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Observations of anthropogenic global warming

Archive for March, 2010

Papers on formal attribution

Posted by Ari Jokimäki on March 25, 2010

This is a list of papers on formal attribution which means papers attributing the climate change to specific causes. This list was compiled by Jesús Rosino and was originally published here. With his permission, I’m publishing the list here in English and in my usual format. As my contribution to this list is merely to edit it to my format (and I added the Pierce et al. 2006 paper), this basically is a guest post by Jesús Rosino. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (March 25, 2018): Hegerl et al. (1997), Jones et al. (2016), and Jones & Kennedy (2017) added.
UPDATE (February 25, 2016): Huber & Knutti (2012), Gillett et al. (2012), Wigley & Santer (2013), and Jones et al. (2013) added. Thanks to Keith Pickering for pointing them out. Also some dead links corrected.
UPDATE (August 7, 2010): Andronova & Schlesinger (2000), Barnett et al. (1999), and North & Stevens (1998) added; couple of full text links added; broken links corrected. Thanks to Barry for providing information on all of these, see the comment section below.
UPDATE (April 11, 2010): Schneider (1994) added.

Sensitivity of Attribution of Anthropogenic Near-Surface Warming to Observational Uncertainty – Jones & Kennedy (2017)
Abstract: The impact of including comprehensive estimates of observational uncertainties on a detection and attribution analysis of twentieth-century near-surface temperature variations is investigated. The error model of HadCRUT4, a dataset of land near-surface air temperatures and sea surface temperatures, provides estimates of measurement, sampling, and bias adjustment uncertainties. These uncertainties are incorporated into an optimal detection analysis that regresses simulated large-scale temporal and spatial variations in near-surface temperatures, driven by well-mixed greenhouse gas variations and other anthropogenic and natural factors, against observed changes. The inclusion of bias adjustment uncertainties increases the variance of the regression scaling factors and the range of attributed warming from well-mixed greenhouse gases by less than 20%. Including estimates of measurement and sampling errors has a much smaller impact on the results. The range of attributable greenhouse gas warming is larger across analyses exploring dataset structural uncertainty. The impact of observational uncertainties on the detection analysis is found to be small compared to other sources of uncertainty, such as model variability and methodological choices, but it cannot be ruled out that on different spatial and temporal scales this source of uncertainty may be more important. The results support previous conclusions that there is a dominant anthropogenic greenhouse gas influence on twentieth-century near-surface temperature increases.
Citation: Jones, G.S. and J.J. Kennedy, 2017: Sensitivity of Attribution of Anthropogenic Near-Surface Warming to Observational Uncertainty. J. Climate, 30, 4677–4691,

Uncertainties in the attribution of greenhouse gas warming and implications for climate prediction – Jones et al. (2016)
Abstract: Using optimal detection techniques with climate model simulations, most of the observed increase of near‐surface temperatures over the second half of the twentieth century is attributed to anthropogenic influences. However, the partitioning of the anthropogenic influence to individual factors, such as greenhouse gases and aerosols, is much less robust. Differences in how forcing factors are applied, in their radiative influence and in models’ climate sensitivities, substantially influence the response patterns. We find that standard optimal detection methodologies cannot fully reconcile this response diversity. By selecting a set of experiments to enable the diagnosing of greenhouse gases and the combined influence of other anthropogenic and natural factors, we find robust detections of well‐mixed greenhouse gases across a large ensemble of models. Of the observed warming over the twentieth century of 0.65 K/century we find, using a multimodel mean not incorporating pattern uncertainty, a well‐mixed greenhouse gas warming of 0.87 to 1.22 K/century. This is partially offset by cooling from other anthropogenic and natural influences of −0.54 to −0.22 K/century. Although better constrained than recent studies, the attributable trends across climate models are still wide, with implications for observational constrained estimates of transient climate response. Some of the uncertainties could be reduced in future by having more model data to better quantify the simulated estimates of the signals and natural variability, by designing model experiments more effectively and better quantification of the climate model radiative influences. Most importantly, how model pattern uncertainties are incorporated into the optimal detection methodology should be improved.
Citation: Jones, G. S., P. A. Stott, and J. F. B.‐Mitchell (2016), Uncertainties in the attribution of greenhouse gas warming and implications for climate prediction, J. Geophys. Res. Atmos., 121, 6969–6992, doi:10.1002/2015JD024337. [Full text]

Attribution of observed historical near‒surface temperature variations to anthropogenic and natural causes using CMIP5 simulations – Jones et al. (2013)
Abstract: We have carried out an investigation into the causes of changes in near‒surface temperatures from 1860 to 2010. We analyze the HadCRUT4 observational data set which has the most comprehensive set of adjustments available to date for systematic biases in sea surface temperatures and the CMIP5 ensemble of coupled models which represents the most sophisticated multi‒model climate modeling exercise yet carried out. Simulations that incorporate both anthropogenic and natural factors span changes in observed temperatures between 1860 and 2010, while simulations of natural factors do not warm as much as observed. As a result of sampling a much wider range of structural modeling uncertainty, we find a wider spread of historic temperature changes in CMIP5 than was simulated by the previous multi‒model ensemble, CMIP3. However, calculations of attributable temperature trends based on optimal detection support previous conclusions that human‒induced greenhouse gases dominate observed global warming since the mid‒20th century. With a much wider exploration of model uncertainty than previously carried out, we find that individually the models give a wide range of possible counteracting cooling from the direct and indirect effects of aerosols and other non‒greenhouse gas anthropogenic forcings. Analyzing the multi‒model mean over 1951–2010 (focusing on the most robust result), we estimate a range of possible contributions to the observed warming of approximately 0.6 K from greenhouse gases of between 0.6 and 1.2 K, balanced by a counteracting cooling from other anthropogenic forcings of between 0 and −0.5 K.
Citation: Jones, G. S., P. A. Stott, and N. Christidis (2013), Attribution of observed historical near‒surface temperature variations to anthropogenic and natural causes using CMIP5 simulations, J. Geophys. Res. Atmos., 118, 4001–4024, doi:10.1002/jgrd.50239. [Full text]

A probabilistic quantification of the anthropogenic component of twentieth century global warming – Wigley & Santer (2013)
Abstract: This paper examines in detail the statement in the 2007 IPCC Fourth Assessment Report that “Most of the observed increase in global average temperatures since the mid-twentieth century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations”. We use a quantitative probabilistic analysis to evaluate this IPCC statement, and discuss the value of the statement in the policy context. For forcing by greenhouse gases (GHGs) only, we show that there is a greater than 90 % probability that the expected warming over 1950–2005 is larger than the total amount (not just “most”) of the observed warming. This is because, following current best estimates, negative aerosol forcing has substantially offset the GHG-induced warming. We also consider the expected warming from all anthropogenic forcings using the same probabilistic framework. This requires a re-assessment of the range of possible values for aerosol forcing. We provide evidence that the IPCC estimate for the upper bound of indirect aerosol forcing is almost certainly too high. Our results show that the expected warming due to all human influences since 1950 (including aerosol effects) is very similar to the observed warming. Including the effects of natural external forcing factors has a relatively small impact on our 1950–2005 results, but improves the correspondence between model and observations over 1900–2005. Over the longer period, however, externally forced changes are insufficient to explain the early twentieth century warming. We suggest that changes in the formation rate of North Atlantic Deep Water may have been a significant contributing factor.
Citation: T. M. L. Wigley, B. D. Santer (2013), Climate Dynamics, March 2013, Volume 40, Issue 5, pp 1087-1102, doi:10.1007/s00382-012-1585-8. [Full text]

Improved constraints on 21st-century warming derived using 160 years of temperature observations – Gillett et al. (2012)
Abstract: Projections of 21st century warming may be derived by using regression-based methods to scale a model’s projected warming up or down according to whether it under- or over-predicts the response to anthropogenic forcings over the historical period. Here we apply such a method using near surface air temperature observations over the 1851–2010 period, historical simulations of the response to changing greenhouse gases, aerosols and natural forcings, and simulations of future climate change under the Representative Concentration Pathways from the second generation Canadian Earth System Model (CanESM2). Consistent with previous studies, we detect the influence of greenhouse gases, aerosols and natural forcings in the observed temperature record. Our estimate of greenhouse-gas-attributable warming is lower than that derived using only 1900–1999 observations. Our analysis also leads to a relatively low and tightly-constrained estimate of Transient Climate Response of 1.3–1.8°C, and relatively low projections of 21st-century warming under the Representative Concentration Pathways. Repeating our attribution analysis with a second model (CNRM-CM5) gives consistent results, albeit with somewhat larger uncertainties.
Citation: Gillett, N. P., V. K. Arora, G. M. Flato, J. F. Scinocca, and K. vonSalzen (2012), Improved constraints on 21st-century warming derived using 160 years of temperature observations, Geophys. Res. Lett., 39, L01704, doi:10.1029/2011GL050226. [Full text]

Anthropogenic and natural warming inferred from changes in Earth’s energy balance – Huber & Knutti (2012)
Abstract: The Earth’s energy balance is key to understanding climate and climate variations that are caused by natural and anthropogenic changes in the atmospheric composition. Despite abundant observational evidence for changes in the energy balance over the past decades, the formal detection of climate warming and its attribution to human influence has so far relied mostly on the difference between spatio-temporal warming patterns of natural and anthropogenic origin. Here we present an alternative attribution method that relies on the principle of conservation of energy, without assumptions about spatial warming patterns. Based on a massive ensemble of simulations with an intermediate-complexity climate model we demonstrate that known changes in the global energy balance and in radiative forcing tightly constrain the magnitude of anthropogenic warming. We find that since the mid-twentieth century, greenhouse gases contributed 0.85 °C of warming (5–95% uncertainty: 0.6–1.1 °C), about half of which was offset by the cooling effects of aerosols, with a total observed change in global temperature of about 0.56 °C. The observed trends are extremely unlikely (<5%) to be caused by internal variability, even if current models were found to strongly underestimate it. Our method is complementary to optimal fingerprinting attribution and produces fully consistent results, thus suggesting an even higher confidence that human-induced causes dominate the observed warming.
Citation: Markus Huber & Reto Knutti (2012), Nature Geoscience 5, 31–36, doi:10.1038/ngeo1327. [Full text]

Anthropogenic forcing dominates sea level rise since 1850 – Jevrejeva et al. (2009)
Abstract: “Here we use a delayed response statistical model to attribute the past 1000 years of sea level variability to various natural (volcanic and solar radiative) and anthropogenic (greenhouse gases and aerosols) forcings. We show that until 1800 the main drivers of sea level change are volcanic and solar radiative forcings. For the past 200 years sea level rise is mostly associated with anthropogenic factors. Only 4 ± 1.5 cm (25% of total sea level rise) during the 20th century is attributed to natural forcings, the remaining 14 ± 1.5 cm are due to a rapid increase in CO2 and other greenhouse gases.” [Full text]

A Multimodel Update on the Detection and Attribution of Global Surface Warming – Stone et al.
Abstract: (2007)
“This paper presents an update on the detection and attribution of global annual mean surface air temperature changes, using recently developed climate models. … Greenhouse gas and solar irradiance changes are found to have contributed to a best guess of ~0.8 and ~0.3 K warming over the 1901–2005 period, respectively, while sulfate aerosols have contributed a ~0.4 K cooling.” [Full text]

The Detection and Attribution of Climate Change Using an Ensemble of Opportunity – Stone et al. (2007)
Abstract: “This paper presents an extension to the fingerprinting technique that permits the inclusion of GCMs in the multisignal analysis of surface temperature even when the required families of ensembles have not been generated. … The result is that the temperature difference of the 1996–2005 decade relative to the 1940–49 decade can be attributed to greenhouse gas emissions, with a partially offsetting cooling from sulfate emissions and little contribution from natural sources.” [Full text]

