a unit root) in global temperature data could, in theory, generate spurious evidence of a significant positive trend. In other words, strong serially correlated data can mimic trending behavior over fixed periods of time. A serial-correlation–robust trend test recently was proposed that controls for the possibility of spurious evidence due to strong serial correlation. This new test is valid whether the errors are stationary or have a unit root (strong serial correlation). This test also has the attractive feature that it does not require estimates of serial correlation nuisance parameters. The test is applied to six annual global temperature series, and it provides strong evidence that global temperature series have positive trends that are statistically significant even when controlling for the possibility of strong serial correlation. The point estimates of the rate of increase in the trend suggest that temperatures have risen about 0.5°C (1.0°F) 100 yr−1. If the analysis is restricted to twentieth-century data, many of the point estimates are closer to 0.6°C.” Fomby, Thomas B., Timothy J. Vogelsang, 2002: The Application of Size-Robust Trend Statistics to Global-Warming Temperature Series. J. Climate, 15, 117–123, doi:;2. [Full text]

Structural Time Series Models and Trend Detection in Global and Regional Temperature Series – Zheng & Basher (1999) “A unified statistical approach to identify suitable structural time series models for annual mean temperature is proposed. This includes a generalized model that can represent all the commonly used structural time series models for trend detection, the use of differenced series (successive year-to-year differences), and explicit methods for comparing the validity of no-trend nonstationary residuals models relative to trend models. Its application to Intergovernmental Panel on Climate Change global and latitude-belt temperature series reveals that a linear trend model (starting in 1890, with Southern Oscillation index signal removal and a red noise residuals process) is the optimal model for much of the globe, from the Northern Hemisphere Tropics to the Southern Hemisphere midlatitudes, but that a random stationary increment process (with no deterministic trend) is preferred for the northern part of the Northern Hemisphere. The result for the higher northern latitudes appears to be related to the greater climate variability there and does not exclude the possibility of a trend being present. The hemispheric and global series will contain a mixture of the two processes but are dominated by and best represented by the linear trend model. The latitudinal detectability of trends is oppositely matched to where GCMs indicate greatest anthropogenic trend, that is, it is best for the Tropics rather than for the high latitudes. The results reinforce the view that the global temperatures are affected by a long-term trend that is not of natural origin.” Zheng, Xiaogu, Reid E. Basher, 1999: Structural Time Series Models and Trend Detection in Global and Regional Temperature Series. J. Climate, 12, 2347–2358, doi:;2. [Full text]

Trend Estimation and Regression Analysis in Climatological Time Series: An Application of Structural Time Series Models and the Kalman Filter – Visser & Molenaar (1995) “The detection of trends in climatological data has become central to the discussion on climate change due to the enhanced greenhouse effect. To prove detection, a method is needed (i) to make inferences on significant rises or declines in trends, (ii) to take into account natural variability in climate series, and (iii) to compare output from GCMs with the trends in observed climate data. To meet these requirements, flexible mathematical tools are needed. A structural time series model is proposed with which a stochastic trend, a deterministic trend, and regression coefficients can be estimated simultaneously. The stochastic trend component is described using the class of ARIMA models. The regression component is assumed to be linear. However, the regression coefficients corresponding with the explanatory variables may be time dependent to validate this assumption. The mathematical technique used to estimate this trend-regression model is the Kaiman filter. The main features of the filter are discussed. Examples of trend estimation are given using annual mean temperatures at a single station in the Netherlands (1706–1990) and annual mean temperatures at Northern Hemisphere land stations (1851–1990). The inclusion of explanatory variables is shown by regressing the latter temperature series on four variables: Southern Oscillation index (SOI), volcanic dust index (VDI), sunspot numbers (SSN), and a simulated temperature signal, induced by increasing greenhouse gases (GHG). In all analyses, the influence of SSN on global temperatures is found to be negligible. The correlations between temperatures and SOI and VDI appear to be negative. For SOI, this correlation is significant, but for VDI it is not, probably because of a lack of volcanic eruptions during the sample period. The relation between temperatures and GHG is positive, which is in agreement with the hypothesis of a warming climate because of increasing levels of greenhouse gases. The prediction performance of the model is rather poor, and possible explanations are discussed.” Visser, H., J. Molenaar, 1995: Trend Estimation and Regression Analysis in Climatological Time Series: An Application of Structural Time Series Models and the Kalman Filter. J. Climate, 8, 969–979, doi:;2. [Full text]