Anthropogenic Warming of the Oceans: Observations and Model Results – Pierce et al. (2006)
Abstract: “Comparing the observations with results from two coupled ocean–atmosphere climate models [the Parallel Climate Model version 1 (PCM) and the Hadley Centre Coupled Climate Model version 3 (HadCM3)] that include anthropogenic forcing shows remarkable agreement between the observed and model-estimated warming. … In the top 100 m of the water column the warming is well separated from natural variability, including both variability arising from internal instabilities of the coupled ocean–atmosphere climate system and that arising from volcanism and solar fluctuations. … The observed sampling of ocean temperature is highly variable in space and time, but sufficient to detect the anthropogenic warming signal in all basins, at least in the surface layers, by the 1980s.” [Full text]

Detecting and Attributing External Influences on the Climate System: A Review of Recent Advances – The International Ad Hoc Detection and Attribution Group (2005)
A review paper. Abstract: “This paper reviews recent research that assesses evidence for the detection of anthropogenic and natural external influences on the climate. … These observed climate changes are very unlikely to be due only to natural internal climate variability, and they are consistent with the responses to anthropogenic and natural external forcing of the climate system that are simulated with climate models. The evidence indicates that natural drivers such as solar variability and volcanic activity are at most partially responsible for the large-scale temperature changes observed over the past century, and that a large fraction of the warming over the last 50 yr can be attributed to greenhouse gas increases. Thus, the recent research supports and strengthens the IPCC Third Assessment Report conclusion that “most of the global warming over the past 50 years is likely due to the increase in greenhouse gases.”” [Full text]

Combinations of Natural and Anthropogenic Forcings in Twentieth-Century Climate – Meehl et al. (2004)
Abstract: “Ensemble simulations are run with a global coupled climate model employing five forcing agents that influence the time evolution of globally averaged surface air temperature during the twentieth century. … The late-twentieth-century warming can only be reproduced in the model with anthropogenic forcing (mainly GHGs), while the early twentieth-century warming is mainly caused by natural forcing in the model (mainly solar).” [Full text]

Causes of atmospheric temperature change 1960–2000: A combined attribution analysis – Jones et al. (2003)
Abstract: “We investigate the causes of temperature change over the last four decades, both near the surface and in the free atmosphere, using a coupled atmosphere/ocean general circulation model, HadCM3, which requires no flux correction. … Our results strengthen the case for an anthropogenic influence on climate. Unlike previous studies we attribute observed decadal-mean temperature changes both to anthropogenic emissions, and changes in stratospheric volcanic aerosols. The temperature response to change in solar irradiance is also detected but with a lower confidence than the other forcings.” [Full text]

Modern Global Climate Change – Karl & Trenberth (2003)
Abstract: “Modern climate change is dominated by human influences, which are now large enough to exceed the bounds of natural variability. The main source of global climate change is human-induced changes in atmospheric composition. These perturbations primarily result from emissions associated with energy use, but on local and regional scales, urbanization and land use changes are also important.” [Full text]

Estimation of natural and anthropogenic contributions to twentieth century temperature change – Tett et al. (2002)
Abstract: “Using a coupled atmosphere/ocean general circulation model, we have simulated the climatic response to natural and anthropogenic forcings from 1860 to 1997. … 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. … 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.” [FULL TEXT]

Detection of Anthropogenic Climate Change in the World’s Oceans – Barnett et al. (2001)
Abstract: “Large-scale increases in the heat content of the world’s oceans have been observed to occur over the last 45 years. The horizontal and temporal character of these changes has been closely replicated by the state-of-the-art Parallel Climate Model (PCM) forced by observed and estimated anthropogenic gases. … This suggests that the observed ocean heat-content changes are consistent with those expected from anthropogenic forcing, which broadens the basis for claims that an anthropogenic signal has been detected in the global climate system.”

Attribution of twentieth century temperature change to natural and anthropogenic causes – Stott et al. (2001)
Abstract: “We analyse possible causes of twentieth century near-surface temperature change. We use an “optimal detection” methodology to compare seasonal and annual data from the coupled atmosphere-ocean general circulation model HadCM2 with observations averaged over a range of spatial and temporal scales. The results indicate that the increases in temperature observed in the latter half of the century have been caused by warming from anthropogenic increases in greenhouse gases offset by cooling from tropospheric sulfate aerosols rather than natural variability, either internal or externally forced. We also find that greenhouse gases are likely to have contributed significantly to the warming in the first half of the century.”

Causes of global temperature changes during the 19th and 20th centuries – Andronova & Schlesinger (2000)
Abstract: “During the past two decades there has been considerable discussion about the relative contribution of different factors to the temperature changes observed now over the past 142 years. Among these factors are the “external’ factors of human (anthropogenic) activity, volcanoes and putative variations in the irradiance of the sun, and the “internal” factor of natural variability. Here, by using a simple climate/ocean model to simulate the observed temperature changes for different state‐of‐the‐art radiative‐forcing models, we present strong evidence that while the anthropogenic effect has steadily increased in size during the entire 20th century such that it presently is the dominant external forcing of the climate system, there is a residual factor at work within the climate system, whether a natural oscillation or something else as yet unknown. This has an important implication for our expectation of future temperature changes.”

Causes of Climate Change Over the Past 1000 Years – Crowley (2000)
Abstract: “Recent reconstructions of Northern Hemisphere temperatures and climate forcing over the past 1000 years allow the warming of the 20th century to be placed within a historical context and various mechanisms of climate change to be tested. … The combination of a unique level of temperature increase in the late 20th century and improved constraints on the role of natural variability provides further evidence that the greenhouse effect has already established itself above the level of natural variability in the climate system. A 21st-century global warming projection far exceeds the natural variability of the past 1000 years and is greater than the best estimate of global temperature change for the last interglacial.” [Full text]

Anthropogenic and natural causes of twentieth century temperature change – Stott et al. (2000)
Abstract: “We analyse spatio-temporal patterns of near-surface temperature change to provide an attribution of twentieth century climate change. We apply an “optimal detection” methodology to seasonal and annual data averaged over a range of spatial and temporal scales. We find that solar effects may have contributed significantly to the warming in the first half of the century although this result is dependent on the reconstruction of total solar irradiance that is used. In the latter half of the century, we find that anthropogenic increases in greenhouses gases are largely responsible for the observed warming, balanced by some cooling due to anthropogenic sulphate aerosols, with no evidence for significant solar effects.”

External Control of 20th Century Temperature by Natural and Anthropogenic Forcings – Stott et al. (2000)
Abstract: “A comparison of observations with simulations of a coupled ocean-atmosphere general circulation model shows that both natural and anthropogenic factors have contributed significantly to 20th century temperature changes. … Natural forcings were relatively more important in the early-century warming and anthropogenic forcings have played a dominant role in warming observed in recent decades. … Anthropogenic global warming under a standard emissions scenario is predicted to continue at a rate similar to that observed in recent decades.” [Full text] [Perspective]

Detection and Attribution of Recent Climate Change: A Status Report – Barnett et al. (1999)
Abstract: “This paper addresses the question of where we now stand with respect to detection and attribution of an anthropogenic climate signal. Our ability to estimate natural climate variability, against which claims of anthropogenic signal detection must be made, is reviewed. The current situation suggests control runs of global climate models may give the best estimates of natural variability on a global basis, estimates that appear to be accurate to within a factor of 2 or 3 at multidecadal timescales used in detection work. … Most, but not all, results suggest that recent changes in global climate inferred from surface air temperature are likely not due solely to natural causes. At present it is not possible to make a very confident statement about the relative contributions of specific natural and anthropogenic forcings to observed climate change. One of the main reasons is that fully realistic simulations of climate change due to the combined effects of all anthropogenic and natural forcings mechanisms have yet to be computed.” [Full text]

Causes of twentieth-century temperature change near the Earth’s surface – Tett et al. (1999)
Abstract: “Here we present a quantification of the possible contributions throughout the century from the four components most likely to be responsible for the large-scale temperature changes, of which two vary naturally (solar irradiance and stratospheric volcanic aerosols) and two have changed decisively due to anthropogenic influence (greenhouse gases and sulphate aerosols). The patterns of time/space changes in near-surface temperature due to the separate forcing components are simulated with a coupled atmosphere–ocean general circulation model, and a linear combination of these is fitted to observations. … For the warming from 1946 to 1996 regardless of any possible amplification of solar or volcanic influence, we exclude purely natural forcing, and attribute it largely to the anthropogenic components.”

Detecting Climate Signals in the Surface Temperature Record – North & Stevens (1998)
Abstract: “Optimal signal detection theory has been applied in a search through 100 yr of surface temperature data for the climate response to four specific radiative forcings. The data used comes from 36 boxes on the earth and was restricted to the frequency band 0.06–0.13 cycles yr−1 (16.67–7.69 yr) in the analysis. Estimates were sought of the strengths of the climate response to solar variability, volcanic aerosols, greenhouse gases, and anthropogenic aerosols. … Results are reasonably consistent across these four separate model formulations. It was found that the component of the volcanic response perpendicular to the other signals was very robust and highly significant. Similarly, the component of the greenhouse gas response perpendicular to the others was very robust and highly significant. When the sum of all four climate forcings was used, the climate response was more than three standard deviations above the noise level. These findings are considered to be powerful evidence of anthropogenically induced climate change.” [Full text]

Multi-fingerprint detection and attribution analysis of greenhouse gas, greenhouse gas-plus-aerosol and solar forced climate change – Hegerl et al. (1997)
Abstract: A multi-fingerprint analysis is applied to the detection and attribution of anthropogenic climate change. While a single fingerprint is optimal for the detection of climate change, further tests of the statistical consistency of the detected climate change signal with model predictions for different candidate forcing mechanisms require the simultaneous application of several fingerprints. Model-predicted climate change signals are derived from three anthropogenic global warming simulations for the period 1880 to 2049 and two simulations forced by estimated changes in solar radiation from 1700 to 1992. In the first global warming simulation, the forcing is by greenhouse gas only, while in the remaining two simulations the direct influence of sulfate aerosols is also included. From the climate change signals of the greenhouse gas only and the average of the two greenhouse gas-plus-aerosol simulations, two optimized fingerprint patterns are derived by weighting the model-predicted climate change patterns towards low-noise directions. The optimized fingerprint patterns are then applied as a filter to the observed near-surface temperature trend patterns, yielding several detection variables. The space-time structure of natural climate variability needed to determine the optimal fingerprint pattern and the resultant signal-to-noise ratio of the detection variable is estimated from several multi-century control simulations with different CGCMs and from instrumental data over the last 136 y. Applying the combined greenhouse gas-plus-aerosol fingerprint in the same way as the greenhouse gas only fingerprint in a previous work, the recent 30-y trends (1966–1995) of annual mean near surface temperature are again found to represent a significant climate change at the 97.5% confidence level. However, using both the greenhouse gas and the combined forcing fingerprints in a two-pattern analysis, a substantially better agreement between observations and the climate model prediction is found for the combined forcing simulation. Anticipating that the influence of the aerosol forcing is strongest for longer term temperature trends in summer, application of the detection and attribution test to the latest observed 50-y trend pattern of summer temperature yielded statistical consistency with the greenhouse gas-plus-aerosol simulation with respect to both the pattern and amplitude of the signal. In contrast, the observations are inconsistent with the greenhouse-gas only climate change signal at a 95% confidence level for all estimates of climate variability. The observed trend 1943–1992 is furthermore inconsistent with a hypothesized solar radiation change alone at an estimated 90% confidence level. Thus, in contrast to the single pattern analysis, the two pattern analysis is able to discriminate between different forcing hypotheses in the observed climate change signal. The results are subject to uncertainties associated with the forcing history, which is poorly known for the solar and aerosol forcing, the possible omission of other important forcings, and inevitable model errors in the computation of the response to the forcing. Further uncertainties in the estimated significance levels arise from the use of model internal variability simulations and relatively short instrumental observations (after subtraction of an estimated greenhouse gas signal) to estimate the natural climate variability. The resulting confidence limits accordingly vary for different estimates using different variability data. Despite these uncertainties, however, we consider our results sufficiently robust to have some confidence in our finding that the observed climate change is consistent with a combined greenhouse gas and aerosol forcing, but inconsistent with greenhouse gas or solar forcing alone.
Citation: Hegerl, G., Hasselmann, K., Cubasch, U. et al. Climate Dynamics (1997) 13: 613. [Full text]

A search for human influences on the thermal structure of the atmosphere – Santer et al. (1996)
Abstract: “The observed spatial patterns of temperature change in the free atmosphere from 1963 to 1987 are similar to those predicted by state-of-the-art climate models incorporating various combinations of changes in carbon dioxide, anthropogenic sulphate aerosol and stratospheric ozone concentrations. The degree of pattern similarity between models and observations increases through this period. It is likely that this trend is partially due to human activities, although many uncertainties remain, particularly relating to estimates of natural variability.” [Full text]

Detecting Climatic Change Signals: Are There Any “Fingerprints”? – Schneider (1994)
Abstract: “Until climate models are driven by time-evolving, combined, multiple, and heterogeneous forcing factors, the best global climatic change “fingerprint” will probably remain a many-decades average of hemi-spheric- to global-scale trends in surface air temperatures. Century-long global warming (or cooling) trends of 0.5°C appear to have occurred infrequently over the past several thousand years—perhaps only once or twice a millennium, as proxy records suggest. This implies an 80 to 90 percent heuristic likelihood that the 20th-century 0.5 ± 0.2°C warming trend is not a wholly natural climatic fluctuation.”

Attribution of regional-scale climate change

Detection and attribution of climate change: a regional perspective – Stott et al. (2010)
Abstract: “This paper reviews this evidence from a regional perspective to reflect a growing interest in understanding the regional effects of climate change, which can differ markedly across the globe. We set out the methodological basis for detection and attribution and discuss the spatial scales on which it is possible to make robust attribution statements. We review the evidence showing significant human-induced changes in regional temperatures, and for the effects of external forcings on changes in the hydrological cycle, the cryosphere, circulation changes, oceanic changes, and changes in extremes.” [Full text]

Attribution of polar warming to human influence – Gillett et al. (2008)
Abstract: “Here we use an up-to-date gridded data set of land surface temperatures and simulations from four coupled climate models to assess the causes of the observed polar temperature changes. We find that the observed changes in Arctic and Antarctic temperatures are not consistent with internal climate variability or natural climate drivers alone, and are directly attributable to human influence. Our results demonstrate that human activities have already caused significant warming in both polar regions, with likely impacts on polar biology, indigenous communities, ice-sheet mass balance and global sea level.” [Full text]

Detection of a Human Influence on North American Climate – Karoly et al. (2003)
Abstract: “Several indices of large-scale patterns of surface temperature variation were used to investigate climate change in North America over the 20th century. The observed variability of these indices was simulated well by a number of climate models. Comparison of index trends in observations and model simulations shows that North American temperature changes from 1950 to 1999 were unlikely to be due to natural climate variation alone. Observed trends over this period are consistent with simulations that include anthropogenic forcing from increasing atmospheric greenhouse gases and sulfate aerosols. However, most of the observed warming from 1900 to 1949 was likely due to natural climate variation.” [Full text]

Attribution of regional-scale temperature changes to anthropogenic and natural causes – Stott (2003)
Abstract: “The causes of twentieth century temperature change in six separate land areas of the Earth have been determined by carrying out a series of optimal detection analyses. The warming effects of increasing greenhouse gas concentrations have been detected in all the regions examined, including North America and Europe. In most regions, cooling from sulfate aerosols counteracts some of the greenhouse warming, and there is some evidence for reduced net aerosol cooling in Asia, possibly as a result of warming from black carbon.” [Full text]


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Papers on ecosystem response to past climate

Posted by Ari Jokimäki on March 22, 2010

This is a list of papers on ecosystem response to past climate changes. This subject was suggested by J Bowers in this thread. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (June 10, 2010): Root et al. (2003) added.
UPDATE (May 22, 2010): Woolridge (2008) added, thanks to J Bowers for pointing it out (see the comment section below).

Fossil Plant Relative Abundances Indicate Sudden Loss of Late Triassic Biodiversity in East Greenland – McElwain et al. (2009) “The pace of Late Triassic (LT) biodiversity loss is uncertain, yet it could help to decipher causal mechanisms of mass extinction. We investigated relative abundance distributions (RADs) of six LT plant assemblages from the Kap Stewart Group, East Greenland, to determine the pace of collapse of LT primary productivity. RADs displayed not simply decreases in the number of taxa, but decreases in the number of common taxa. Likelihood tests rejected a hypothesis of continuously declining diversity. Instead, the RAD shift occurred over the upper two-to-four fossil plant assemblages and most likely over the last three (final 13 meters), coinciding with increased atmospheric carbon dioxide concentration and global warming. Thus, although the LT event did not induce mass extinction of plant families, it accompanied major and abrupt change in their ecology and diversity. “ [Full text]

A long-term association between global temperature and biodiversity, origination and extinction in the fossil record – Mayhew et al. (2008) “We analysed the fossil record for the last 520 Myr against estimates of low latitude sea surface temperature for the same period. We found that global biodiversity (the richness of families and genera) is related to temperature and has been relatively low during warm ‘greenhouse’ phases, while during the same phases extinction and origination rates of taxonomic lineages have been relatively high. These findings are consistent for terrestrial and marine environments and are robust to a number of alternative assumptions and potential biases. Our results provide the first clear evidence that global climate may explain substantial variation in the fossil record in a simple and consistent manner.” [Full text]

The palaeoclimatology, palaeoecology and palaeoenvironmental analysis of mass extinction events – Twitchett (2006) “Many aspects of these [mass extinction] events are still debated and there is no common cause or single set of climatic or environmental changes common to these five events, although all are associated with evidence for climatic change. … The environmental consequences of rapid global warming (such as ocean stagnation, reduced upwelling and loss of surface productivity) are considered to have been particularly detrimental to the biosphere in the geological past. The first phase of the Late Ordovician event is clearly linked to rapid global cooling.” [Full text]

Nannoplankton Extinction and Origination Across the Paleocene-Eocene Thermal Maximum – Gibbs et al. (2006) “The Paleocene-Eocene Thermal Maximum (PETM, 55 million years ago) was an interval of global warming and ocean acidification attributed to rapid release and oxidation of buried carbon. We show that the onset of the PETM coincided with a prominent increase in the origination and extinction of calcareous phytoplankton. Yet major perturbation of the surface-water saturation state across the PETM was not detrimental to the survival of most calcareous nannoplankton taxa and did not impart a calcification or ecological bias to the pattern of evolutionary turnover. Instead, the rate of environmental change appears to have driven turnover, preferentially affecting rare taxa living close to their viable limits.” [Full text]

Exceptional record of mid-Pleistocene vertebrates helps differentiate climatic from anthropogenic ecosystem perturbations – Barnosky et al. (2004) “We report on a uniquely rich mid-Pleistocene vertebrate sequence from Porcupine Cave, Colorado, which records at least 127 species and the earliest appearances of 30 mammals and birds. By analyzing >20,000 mammal fossils in relation to modern species and independent climatic proxies, we determined how mammal communities reacted to presumed glacial–interglacial transitions between 1,000,000 and 600,000 years ago. We conclude that climatic warming primarily affected mammals of lower trophic and size categories, in contrast to documented human impacts on higher trophic and size categories historically. Despite changes in species composition and minor changes in small-mammal species richness evident at times of climatic change, overall structural stability of mammal communities persisted >600,000 years before human impacts.” [Full text]

Did impacts, volcanic eruptions, or climate change affect mammalian evolution? – Prothero (2004) “Two different Cenozoic mammal diversity curves were compared, and important climatic, volcanic, and impact horizons were examined in detail. In no case is there a strong correlation between impacts, eruptions, or climatic events and any episode of mammalian turnover. On the contrary, most of the known impact, eruption, and climatic events of the Cenozoic occurred during intervals of faunal stability. Conversely, episodes of high turnover and faunal change among Cenozoic mammals correlate with no known extrinsic causes. Apparently, extrinsic environmental factors such as impacts, eruptions, and climate change have a minimal effect, and intrinsic biological factors must be more important.”

How to kill (almost) all life: the end-Permian extinction event – Benton & Twitchett (2003) “The biggest mass extinction of the past 600 million years (My), the end-Permian event (251 My ago), witnessed the loss of as much as 95% of all species on Earth. Key questions for biologists concern what combination of environmental changes could possibly have had such a devastating effect, the scale and pattern of species loss, and the nature of the recovery. New studies on dating the event, contemporary volcanic activity, and the anatomy of the environmental crisis have changed our perspectives dramatically in the past five years. Evidence on causation is equivocal, with support for either an asteroid impact or mass volcanism, but the latter seems most probable. The extinction model involves global warming by 6°C and huge input of light carbon into the ocean-atmosphere system from the eruptions, but especially from gas hydrates, leading to an ever-worsening positive-feedback loop, the ‘runaway greenhouse’.” [Full text]

Correlated terrestrial and marine evidence for global climate changes before mass extinction at the Cretaceous–Paleogene boundary – Wilf et al. (2003) “Both plants and foraminifera indicate warming near 66.0 Ma, a warming peak from ≈65.8 to 65.6 Ma, and cooling near 65.6 Ma, suggesting that these were global climate shifts. The warming peak coincides with the immigration of a thermophilic flora, maximum plant diversity, and the poleward range expansion of thermophilic foraminifera. … To the extent that biodiversity is correlated with temperature, estimates of the severity of end-Cretaceous extinctions that are based on occurrence data from the warming peak are probably inflated, as we illustrate for North Dakota plants. However, our analysis of climate and facies considerations shows that the effects of bolide impact should be regarded as the most significant contributor to these plant extinctions.” [Full text]

Mammalian Response to Global Warming on Varied Temporal Scales – Barnosky et al. (2003) “Paleontological information was used to evaluate and compare how Rocky Mountain mammalian communities changed during past global warming events characterized by different durations (350, ;10,000–20,000, and 4 million years) and different per–100-year warming rates (1.08C, 0.18C, 0.06–0.088C, 0.0002–0.00038C per 100 years). … Nevertheless, examination of past global warming episodes suggested that approximately concurrent with warming, a predictable sequence of biotic events occurs at the regional scale of the central and northern United States Rocky Mountains. First, phenotypic and density changes in populations are detectable within 100 years. Extinction of some species, noticeable changes in taxonomic composition of communities, and possibly reduction in species richness follow as warming extends to a few thousand years. Faunal turnover nears 100% and species diversity may increase when warm temperatures last hundreds of thousands to millions of years, because speciation takes place and faunal changes initiated by a variety of shorter-term processes accumulate. Climate-induced faunal changes reported for the current global warming episode probably do not yet exceed the normal background rate, but continued warming during the next few decades, especially combined with the many other pressures of humans on natural ecosystems, has a high probability of producing effects that have not been experienced often, if ever, in mammalian history.” [Full text]

Fingerprints of global warming on wild animals and plants – Root et al. (2003) “We gathered information on species and global warming from 143 studies for our meta-analyses. These analyses reveal a consistent temperature-related shift, or ‘fingerprint’, in species ranging from molluscs to mammals and from grasses to trees. Indeed, more than 80% of the species that show changes are shifting in the direction expected on the basis of known physiological constraints of species. Consequently, the balance of evidence from these studies strongly suggests that a significant impact of global warming is already discernible in animal and plant populations.”