Selecting a Model for Detecting the Presence of a Trend – Woodward & Gray (1995) “The authors consider the problem of determining whether the upward trending behavior in the global temperature anomaly series should be forecast to continue. To address this question, the generic problem of determining whether an observed trend in a time series realization is a random (i.e., short-term) trend or a deterministic (i.e., permanent) trend is considered. The importance of making this determination is that forecasts based on these two scenarios are dramatically different. Forecasts based on a series with random trends will not predict the observed trend to continue, while forecasts based on a model with deterministic trend will forecast the trend to continue into the future. In this paper, the authors consider an autoregressive integrated moving average (ARIMA) model and a “deterministic forcing function + autoregressive (AR) noise” model as possible random trend and deterministic trend models, respectively, for realizations displaying trending behavior. A bootstrap-based classification procedure for classifying an observed time series realization as ARIMA or “function + AR” using linear and quadratic forcing functions is introduced. A simulation study demonstrates that the procedure is useful in distinguishing between realizations from these two models. A unit-root test is also examined in an effort to distinguish between these two types of models. Using the techniques developed here, the temperature anomaly series are classified as ARIMA (i.e., having random trends).” Woodward, Wayne A., H. L. Gray, 1995: Selecting a Model for Detecting the Presence of a Trend. J. Climate, 8, 1929–1937, doi:;2. [Full text]

Global Warming and the Problem of Testing for Trend in Time Series Data – Woodward & Gray (1993)“In recent years a number of statistical tests have been proposed for testing the hypothesis that global warming is occurring. The standard approach is to examine one or two of the more prominent global temperature datasets by letting Yt = a + bt + Et, where Yt represents the temperature at time t and Et represents error from the trend line, and to test the hypothesis that b = 0. Several authors have applied these tests for trend to determine whether or not a significant long-term or deterministic trend exists, and have generally concluded that there is a significant deterministic trend in the data. However, we show that certain autoregressive-moving average (ARMA) models may also be very reasonable models for these data due to the random trends present in their realizations. In this paper, we provide simulation evidence to show that the tests for trend detect a deterministic trend in a relatively high percentage of realizations from a wide range of ARMA models, including those obtained for the temperature series, for which it is improper to forecast a trend to continue over more than a very short time period. Thus, we demonstrate that trend tests based on models such as Yt = a + bt + Et, where Yt for the purpose of prediction or inference concerning future behavior should be used with caution. Of course, the projections that the warming trend will extend into the future are largely based on such factors as the buildup of atmospheric greenhouse gases. We have shown here, however, that based solely on the available temperature anomaly series, it is difficult to conclude that the trend will continue over any extended length of time.” Woodward, Wayne A., H. L. Gray, 1993: Global Warming and the Problem of Testing for Trend in Time Series Data. J. Climate, 6, 953–962, doi:;2. [Full text]

Climate spectra and detecting climate change – Bloomfield & Nychka (1992) “Part of the debate over possible climate changes centers on the possibility that the changes observed over the previous century are natural in origin. This raises the question of how large a change could be expected as a result of natural variability. If the climate measurement of interest is modelled as a stationary (or related) Gaussian time series, this question can be answered in terms of (a) the way in which change is estimated, and (b) the spectrum of the time series. These computations are illustrated for 128 years of global temperature data using some simple measures of change and for a variety of possible temperature spectra. The results highlight the time scales on which it is important to know the magnitude of natural variability. The uncertainties in estimates of trend are most sensitive to fluctuations in the temperature series with periods from approximately 50 to 500 years. For some of the temperature spectra, it was found that the standard error of the least squares trend estimate was 3 times the standard error derived under the naïve assumption that the temperature series was uncorrelated. The observed trend differs from zero by more than 3 times the largest of the calculated standard errors, however, and is therefore highly significant.” Peter Bloomfield and Douglas Nychka, Climatic Change, Volume 21, Number 3 (1992), 275-287, DOI: 10.1007/BF00139727.