Earth’s biggest ‘whodunnit’: unravelling the clues in the case of the end–Permian mass extinction – White (2002) “The mass extinction that occurred at the end of the Permian period, 250 million years ago, was the most devastating loss of life that Earth has ever experienced. It is estimated that ca. 96% of marine species were wiped out and land plants, reptiles, amphibians and insects also suffered. The causes of this catastrophic event are currently a topic of intense debate. The geological record points to significant environmental disturbances, for example, global warming and stagnation of ocean water.” [Full text]

Global Climate Change and North American Mammalian Evolution – Alroy et al. (2000) “We compare refined data sets for Atlantic benthic foraminiferal oxygen isotope ratios and for North American mammalian diversity, faunal turnover, and body mass distributions. Each data set spans the late Paleocene through Pleistocene and has temporal resolution of 1.0 m.y. … Some of the major climate shifts indicated by oxygen isotope records do correspond to major ecological and evolutionary transitions in the mammalian biota, but the nature of these correspondences is unpredictable, and several other such transitions occur at times of relatively little global climate change. We conclude that given currently available climate records, we cannot show that the impact of climate change on the broad patterns of mammalian evolution involves linear forcings; instead, we see only the relatively unpredictable effects of a few major events.” [Full text]

Fossil Plants and Global Warming at the Triassic-Jurassic Boundary – McElwain et al. (1999) “The Triassic-Jurassic boundary marks a major faunal mass extinction, but records of accompanying environmental changes are limited. Paleobotanical evidence indicates a fourfold increase in atmospheric carbon dioxide concentration and suggests an associated 3° to 4°C “greenhouse” warming across the boundary. These environmental conditions are calculated to have raised leaf temperatures above a highly conserved lethal limit, perhaps contributing to the >95 percent species-level turnover of Triassic-Jurassic megaflora.”

Abrupt Climate Change and Extinction Events in Earth History – Crowley & North (1988) “There is a growing body of theoretical and empirical support for the concept of abrupt climate change, and a comparison of paleoclimate data with the Phanerozoic extinction record indicates that climate and biotic transitions often coincide. … Our analysis suggests that a terrestrially induced climate instability is a viable mechanism for causing rapid environmental change and biotic turnover in earth history, but the relation is not so strong that other sources of variance can be excluded.” [Full text]

Temperature and biotic crises in the marine realm – Stanley (1984) “Climatic change has been a prominent cause of marine mass extinction, but areal restriction of seafloor during global regression has not. Late Eocene and Pliocene-Pleistocene cooling, for example, caused major extinctions, but profound global Oligocene and Pleistocene regressions had little or no direct effect on benthic diversity. Recurrent themes of pre-Cenozoic marine crises suggest that global temperature change also served as a major, and perhaps dominant, agent of extinction in these events: (1) Mass extinctions have frequently been concentrated in the tropics, which seem to have become a refrigerated trap from which there has been no escape; biotas previously occupying high latitudes have shifted equatorward, to replace disappearing tropical biotas. (2) Some crises were not instantaneous but followed protracted and pulsatile temporal patterns, as would be predicted for complex, global climatic crises. (3) Several mass extinctions coincided with recognized intervals of climatic cooling.”

Closely related

Mass extinctions past and present: a unifying hypothesis – Woolridge (2008) Note that the peer review of this paper was interrupted (see the interactive discussion linked in the abstract page) but I include this paper to show this hypothesis. “Here, it is proposed that the pH-dependent inactivation of a single enzyme, urease, provides a unifying kill-mechanism for at least four of the “big five” mass extinctions of the past 560 million years. The triggering of this kill-mechanism is suggested to be sensitive to both gradualistic and catastrophic environmental disturbances that cause the operating pH of urease-dependent organisms to cross enzymatic “dead zones”, one of which is suggested to exist at ~pH 7.9. For a wide range of oceanic and terrestrial ecosystems, this pH threshold coincides with an atmospheric CO2 partial pressure (pCO2) of ~560 ppmv – a level that at current CO2 emission trajectories may be exceeded as early as 2050.” [Full text]

Documenting a significant relationship between macroevolutionary origination rates and Phanerozoic pCO2 levels – Cornette et al. (2002) “We show that the rates of diversification of the marine fauna and the levels of atmospheric CO2 have been closely correlated for the past 545 million years. … The strength of the correlation suggests that one or more environmental variables controlling CO2 levels have had a profound impact on evolution throughout the history of metazoan life.” [Full text]

Global biodiversity and the ancient carbon cycle – Rothman (2001) “Paleontological data for the diversity of marine animals and land plants are shown to correlate significantly with a concurrent measure of stable carbon isotope fractionation for approximately the last 400 million years.” [Full text]

Posted in AGW evidence, Global warming effects | 11 Comments »

When carbon dioxide didn’t affect climate

Posted by Ari Jokimäki on March 18, 2010

This article was originally published in Finnish in Ilmastotieto-blog.

In 1861 John Tyndall published his results on laboratory experiments where he showed that certain gases were able to absorb thermal radiation. Carbon dioxide was one of such gases. Based on that Tyndall concluded that a change in the amount of greenhouse gases in the atmosphere would necessarily cause a climate change (Tyndall, 1861). Svante Arrhenius published his theory of the effect of greenhouse gases on the climate of the Earth in 1896. His calculations suggested that addition of carbon dioxide would have a strong effect to the temperature of the Earth (Arrhenius, 1896).

From left: John Tyndall (1820-1893), Svante Arrhenius (1859-1927), Knut Ångström (1857-1910) and Charles Greeley Abbot (1872-1973). Eventhough these gentlemen ended up disagreeing on the effect of the carbon dioxide in the atmosphere, they still were all great scientists.

However, in 1900 Knut Ångström published results from laboratory experiments (Ångström, 1900) which showed that carbon dioxide wouldn’t be very significant greenhouse gas after all. It seemed that addition of carbon dioxide didn’t have much effect to the amount of radiation going through the gas, and it also seemed that the absorption band of carbon dioxide was overlapping with the absorption band of water vapour. All this wasn’t exactly new information, however. For example Rubens & Aschkinass (1898) had already observed the overlapping of the absorption bands of carbon dioxide and water vapour and they also deduced that the atmosphere is completely opaque in the wavelength region that also included carbon dioxide. After Ångström’s study, however, it was thought that there’s much more water vapour in the atmosphere and hence it’s much more significant greenhouse gas, so it seemed that the effect of water vapour masked the possible effects from the changes of carbon dioxide concentration and therefore additional carbon dioxide wouldn’t cause more warming. This became general opinion of the issue for several decades. For example, Charles Greeley Abbot noted (Abbot, 1920):

The other two absorbents are each confined in their absorbing regions to comparatively narrow ranges of spectrum, but the ozone absorption band, at about 10 microns, occurs in a region where water vapor absorbs scarcely anything while the carbon dioxide absorption band at about 14 microns occurs in a region where water vapor is also powerfully absorbing. The atmospheric proportion of carbon dioxide is sensibly constant, while water vapor and ozone are variable. Accordingly, while water vapor is certainly the most important of the three, probably ozone, although much less plentiful in the atmosphere, and certainly not more powerful as an absorber for the spectrum of a perfect radiator than carbon dioxide, is yet entitled to be regarded as second in importance on account of this peculiar posture of affairs.

So, at that time ozone seemed to be more important than carbon dioxide. Abbot also said that it might be wise to monitor the ozone in the atmosphere. Here one needs to note that at that time there wasn’t good enough measurements on the atmospheric carbon dioxide yet, which caused the carbon dioxide concentration to seem constant, eventhough by that time it already was slightly increasing (this has been observed subsequently from the ice core samples containing air bubbles, which have recorded the atmospheric greenhouse gas concentrations of past times). Simpson (1929) also discussed the matter and gave three reasons why the addition of carbon dioxide is not significant factor in the atmosphere. According to him the absorption band of carbon dioxide was too narrow for it to have much significance. Second reason was above-mentioned overlapping of the absorption bands of carbon dioxide and water vapour and as a third reason he mentioned that the current amount (back then) of atmospheric carbon dioxide already absorbs its full amount of the absorption band, and the addition of carbon dioxide wouldn’t change it significantly. This has been called the saturation of the absorption band.

So there was a general opinion that addition of carbon dioxide wouldn’t have any significant effect to the thermal radiation leaving the Earth and therefore it also wouldn’t affect Earth’s temperature. However, there were some opposing voices who thought that carbon dioxide did affect the temperature. Hulburt (1931) made some calculations relating to the matter in similar manner than Arrhenius did and Hulburt gave his support to Tyndall and Arrhenius:

Calculation shows that doubling or tripling the amount of the carbon dioxide of the atmosphere increases the average sea level temperature by about 4° and 7°K, respectively; halving or reducing to zero the carbon dioxide decreases the temperature by similar amounts. Such changes in temperature are about the same as those which occur when the earth passes from an ice age to a warm age, or vice versa. Thus the calculation indicates that the carbon dioxide theory of the ice ages, originally proposed by Tyndall, is a possible theory.

But Hulburt’s work went largely unnoticed. Also Callendar (1938) arrived to a conclusion that carbon dioxide has a heating effect. Callendar observed that the temperature of the Earth was rising, so he made a summary of old measurements of atmospheric carbon dioxide concentration and got a result that the carbon dioxide concentration of the atmosphere was rising. He also presented a calculation which suggested that carbon dioxide would have strong heating effect. Callendar’s results weren’t accepted in the scientific community. The rising carbon dioxide concentration were suspected because the measurements were inaccurate. Callendar’s calculation also had some deficiencies which was one factor in the rejection of his results. However, his work arised enough interest to cause some subsequent studies on the matter.

In the laboratories the work on the absorption properties of gases also had continued. Martin & Barker (1932) showed that the absorption bands of carbon dioxide in fact consisted of many different absorption lines, which were caused by different vibrational states of the carbon dioxide molecule. This meant that the absorption band of carbon dioxide weren’t fully saturated after all, but there were room for more absorption in between the lines.

Strong & Plass (1950) studied the effect of pressure to the thermal radiation absorption properties of the atmospheric gases. They noticed that the properties were changing with the altitude. They showed that higher in the atmosphere there is less absorption of thermal radiation than in lower parts of atmosphere. Therefore some of the radiation emitted by the lower atmosphere can escape to the space. The reason is that the absorption bands are wider in lower atmosphere than in higher atmosphere which enables the thermal radiation emitted from the edges of the absorption band by the lower atmosphere to be free to escape to the space because the narrower absorption band of the upper atmosphere doesn’t reach to the edges of the absorption band of lower atmosphere (which is also an emission band in this case). It’s like trying to block a 2 cm hole in a barrel with 1 cm plug. This is important observation for the problem discussed here. Even if the absorption band of carbon dioxide would be fully saturated in the lower parts of atmosphere, it is not saturated in higher atmosphere and the addition of carbon dioxide will cause more absorption of thermal radiation. However, Strong & Plass didn’t themselves take much stand on this issue but they concentrated more on analysing the matters relating to the stratosphere. Yet, they did say:

According to equation (18), the radiation exhausted from the atmosphere by the CO2 increases as the square root of the concentration of CO2. Since the atmosphere is at a lower temperature than the surface of the earth, the surface temperature rises as the CO2 concentration increases.

Gilbert Plass was then the person who finally solved the problem. In 1956 he published results from his study (Plass, 1956) where he had used latest laboratory measurements of the absorption properties of greenhouse gases and had determined the radiation flux in the primary absorption band of carbon dioxide in the atmosphere with a theoretical model (up to the height of 75 km). Among other things, his model included the pressure and Doppler broadening of absorption lines and the overlaps of spectral lines. According to his results, doubling of carbon dioxide concentration would cause 3.6°C warming to the surface of the Earth. In addition to this result, Plass also gave answers to all arguments that were thought to show that carbon dioxide wouldn’t cause warming to the surface of the Earth. Plass (1956b) wrote a popular article on the subject and the article happens currently to be freely accessible for everyone. In this article, there are answers to above-mentioned arguments. First the overlapping of the water vapour and carbon dioxide:

The fact that water vapor absorbs to some extent in the same spectral interval as carbon dioxide is the basis for the usual objection to the carbon dioxide theory. According to this argument the water vapor absorption is so large that there would be virtually no change in the outgoing radiation if the carbon dioxide concentration should change. However, this conclusion was based on early, very approximate treatments of the very complex problem of the calculation of the infrared flux in the atmosphere. Recent and more accurate calculations that take into account the detailed structure of the spectra of these two gases show that they are relatively independent of one another in their influence on the infrared absorption. There are two main reasons for this result: (1) there is no correlation between the frequencies of the spectral lines for carbon dioxide and water vapor and so the lines do not often overlap because of nearly coincident positions for the spectral lines; (2) the fractional concentration of water vapor falls off very rapidly with height whereas carbon dioxide is nearly uniformly distributed. Because of this last fact, even if the water vapor absorption were larger than that of carbon dioxide in a certain spectral interval at the surface of the Earth, at only a short distance above the ground the carbon dioxide absorption would be considerably larger than that of the water vapor.

And then the saturation of the carbon dioxide absorption band:

One further objection has been raised to the carbon dioxide theory: the atmosphere is completely opaque at the center of the carbon dioxide band and therefore there is no change in the absorption as the carbon dioxide amount varies. This is entirely true for a spectral interval about one micron wide on either side of the center of the carbon dioxide band. However, the argument neglects the hundreds of spectral lines from carbon dioxide that are outside this interval of complete absorption. The change in absorption for a given variation in carbon dioxide amount is greatest for a spectral interval that is only partially opaque; the temperature variation at the surface of the Earth is determined by the change in absorption of such intervals.

So the change in carbon dioxide affects the temperature because with closer inspection the absorption of carbon dioxide is not overlapping with the absorption of water vapour and water vapour is absorbing more strongly only in the lower atmosphere, and the saturation of certain parts of carbon dioxide absorption bands are already taken into consideration in the calculations which still result in the warming of the Earth’s surface when more carbon dioxide is added to the atmosphere.

This problem was solved in 1956, over 50 years ago. The solution is very straightforward and easy to understand, and it shouldn’t cause any confusion. Regardless of that, these already solved arguments are still presented in public forums as if they haven’t been solved.

Thanks for good comments to Jari, Kaitsu, and AJ.


Abbot, C. G., 1920, “The larger opportunities for research on the relations of solar and terrestrial radiation”, PNAS, 6, 82-95, [full text]

Arrhenius, Svante, 1896, “On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground.” Philosophical Magazine 41: 237-76, [full text]

Callendar, G. S., 1938, “The artificial production of carbon dioxide and its influence on temperature”, Quarterly Journal of the Royal Meteorological Society, Volume 64 Issue 275, Pages 223 – 240, [abstract]

Fleming, James R., 2002, “The carbon dioxide theory of climate change: emergence, eclipse, and reemergence, ca. 1850–1950”, 13th Symposium on Global Change and Climate Variations, AMS, [Abstract, full text]

Hulburt, E. O., 1931, “The Temperature of the Lower Atmosphere of the Earth”, Physical Review, vol. 38, Issue 10, pp. 1876-1890, [abstract]

Martin, P. E., Barker, E. F., 1932, “The Infrared Absorption Spectrum of Carbon Dioxide”, Phys. Rev. 41, 291–303, [abstract]

Plass, G. N., 1956, “The influence of the 15u carbon-dioxide band on the atmospheric infra-red cooling rate”, Quarterly Journal of the Royal Meteorological Society, Volume 82 Issue 353, Pages 310 – 324, [abstract]

Plass, Gilbert N., 1956b, “Carbon Dioxide and the Climate” – article was re-published in 2010: American Scientist, Volume 98, Number 1, Page: 58, DOI: 10.1511/2010.82.58, [full text]

Rubens, H.; Aschkinass, E., 1898, “Observations on the Absorption and Emission of Aqueous Vapor and Carbon Dioxide in the Infra-Red Spectrum”, ApJ, 8, 176, [abstract and full text]

Simpson, 1929 – information on this is from Fleming (2002), who doesn’t give any specific reference to this.

Strong, John, Plass, Gilbert N., 1950, “The Effect of Pressure Broadening of Spectral Lines on Atmospheric Temperature”, Astrophysical Journal, vol. 112, p.365, [abstract and full text]

Tyndall, John, 1861, “The Bakerian Lecture: On the Absorption and Radiation of Heat by Gases and Vapours, and on the Physical Connexion of Radiation, Absorption, and Conduction”, Proc. R. Soc. Lond. 11:100-104; doi:10.1098/rspl.1860.0021, [abstract, full text]

Weart, Spencer, 2009, “The Carbon Dioxide Greenhouse Effect”, [full text]

Ångström, Knut, 1900, “Ueber die Bedeutung des Wasserdampfes und der Kohlensäure bei der Absorption der Erdatmosphäre”, Annalen der Physik, Volume 308 Issue 12, Pages 720 – 732, [abstract (in German)]

Posted in Climate claims, Climate science | 10 Comments »

Papers on polar bear populations

Posted by Ari Jokimäki on March 15, 2010

This is a list of papers on polar bear populations. Emphasis is on climate change effect on the populations. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (July 12, 2021): Hamilton & Derocher (2018), Molnár et al. (2020), and Laidre et al. (2020) added.

UPDATE (April 12, 2018): Rode et al. (2014), Jenssen et al., Bromaghin et al. (2015), Pilfold et al. (2015), Wilson et al. (2016), Pagano et al. (2018), and Dey et al. (2017) added.
UPDATE (June 9, 2012): Stirling & Derocher (2012), Stirling & Parkinson (2006), Stirling et al. (1999), and Stirling & Derocher (1993) added.
UPDATE (October 15, 2010): Regehr et al. (2006) added. Thanks to Barry for pointing it out, see the comment section below.

Fasting season length sets temporal limits for global polar bear persistence – Molnár et al. (2020)
Abstract: Polar bears (Ursus maritimus) require sea ice for capturing seals and are expected to decline range-wide as global warming and sea-ice loss continue1,2. Estimating when different subpopulations will likely begin to decline has not been possible to date because data linking ice availability to demographic performance are unavailable for most subpopulations2 and unobtainable a priori for the projected but yet-to-be-observed low ice extremes3. Here, we establish the likely nature, timing and order of future demographic impacts by estimating the threshold numbers of days that polar bears can fast before cub recruitment and/or adult survival are impacted and decline rapidly. Intersecting these fasting impact thresholds with projected numbers of ice-free days, estimated from a large ensemble of an Earth system model4, reveals when demographic impacts will likely occur in different subpopulations across the Arctic. Our model captures demographic trends observed during 1979–2016, showing that recruitment and survival impact thresholds may already have been exceeded in some subpopulations. It also suggests that, with high greenhouse gas emissions, steeply declining reproduction and survival will jeopardize the persistence of all but a few high-Arctic subpopulations by 2100. Moderate emissions mitigation prolongs persistence but is unlikely to prevent some subpopulation extirpations within this century.
Citation: Molnár, P.K., Bitz, C.M., Holland, M.M. et al. Fasting season length sets temporal limits for global polar bear persistence. Nat. Clim. Chang. 10, 732–738 (2020).

Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation – Laidre et al. (2020)
Abstract: Kane Basin (KB) is one of the world’s most northerly polar bear (Ursus maritimus) subpopulations, where bears have historically inhabited a mix of thick multiyear and annual sea ice year-round. Currently, KB is transitioning to a seasonally ice-free region because of climate change. This ecological shift has been hypothesized to benefit polar bears in the near-term due to thinner ice with increased biological production, although this has not been demonstrated empirically. We assess sea-ice changes in KB together with changes in polar bear movements, seasonal ranges, body condition, and reproductive metrics obtained from capture–recapture (physical and genetic) and satellite telemetry studies during two study periods (1993–1997 and 2012–2016). The annual cycle of sea-ice habitat in KB shifted from a year-round ice platform (~50% coverage in summer) in the 1990s to nearly complete melt-out in summer (<5% coverage) in the 2010s. The mean duration between sea-ice retreat and advance increased from 109 to 160 days (p = .004). Between the 1990s and 2010s, adult female (AF) seasonal ranges more than doubled in spring and summer and were significantly larger in all months. Body condition scores improved for all ages and both sexes. Mean litter sizes of cubs-of-the-year (C0s) and yearlings (C1s), and the number of C1s per AF, did not change between decades. The date of spring sea-ice retreat in the previous year was positively correlated with C1 litter size, suggesting smaller litters following years with earlier sea-ice breakup. Our study provides evidence for range expansion, improved body condition, and stable reproductive performance in the KB polar bear subpopulation. These changes, together with a likely increasing subpopulation abundance, may reflect the shift from thick, multiyear ice to thinner, seasonal ice with higher biological productivity. The duration of these benefits is unknown because, under unmitigated climate change, continued sea-ice loss is expected to eventually have negative demographic and ecological effects on all polar bears.
Citation: Laidre, KLAtkinson, SNRegehr, EV, et al. Transient benefits of climate change for a high-Arctic polar bear (Ursus maritimus) subpopulation. Glob Change Biol. 2020266251– 6265

Assessment of global polar bear abundance and vulnerability – Hamilton & Derocher (2018)
Abstract: Estimates of abundance and trend are central to assessing population status; yet, are often challenging to obtain or unavailable, suffer from wide confidence intervals and may be collected at irregular intervals. Polar bears Ursus maritimus have become an iconic species for climate change, yet information on abundance and status for significant parts of their range is unknown. We examine the existing information on subpopulation abundance of polar bears across their range to assess past monitoring. We model the relationship between subpopulation densities and ecological parameters including latitude, continental shelf habitat, prey diversity, sea ice extent and the length of the ice-free season. Of the 19 subpopulations across the circumpolar Arctic, 14 have estimates (range: 161–2826 bears). Excluding three subpopulations that were regularly monitored, the mean interval between consecutive estimates was 10.9 years (range: 1–36 years), with only six subpopulations having estimates <10 years old. Subpopulation density estimates ranged from 0.57 to 9.30 bears per km2 with a mean of 2.36 bears per 1000 km2 and a median of 1.71 bears per 1000 km2. Our regression analysis found prey diversity as the only significant correlate with polar bear density. Based on this relationship, we estimate the global population at 23 315 bears (range: 15 972–31 212). An assessment of each subpopulation’s vulnerability to climate change based on subpopulation size, amount of continental shelf habitat, prey diversity and changing ice conditions indicates that the Southern Beaufort Sea, Northern Beaufort Sea and Arctic Basin subpopulations are the most vulnerable followed by the Laptev Sea and Viscount Melville Sound subpopulations. With ongoing Arctic warming and the deleterious effects of sea ice loss on polar bears, we recommend that subpopulation assessments be conducted with greater frequency and in subpopulations lacking abundance estimates such that meaningful subpopulation monitoring can proceed.
Citation: Hamilton, S.G. and Derocher, A.E. (2019), Assessment of global polar bear abundance and vulnerability. Anim Conserv, 22: 83-95.

High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear – Pagano et al. (2018) [Full text]
Abstract: Regional declines in polar bear (Ursus maritimus) populations have been attributed to changing sea ice conditions, but with limited information on the causative mechanisms. By simultaneously measuring field metabolic rates, daily activity patterns, body condition, and foraging success of polar bears moving on the spring sea ice, we found that high metabolic rates (1.6 times greater than previously assumed) coupled with low intake of fat-rich marine mammal prey resulted in an energy deficit for more than half of the bears examined. Activity and movement on the sea ice strongly influenced metabolic demands. Consequently, increases in mobility resulting from ongoing and forecasted declines in and fragmentation of sea ice are likely to increase energy demands and may be an important factor explaining observed declines in body condition and survival.
Citation: A. M. Pagano, G. M. Durner, K. D. Rode, T. C. Atwood, S. N. Atkinson, E. Peacock, D. P. Costa, M. A. Owen, T. M. Williams (2018). Science 02 Feb 2018: Vol. 359, Issue 6375, pp. 568-572. DOI: 10.1126/science.aan8677.