Trends in global temperature – Bloomfield (1992) “Statistical models consisting of a trend plus serially correlated noise may be fitted to observed climate data such as global surface temperature, the trend and noise representing systematic change and other variations, respectively. When such a model is fitted, the estimated character of the noise determines the precision of the estimated trend, and hence the precision of the estimate of the magnitude of the systematic change in the variable considered. The results of fitting such models to global temperature imply that there is uncertainty in the amount of temperature change over the past century of up to ± 0.2 °C, but that the change of around one half of a degree Celsius is significantly different from zero. The statistical models for climate variability also imply that the observed temperature data provide only imprecise information about the climate sensitivity. This is defined here as the equilibrium response of global temperature to a doubling of the atmospheric concentration of carbon dioxide. The temperature changes observed to date are compatible with a wide range of climate sensitivities, from 0.7 °C to 2.2 °C. When data uncertainties are taken into account, the interval widens even further.” Peter Bloomfield, Climatic Change, Volume 21, Number 1 (1992), 1-16, DOI: 10.1007/BF00143250.

Inference about trends in global temperature data – Galbraith & Green (1992) “Interpretation of the effects of increasing atmospheric carbon dioxide on temperature is made more difficult by the fact that it is unclear whether sufficient global warming has taken place to allow a statistically significant finding of any upward trend in the temperature series. We add to the few existing statistical results by reporting tests for both deterministic and stochastic non-stationarity (trends) in time series of global average temperature. We conclude that the statistical evidence is sufficient to reject the hypothesis of a stochastic trend; however, there is evidence of a trend which could be approximated by a deterministic linear model.” John W. Galbraith and Christopher Green, Climatic Change, Volume 22, Number 3 (1992), 209-221, DOI: 10.1007/BF00143028.

Interdecadal oscillations and the warming trend in global temperature time series – Ghil & Vautard (1991) “THE ability to distinguish a warming trend from natural variability is critical for an understanding of the climatic response to increasing greenhouse-gas concentrations. Here we use singular spectrum analysis1 to analyse the time series of global surface air tem-peratures for the past 135 years, allowing a secular warming trend and a small number of oscillatory modes to be separated from the noise. The trend is flat until 1910, with an increase of 0.4 °C since then. The oscillations exhibit interdecadal periods of 21 and 16 years, and interannual periods of 6 and 5 years. The interannual oscillations are probably related to global aspects of the El Niño-Southern Oscillation (ENSO) phenomenon. The interdecadal oscillations could be associated with changes in the extratropical ocean circulation. The oscillatory components have combined (peak-to-peak) amplitudes of >0.2 °C, and therefore limit our ability to predict whether the inferred secular warming trend of 0.005 °Cyr−1 will continue. This could postpone incontrovertible detection of the greenhouse warming signal for one or two decades.” M. Ghil & R. Vautard, Nature 350, 324 – 327 (28 March 1991); doi:10.1038/350324a0. [Full text]

Global Warming as a Manifestation of a Random Walk – Gordon (1991) “Global and hemispheric series of surface temperature anomalies are examined in an attempt to isolate any specific features of the structure of the series that might contribute to the global warming of about 0.5°C which has been observed over the past 100 years. It is found that there are no significant differences between the means of the positive and negative values of the changes in temperature from one year to the next; neither do the relative frequencies of the positive and negative values differ from the frequencies that would be expected by chance with a probability near 0.5. If the interannual changes are regarded as changes of unit magnitude and plotted in a Cartesian frame of reference with time measured along the x axis and yearly temperature differences along the y axis, the resulting path closely resembles the kind of random walk that occurs during a coin-tossing game. We hypothesize that the global and hemispheric temperature series are the result of a Markov process. The climate system is subjected to various forms of random impulses. It is argued that the system fails to return to its former state after reacting to an impulse but tends to adjust to a new state of equilibrium as prescribed by the shock. This happens because a net positive feedback accompanies each shock and slightly alters the environmental state.” Gordon, A. H., 1991: Global Warming as a Manifestation of a Random Walk. J. Climate, 4, 589–597, doi:;2. [Full text]

Detecting CO2-induced climatic change – Wigley & Jones (1981) “Although it is widely believed that increasing atmospheric CO2 levels will cause noticeable global warming, the effects are not yet detectable, possibly because of the ‘noise’ of natural climatic variability. An examination of the spatial and seasonal distribution of signal-to-noise ratio shows that the highest values occur in summer and annual mean surface temperatures averaged over the Northern Hemisphere or over mid-latitudes. The spatial and seasonal characteristics of the early twentieth century warming were similar to those expected from increasing CO2 based on an equilibrium response model. This similarity may hinder the early detection of CO2 effects on climate.” T. M. L. Wigley & P. D. Jones, Nature 292, 205 – 208 (16 July 1981); doi:10.1038/292205a0.

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