Increasing nest predation will be insufficient to maintain polar bear body condition in the face of sea ice loss – Dey et al. (2017) [Full text]
Abstract: Climate change can influence interspecific interactions by differentially affecting species‐specific phenology. In seasonal ice environments, there is evidence that polar bear predation of Arctic bird eggs is increasing because of earlier sea ice breakup, which forces polar bears into nearshore terrestrial environments where Arctic birds are nesting. Because polar bears can consume a large number of nests before becoming satiated, and because they can swim between island colonies, they could have dramatic influences on seabird and sea duck reproductive success. However, it is unclear whether nest foraging can provide an energetic benefit to polar bear populations, especially given the capacity of bird populations to redistribute in response to increasing predation pressure. In this study, we develop a spatially explicit agent‐based model of the predator–prey relationship between polar bears and common eiders, a common and culturally important bird species for northern peoples. Our model is composed of two types of agents (polar bear agents and common eider hen agents) whose movements and decision heuristics are based on species‐specific bioenergetic and behavioral ecological principles, and are influenced by historical and extrapolated sea ice conditions. Our model reproduces empirical findings that polar bear predation of bird nests is increasing and predicts an accelerating relationship between advancing ice breakup dates and the number of nests depredated. Despite increases in nest predation, our model predicts that polar bear body condition during the ice‐free period will continue to decline. Finally, our model predicts that common eider nests will become more dispersed and will move closer to the mainland in response to increasing predation, possibly increasing their exposure to land‐based predators and influencing the livelihood of local people that collect eider eggs and down. These results show that predator–prey interactions can have nonlinear responses to changes in climate and provides important predictions of ecological change in Arctic ecosystems.
Citation: Dey, C. J., Richardson, E. , McGeachy, D. , Iverson, S. A., Gilchrist, H. G. and Semeniuk, C. A. (2017), Increasing nest predation will be insufficient to maintain polar bear body condition in the face of sea ice loss. Glob Change Biol, 23: 1821-1831. doi:10.1111/gcb.13499.

Invariant polar bear habitat selection during a period of sea ice loss – Wilson et al. (2016) [Full text]
Abstract: Climate change is expected to alter many species’ habitat. A species’ ability to adjust to these changes is partially determined by their ability to adjust habitat selection preferences to new environmental conditions. Sea ice loss has forced polar bears (Ursus maritimus) to spend longer periods annually over less productive waters, which may be a primary driver of population declines. A negative population response to greater time spent over less productive water implies, however, that prey are not also shifting their space use in response to sea ice loss. We show that polar bear habitat selection in the Chukchi Sea has not changed between periods before and after significant sea ice loss, leading to a 75% reduction of highly selected habitat in summer. Summer was the only period with loss of highly selected habitat, supporting the contention that summer will be a critical period for polar bears as sea ice loss continues. Our results indicate that bears are either unable to shift selection patterns to reflect new prey use patterns or that there has not been a shift towards polar basin waters becoming more productive for prey. Continued sea ice loss is likely to further reduce habitat with population-level consequences for polar bears.
Citation: Ryan R. Wilson, Eric V. Regehr, Karyn D. Rode, Michelle St Martin (2016). Proc. R. Soc. B 2016 283 20160380; DOI: 10.1098/rspb.2016.0380..

Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline – Bromaghin et al. (2015) [Full text]
Abstract: We used location data from satellite-collared polar bears and environmental data (e.g., bathymetry, distance to coastlines, and sea ice) collected from 1985 to 1995 to build resource selection functions (RSFs). … We applied the RSFs to monthly maps of 21st-century sea ice concentration projected by 10 general circulation models (GCMs) used in the Intergovernmental Panel of Climate Change Fourth Assessment Report, under the A1B greenhouse gas forcing scenario. … Mean loss of optimal polar bear habitat was greatest during summer; from an observed 1.0 million km2 in 1985–1995 (baseline) to a projected multi-model mean of 0.32 million km2 in 2090–2099 (−68% change). Projected winter losses of polar bear habitat were less: from 1.7 million km2 in 1985–1995 to 1.4 million km2 in 2090–2099 (−17% change). … Although a reduction in the total amount of optimal habitat will likely reduce polar bear populations, exact relationships between habitat losses and population demographics remain unknown.
Citation: Bromaghin, J. F., McDonald, T. L., Stirling, I. , Derocher, A. E., Richardson, E. S., Regehr, E. V., Douglas, D. C., Durner, G. M., Atwood, T. and Amstrup, S. C. (2015), Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications, 25: 634-651. doi:10.1890/14-1129.1.

Multi‐temporal factors influence predation for polar bears in a changing climate – Pilfold et al. (2015) [Full text]
Abstract: Predation is an ecological interaction influenced by abiotic and biotic factors acting on multiple temporal scales, yet multi‐temporal comparisons are rare in empirical studies. For polar bears Ursus maritimus, the physical configuration of the habitat and conditions in which seals are hunted may change on intra‐ and inter‐seasonal scales. Additionally, while the effects of climate change on polar bears have focused on linking reductions in sea ice to body condition and survival, the potential changes to on‐ice hunting conditions have not been examined. Employing observational counts of seals killed by polar bears between early‐April and late‐May 1985–2011 (n = 650), we modelled the likelihood of predation events in the Beaufort Sea, Canada at multi‐temporal scales. We used the top model to estimate the expected kill rate of seals in the springs of 1985–1986 and 2005–2006 and integrated the result with fasting rates derived from physiological markers in blood samples. A log‐likelihood ratio test suggested a multi‐temporal approach fit the seal kill data better than any single scale alone. Predation events were influenced by ringed seal Pusa hispida reproduction and haul‐out behaviour, regional sea ice concentration and the phase of climatic indices. The expected kill rate from the top predation model and the estimated mean biomass of seal kills were significant predictors of polar bear fasting rates. Results suggest that 50% less seal biomass was killed in 2005–2006 than in 1985–1986, which correlates with a significant increase in the frequency of polar bears in a fasting state. We propose that the documented changes in polar bear fasting rates between 1985–1986 and 2005–2006 are due to a complex set of abiotic and biotic factors including underlying prey dynamics, rather than a single‐scale environmental correlation.
Citation: Pilfold, N. W., Derocher, A. E., Stirling, I. and Richardson, E. (2015), Multi‐temporal factors influence predation for polar bears in a changing climate. Oikos, 124: 1098-1107. doi:10.1111/oik.02000.

Anthropogenic flank attack on polar bears: interacting consequences of climate warming and pollutant exposure – Jenssen et al. (2015) [Full text]
Abstract: Polar bears (Ursus maritimus) are subjected to several anthropogenic threats, climate warming and exposure to pollutants being two of these. For polar bears, one of the main effects of climate warming is limited access to prey, due to loss of their sea ice habitat. This will result in prolonged fasting periods and emaciation and condition related negative effects on survival and reproduction success. Prolonged fasting will result in increases of the tissue concentrations of persistent organic pollutants (POPs) in polar bears, and thus increase the probability for POP levels to exceed threshold levels for effects on health, and thus on reproductive success and survival. There are clear potentials for interactions between impacts of climate warming and impacts of pollutant exposure on polar bears. It is likely that that fasting-induced increases of POPs will add to mortality rates and decrease reproductive success beyond effects caused by loss of habitat alone. However, there is a lack of studies that have addressed this. Thus, there is a need to focus on population effects of POP exposure in polar bears, and to consider such effects in relation to the effects of climate induced habitat loss.
Citation: Bjørn M. Jenssen, Gro D. Villanger, Kristin M. Gabrielsen, Jenny Bytingsvik, Thea Bechshoft, Tomasz M. Ciesielski, Christian Sonne and Rune Dietz (2015). Front. Ecol. Evol., 24 February 2015 |

Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations – Rode et al. (2014) [Full text]
Abstract: Polar bears (Ursus maritimus) have experienced substantial changes in the seasonal availability of sea ice habitat in parts of their range, including the Beaufort, Chukchi, and Bering Seas. In this study, we compared the body size, condition, and recruitment of polar bears captured in the Chukchi and Bering Seas (CS) between two periods (1986–1994 and 2008–2011) when declines in sea ice habitat occurred. In addition, we compared metrics for the CS population 2008–2011 with those of the adjacent southern Beaufort Sea (SB) population where loss in sea ice habitat has been associated with declines in body condition, size, recruitment, and survival. We evaluated how variation in body condition and recruitment were related to feeding ecology. Comparing habitat conditions between populations, there were twice as many reduced ice days over continental shelf waters per year during 2008–2011 in the SB than in the CS. CS polar bears were larger and in better condition, and appeared to have higher reproduction than SB bears. Although SB and CS bears had similar diets, twice as many bears were fasting in spring in the SB than in the CS. Between 1986–1994 and 2008–2011, body size, condition, and recruitment indices in the CS were not reduced despite a 44‐day increase in the number of reduced ice days. Bears in the CS exhibited large body size, good body condition, and high indices of recruitment compared to most other populations measured to date. Higher biological productivity and prey availability in the CS relative to the SB, and a shorter recent history of reduced sea ice habitat, may explain the maintenance of condition and recruitment of CS bears. Geographic differences in the response of polar bears to climate change are relevant to range‐wide forecasts for this and other ice‐dependent species.
Citation: Rode, K. D., Regehr, E. V., Douglas, D. C., Durner, G. , Derocher, A. E., Thiemann, G. W. and Budge, S. M. (2014), Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Glob Change Biol, 20: 76-88. doi:10.1111/gcb.12339.

Effects of Climate Warming on Polar Bears: A Review of the Evidence – Stirling & Derocher (2012) “Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze-up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long-term survival. To maintain viable subpopulations, polar bears depend upon sea ice as a platform from which to hunt seals for long enough each year to accumulate sufficient energy (fat) to survive periods when seals are unavailable. Less time to access to prey, because of progressively earlier breakup in spring, when newly-weaned ringed seal (Pusa hispida) young are available, results in longer periods of fasting, lower body condition, decreased access to denning areas, fewer and smaller cubs, lower survival of cubs as well as bears of other age classes and, finally, subpopulation decline toward eventual extirpation. The chronology of climate-driven changes will vary between subpopulations, with quantifiable negative effects being documented first in the more southerly subpopulations, such as those in Hudson Bay or the southern Beaufort Sea. As the bears’ body condition declines, more seek alternate food resources so the frequency of conflicts between bears and humans increases. In the most northerly areas, thick multiyear ice, through which little light penetrates to stimulate biological growth on the underside, will be replaced by annual ice which facilitates greater productivity and may create habitat more favorable to polar bears over continental shelf areas in the short term. If the climate continues to warm and eliminate sea ice as predicted, polar bears will largely disappear from the southern portions of their range by mid-century. They may persist in the northern Canadian Arctic Islands and northern Greenland for the foreseeable future, but their long-term viability, with a much reduced global population size in a remnant of their former range, is uncertain.” Ian Stirling, Andrew E. Derocher, Global Change Biology, DOI: 10.1111/j.1365-2486.2012.02753.x.

Predicting 21st-century polar bear habitat distribution from global climate models – Durner et al. (2009) “We used location data from satellite-collared polar bears and environmental data (e.g., bathymetry, distance to coastlines, and sea ice) collected from 1985 to 1995 to build resource selection functions (RSFs). … We applied the RSFs to monthly maps of 21st-century sea ice concentration projected by 10 general circulation models (GCMs) used in the Intergovernmental Panel of Climate Change Fourth Assessment Report, under the A1B greenhouse gas forcing scenario. … Mean loss of optimal polar bear habitat was greatest during summer; from an observed 1.0 million km2 in 1985–1995 (baseline) to a projected multi-model mean of 0.32 million km2 in 2090–2099 (−68% change). Projected winter losses of polar bear habitat were less: from 1.7 million km2 in 1985–1995 to 1.4 million km2 in 2090–2099 (−17% change). … Although a reduction in the total amount of optimal habitat will likely reduce polar bear populations, exact relationships between habitat losses and population demographics remain unknown.” [Full text]

Rebuttal of “Polar Bear Population Forecasts: A Public-Policy Forecasting Audit” – Amstrup et al. (2009) “In summary, we show that the AGS audit offers no valid criticism of the USGS conclusion that global warming poses a serious threat to the future welfare of polar bears and that it only serves to distract from reasoned public-policy debate.” [Full text]

Effects of climate change on polar bears – Wiig et al. (2008) A review article. “In this article, we review the effects on polar bears of global warming that have already been observed, and try to evaluate what may happen to the polar bears in the future. Many researchers have predicted a wide range of impacts of climate change on polar bear demography and conditions. A predicted major reduction in sea ice habitat will reduce the availability of ice associated seals, the main prey of polar bears, and a loss and fragmentation of polar bear habitat will ultimately lead to large future reductions in most subpopulations. It is likely that polar bears will be lost from many areas where they are common today and also that the total population will change into a few more distinctly isolated populations.”

Effects of Earlier Sea Ice Breakup on Survival and Population Size of Polar Bears in Western Hudson Bay – Regehr et al. (2007) “We used a flexible extension of Cormack–Jolly–Seber capture–recapture models to estimate population size and survival for polar bears (Ursus maritimus), one of the most ice-dependent of Arctic marine mammals. We analyzed data for polar bears captured from 1984 to 2004 along the western coast of Hudson Bay and in the community of Churchill, Manitoba, Canada. The Western Hudson Bay polar bear population declined from 1,194 (95% CI = 1,020–1,368) in 1987 to 935 (95% CI = 794–1,076) in 2004. … Survival of juvenile, subadult, and senescent-adult polar bears was correlated with spring sea ice breakup date, which was variable among years and occurred approximately 3 weeks earlier in 2004 than in 1984. We propose that this correlation provides evidence for a causal association between earlier sea ice breakup (due to climatic warming) and decreased polar bear survival.”

Polar Bear Population Status in the Southern Beaufort Sea – Regehr et al. (2006) An U.S. Geological Survey report. “Polar bears depend entirely on sea ice for survival. In recent years, a warming climate has caused major changes in the Arctic sea ice environment, leading to concerns regarding the status of polar bear populations. Here we present findings from long-term studies of polar bears in the southern Beaufort Sea (SBS) region of the U.S. and Canada, which are relevant to these concerns. We applied open population capture-recapture models to data collected from 2001 to 2006, and estimated there were 1,526 (95% CI = 1,211; 1,841) polar bears in the SBS region in 2006. The number of polar bears in this region was previously estimated to be approximately 1,800. Because precision of earlier estimates was low, our current estimate of population size and the earlier ones cannot be statistically differentiated. For the 2001–06 period, the best fitting capture-recapture model provided estimates of total apparent survival of 0.43 for cubs of the year (COYs), and 0.92 for all polar bears older than COYs. Because the survival rates for older polar bears included multiple sex and age strata, they could not be compared to previous estimates. Survival rates for COYs, however, were significantly lower than estimates derived in earlier studies (P = 0.03). The lower survival of COYs was corroborated by a comparison of the number of COYs per adult female for periods before (1967–89) and after (1990–2006) the winter of 1989–90, when warming temperatures and altered atmospheric circulation caused an abrupt change in sea ice conditions in the Arctic basin. In the latter period, there were significantly more COYs per adult female in the spring (P = 0.02), and significantly fewer COYs per adult female in the autumn (P < 0.001). Apparently, cub production was higher in the latter period, but fewer cubs survived beyond the first 6 months of life. Parallel with declining survival, skull measurements suggested that COYs captured from 1990 to 2006 were smaller than those captured before 1990. Similarly, both skull measurements and body weights suggested that adult males captured from 1990 to 2006 were smaller than those captured before 1990. The smaller stature of males was especially notable because it corresponded with a higher mean age of adult males. Male polar bears continue to grow into their teens, and if adequately nourished, the older males captured in the latter period should have been larger than those captured earlier. In western Hudson Bay, Canada, a significant decline in population size was preceded by observed declines in cub survival and physical stature. The evidence of declining recruitment and body size reported here, therefore, suggests vigilance regarding the future of polar bears in the SBS region.” [Full text]

Possible Effects of Climate Warming on Selected Populations of Polar Bears (Ursus maritimus) in the Canadian Arctic – Stirling & Parkinson (2006) “Polar bears depend on sea ice for survival. Climate warming in the Arctic has caused significant declines in total cover and thickness of sea ice in the polar basin and progressively earlier breakup in some areas. Inuit hunters in the areas of four polar bear populations in the eastern Canadian Arctic (including Western Hudson Bay) have reported seeing more bears near settlements during the open-water period in recent years. In a fifth ecologically similar population, no changes have yet been reported by Inuit hunters. These observations, interpreted as evidence of increasing population size, have resulted in increases in hunting quotas. However, long-term data on the population size and body condition of polar bears in Western Hudson Bay, as well as population and harvest data from Baffin Bay, make it clear that those two populations at least are more likely to be declining, not increasing. While the ecological details vary in the regions occupied by the five different populations discussed in this paper, analysis of passive-microwave satellite imagery beginning in the late 1970s indicates that the sea ice is breaking up at progressively earlier dates, so that bears must fast for longer periods during the open-water season. Thus, at least part of the explanation for the appearance of more bears near coastal communities and hunting camps is likely that they are searching for alternative food sources in years when their stored body fat depots may be depleted before freeze-up, when they can return to the sea ice to hunt seals again. We hypothesize that, if the climate continues to warm as projected by the Intergovernmental Panel on Climate Change (IPCC), then polar bears in all five populations discussed in this paper will be increasingly food-stressed, and their numbers are likely to decline eventually, probably significantly so. As these populations decline, problem interactions between bears and humans will likely continue, and possibly increase, as the bears seek alternative food sources. Taken together, the data reported in this paper suggest that a precautionary approach be taken to the harvesting of polar bears and that the potential effects of climate warming be incorporated into planning for the management and conservation of this species throughout the Arctic.” Ian Stirling and Claire L. Parkinson, Arctic, Vol. 59, No. 3 (Sep., 2006), pp. 261-275 [Full text]

Observations of mortality associated with extended open-water swimming by polar bears in the Alaskan Beaufort Sea – Monnett & Gleason (2006) “We speculate that mortalities due to offshore swimming during late-ice (or mild ice) years may be an important and unaccounted source of natural mortality given energetic demands placed on individual bears engaged in long-distance swimming. We further suggest that drowning-related deaths of polar bears may increase in the future if the observed trend of regression of pack ice and/or longer open water periods continues.” [Full text]

The influence of climate variability on polar bear (Ursus maritimus) and ringed seal (Pusa hispida) population dynamics – Rosing-Asvid (2006) “Unusually high polar bear (Ursus maritimus Phipps, 1774) predation on ringed seal (Pusa hispida (Schreber, 1775)) pups and increased survival of polar bear cubs during mild springs is documented in published articles. Strong predation on newborn ringed seal pups in early spring, however, is likely to lower the overall energy intake of polar bears if ringed seal pups are their main food, because the energetic value of ringed seal pups increases 7–8 times during the 6 week lactation period. So although hunting success in early spring increases cub survival during the period after den emergence,when they are most vulnerable, it is likely to increase the number of starving bears later in the season.” [Full text]

Population ecology of polar bears at Svalbard, Norway – Derocher (2005) “The population ecology of polar bears at Svalbard, Norway, was examined from 1988 to 2002 using live-captured animals. … However, the variation in reproduction and body mass in the population show a relationship between large-scale climatic variation and the upper trophic level in an Arctic marine ecosystem. Similar change in other polar bear populations has been attributed to climate change, and further research is needed to establish linkages between climate and the population ecology of polar bears.” [Full text]

Polar Bears in a Warming Climate – Derocher et al. (2004) “Polar bears (Ursus maritimus) live throughout the ice-covered waters of the circumpolar Arctic, particularly in near shore annual ice over the continental shelf where biological productivity is highest. However, to a large degree under scenarios predicted by climate change models, these preferred sea ice habitats will be substantially altered. … In the short term, climatic warming may improve bear and seal habitats in higher latitudes over continental shelves if currently thick multiyear ice is replaced by annual ice with more leads, making it more suitable for seals. … The effects of climate change are likely to show large geographic, temporal and even individual differences and be highly variable, making it difficult to develop adequate monitoring and research programs. All ursids show behavioural plasticity but given the rapid pace of ecological change in the Arctic, the long generation time, and the highly specialised nature of polar bears, it is unlikely that polar bears will survive as a species if the sea ice disappears completely as has been predicted by some.” [Full text]

Polar Bear Distribution and Abundance on the Southwestern Hudson Bay Coast During Open Water Season, in Relation to Population Trends and Annual Ice Patterns – Stirling et al. (2004) “We concluded that 1) the coastal survey data reliably indicated the population trends in Manitoba and Ontario; 2) little exchange occurred between the Western Hudson Bay (Manitoba) and Southern Hudson Bay (Ontario) populations; 3) between 1971 and 2001, there was a statistically significant trend toward earlier breakup of sea ice off the Manitoba coast, but not off the Ontario coast; 4) the onset of ice absence along the coast had no significant relationship to the number of bears present in each sub-sampling area within either the Manitoba or the Ontario population, but did significantly influence the distribution of bears on the coastline of each province independently of the other; 5) timing of the surveys can influence the results; and 6) adult male and female bears both showed a high degree of fidelity to specific areas during summer, independent of the pattern of ice breakup.” [Full text]

Polar Bears and Seals in the Eastern Beaufort Sea and Amundsen Gulf: A Synthesis of Population Trends and Ecological Relationships over Three Decades – Stirling (2002) “The changes in the sea ice environment, and their consequent effects on polar bears, are demonstrable in parallel fluctuations in the mean ages of polar bears killed each year by Inuit hunters. In 1989, the decadal-scale pattern in fluctuations of ice conditions in the eastern Beaufort Sea changed in response to oceanographic and climatic factors, and this change has resulted in greater amounts of open water in recent years. In addition, climatic warming will be a major environmental factor if greenhouse gas emissions continue to increase. It is unknown whether the ecosystem will return to the pattern of decadal-scale change exhibited in previous decades, or how polar bears and seals will respond to ecological changes in the future, but research on these topics is a high priority.” [Full text]

Long-Term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change – Stirling et al. (1999) “From 1981 through 1998, the condition of adult male and female polar bears has declined significantly in western Hudson Bay, as have natality and the proportion of yearling cubs caught during the open water period that were independent at the time of capture. Over this same period, the breakup of the sea ice on western Hudson Bay has been occurring earlier. There was a significant positive relationship between the time of breakup and the condition of adult females (i.e., the earlier the breakup, the poorer the condition of the bears). The trend toward earlier breakup was also correlated with rising spring air temperatures over the study area from 1950 to 1990. We suggest that the proximate cause of the decline in physical and reproductive parameters of polar bears in western Hudson Bay over the last 19 years has been a trend toward earlier breakup, which has caused the bears to come ashore in progressively poorer condition. The ultimate factor responsible for the earlier breakup in western Hudson Bay appears to be a long-term warming trend in April-June atmospheric temperatures.” Ian Stirling, Nicholas J. Lunn and John Iacozza, Arctic, Vol. 52, No. 3 (Sep., 1999), pp. 294-306.

Possible Impacts of Climatic Warming on Polar Bears – Stirling & Derocher (1993) “If climatic warming occurs, the first impacts on polar bears (Ursus maritimus) will be felt at the southern limits of their distribution, such as in James and Hudson bays, where the whole population is already forced to fast for approximately four months when the sea ice melts during the summer. Prolonging the ice-free period will increase nutritional stress on this population until they are no longer able to store enough fat to survive the ice-free period. Early signs of impact will include declining body condition, lowered reproductive rates, reduced survival of cubs, and an increase in polar bear-human interactions. Although most of these changes are currently detectable in the polar bears of western Hudson Bay, it cannot yet be determined if climatic change is involved. In the High Arctic, a decrease in ice cover may stimulate an initial increase in biological productivity. Eventually however, it is likely that seal populations will decline wherever the quality and availability of breeding habitat are reduced. Rain during the late winter may cause polar bear maternity dens to collapse, causing the death of occupants. Human-bear problems will increase as the open water period becomes longer and bears fasting and relying on their fat reserves become food stressed. If populations of polar bears decline, harvest quotas for native people will be reduced and eventually eliminated. Tourism based on viewing polar bears would become extirpated from at least the southern part of their range. If climatic warming occurs, the polar bear is an ideal species through which to monitor the cumulative effects in arctic marine ecosystems because of its position at the top of the arctic marine food chain.” Ian Stirling and Andrew E. Derocher, Arctic, Vol. 46, No. 3 (Sep., 1993), pp. 240-245. [Full text]

Posted in Climate claims, Global warming effects | 5 Comments »

Simple observational proof of greenhouse effect

Posted by Ari Jokimäki on March 10, 2010

I have seen people claiming that warmer world and more carbon dioxide is better because who wouldn’t like warmth and carbon dioxide is such a life gas (despite of the science).

I have seen people claiming that climate sensitivity is lower than thought so even if carbon dioxide has caused some warming, it won’t cause catastrophic warming (despite of the science).

I have seen people claiming that it’s not carbon dioxide that is causing warming so any actions on carbon dioxide emissions are useless (despite of the science).

I have seen people claiming that there has actually been no global warming at all but it’s just UHI and Hansen & Jones doing tricks on the temperature records (despite of the science).

I even have seen people claiming that the greenhouse effect does not exist…

The last one of these claims is why I’m writing this thing now.

The observations

Ellingson & Wiscombe (1996) gave a description of the Spectral Radiance Experiment (SPECTRE) and some initial results of the measurements. SPECTRE is a surface-based experimental field program which has a goal to “…establish a reference standard against which to compare models and also to drastically reduce the uncertainties in humidity, aerosol, etc., which radiation modelers had invoked in the past to excuse disagreements with observations.”

They are measuring the atmospheric longwave emission, i.e. the thermal radiation that atmosphere emits and which then arrives to the Earth’s surface. More specifically, they are measuring the spectrum of that emission. This is where it gets interesting. From the spectrum of thermal radiation it is possible to detect the influences of different greenhouse gases. If carbon dioxide sends thermal radiation, it has certain frequencies characteristic to carbon dioxide and as spectrum shows the emission strength at different frequencies, the spectrum shows directly if carbon dioxide is emitting thermal radiation.

In the greenhouse effect, the sunlight warms the surface of the Earth and then warm surface emits thermal radiation to the space. In atmosphere, however, there are greenhouse gases which absorb some of the emitted thermal radiation at certain frequencies (spectral bands) and then send some of it back at same spectral bands to the surface of the Earth. So, if there is a greenhouse effect caused by carbon dioxide, we should see atmosphere emitting thermal radiation at carbon dioxide’s spectral bands.

Ellingson & Wiscombe (1996) show examples of the measurements they have made. One of them is presented in Figure 1 (Fig. 3 of Ellingson & Wiscombe, 1996). There we can see at which frequencies atmosphere is emitting thermal radiation to the surface of the Earth. The effects of different greenhouse gases have been marked (CO2 is carbon dioxide, H2O is water vapor, O3 is ozone, CH4 is methane, N2O is nitrous oxide).

Figure 1. The figure 3 of Ellingson & Wiscombe (1996) showing one of their measurements of downward longwave radiation coming from atmosphere to the surface of the Earth. Measurements were made in Wisconsin, December 1991.


All we need to do is to take a peek at the Fig. 1 to see if greenhouse effect exists or not. See the effects of different greenhouse gases there? That’s the greenhouse effect.


Ellingson & Wiscombe (1996), Bulletin of the American Meteorological Society, Volume 77, Issue 9, “The Spectral Radiance Experiment (SPECTRE): Project Description and Sample Results”, [abstract, full article]

Posted in Climate claims, Climate science | 15 Comments »

Papers on ice-albedo feedback

Posted by Ari Jokimäki on March 9, 2010

This is a list of papers on ice-albedo feedback. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

UPDATE (October 23, 2010): Flanner et al. (2011) added. Thanks to Barry for pointing it out (see the discussion section).
UPDATE (October 23, 2010): Meehl & Washington (1990) added.

Radiative forcing and albedo feedback from the Northern Hemisphere cryosphere between 1979 and 2008 – Flanner et al. (2011) “The extent of snow cover and sea ice in the Northern Hemispherehas declined since 1979, coincident with hemispheric warming and indicative of a positive feedback of surface reflectivity on climate. This albedo feedback of snow on land has been quantified from observations at seasonal timescales, and century-scale feedback has been assessed using climate models. However, the total impact of the cryosphere on radiative forcing and albedo feedback has yet to be determined from measurements. Here we assess the influence of the Northern Hemisphere cryosphere on Earth’s radiation budget at the top of the atmosphere—termed cryosphere radiative forcing—by synthesizing a variety of remote sensing and field measurements. We estimate mean Northern Hemisphere forcing at −4.6 to −2.2 W m−2, with a peak in May of −9.0±2.7 W m−2. We find that cyrospheric cooling declined by 0.45 W m−2 from 1979 to 2008, with nearly equal contributions from changes in land snow cover and sea ice. On the basis of these observations, we conclude that the albedo feedback from the Northern Hemisphere cryosphere falls between 0.3 and 1.1 W m−2 K−1, substantially larger than comparable estimates obtained from 18 climate models.” M. G. Flanner, K. M. Shell, M. Barlage, D. K. Perovich & M. A. Tschudi, Nature Geoscience 4,151–155(2011)doi:10.1038/ngeo1062. [Full text]

The Global Radiative Impact of the Sea-Ice-Albedo Feedback in the Arctic – Hudson (2009) “In this study I present calculations of the global radiative impact of the reduction in Earth’s albedo resulting from reduced sea-ice cover in the Arctic. The intended result is a number, in W m-2, that represents the total increase in absorbed solar radiation due to the reduction in Arctic sea-ice cover, averaged over the globe and over the year. … Rather than try to determine this forcing with a model, in which the assumptions and approximations are difficult to see and understand, I use representative datasets and calculate the effect with relatively simple math. … The details of the calculation, including assumptions and approximations will be presented, along with a range of results for current and future changes, as well as for an estimate on the upper bound: a global-annual mean of about 0.7 W m-2.”

Sea Ice-Albedo Climate Feedback Mechanism – Curry et al. (1995) “The sea ice-albedo feedback mechanism over the Arctic Ocean multiyear sea ice is investigated by conducting a series of experiments using several one-dimensional models of the coupled sea ice-atmosphere system. In its simplest form, ice-albedo feedback is thought to be associated with a decrease in the areal cover of snow and ice and a corresponding increase in the surface temperature, further decreasing the areal cover of snow and ice. It is shown that the sea ice-albedo feedback can operate even in multiyear pack ice, without the disappearance of this ice, associated with internal processes occurring within the multiyear ice pack (e.g., duration of the snow cover, ice thickness, ice distribution, lead fraction, and melt pond characteristics). … The inclusion of melt ponds significantly strengthens the ice-albedo feedback, while the ice thickness distribution decreases the strength of the modeled sea ice-albedo feedback. It is emphasized that accurately modeling present-day sea ice thickness is not adequate for a sea ice parameterization; the correct physical processes must be included so that the sea ice parameterization yields correct sensitivities to external forcing.” [Full text]

CO2 climate sensitivity and snow-sea-ice albedo parameterization in an atmospheric GCM coupled to a mixed-layer ocean model – Meehl & Washington (1990) “The snow-sea-ice albedo parameterization in an atmospheric general circulation model (GCM), coupled to a simple mixed-layer ocean and run with an annual cycle of solar forcing, is altered from a version of the same model described by Washington and Meehl (1984). The model with the revised formulation is run to equilibrium for 1 × CO2 and 2 × CO2 experiments. The 1 ×CO2 (control) simulation produces a global mean climate about 1° warmer than the original version, and sea-ice extent is reduced. The model with the altered parameterization displays heightened sensitivity in the global means, but the geographical patterns of climate change due to increased carbon dioxide (CO2) are qualitatively similar. The magnitude of the climate change is affected, not only in areas directly influenced by snow and ice changes but also in other regions of the globe, including the tropics where sea-surface temperature, evaporation, and precipitation over the oceans are greater. With the less-sensitive formulation, the global mean surface air temperature increase is 3.5 °C, and the increase of global mean precipitation is 7.12%. The revised formulation produces a globally averaged surface air temperature increase of 4.04 °C and a precipitation increase of 7.25%, as well as greater warming of the upper tropical troposphere. Sensitivity of surface hydrology is qualitatively similar between the two cases with the larger-magnitude changes in the revised snow and ice-albedo scheme experiment. Variability of surface air temperature in the model is comparable to observations in most areas except at high latitudes during winter. In those regions, temporal variation of the sea-ice margin and fluctuations of snow cover dependent on the snow-ice-albedo formulation contribute to larger-than-observed temperature variability. This study highlights an uncertainty associated with results from current climate GCMs that use highly parameterized snow-sea-ice albedo schemes with simple mixed-layer ocean models.” Gerald A. Meehl and Warren M. Washington, Climatic Change, 1990, Volume 16, Number 3, 283-306, DOI: 10.1007/BF00144505.

Ice-albedo feedback in a CO2-doubling simulation – Dickinson et al. (1987) “We estimate the feedback of sea-ice change to the warming from CO2-doubling according to the simulation of Washington and Meehl (1984). Without ice-snow albedo feedback, their global warming of 3.5 °C would have been 2.2. °C according to our estimate of the ice-snow feedback. About 80% of the albedo change from ice and snow occurred in the Southern Hemisphere.”

Effect of Ice-Albedo Feedback on Global Sensitivity in a One-Dimensional Radiative-Convective Climate Model – Wang & Stone (1980) “The feedback between ice albedo and temperature is included in a one-dimensional radiative-convective climate model. The effect of this feedback on global sensitivity to changes in solar constant is studied for the current climate conditions. This ice-albedo feedback amplifies global sensitivity by 26 and 39%, respectively, for assumptions of fixed cloud altitude and fixed cloud temperature. The global sensitivity is not affected significantly if the latitudinal variations of mean solar zenith angle and cloud cover are included in the global model.” [Full text]

Energy Balance Climate Models: A Reappraisal of Ice-Albedo Feedback – Lian & Cess (1977) “Disagreement exists, with regard to different types of climate models, concerning the influence of ice-albedo feedback upon the stability of the present global climate. In view of this we have reexamined the empirical relationship between zonal albedo and temperature for use in zonally averaged energy-balance climate models, and conclude that ice-albedo feedback constitutes a relatively mild climate feedback mechanism, amplifying global climate sensitivity by roughly 25%.” [Full text]

Regional effects

Sea Ice-Albedo Feedback and Nonlinear Arctic Climate Change – Winton (2008) “The potential for sea ice―albedo feedback to give rise to nonlinear climate change in the Arctic Ocean region, defined as a nonlinear relationship between polar and global temperature change or, equivalently, a time-varying polar amplification, is explored in the Intergovernmental Panel on Climate Change climate models. Five models supplying Special Report on Emissions Scenario A1B ensembles for the 21st century are examined, and very linear relationships are found between polar and global temperatures (indicating linear polar region climate change) and between polar temperature and albedo (the potential source of nonlinearity). … Atmospheric heat transport exerts a strong cooling effect during the transition to annually ice-free conditions, counteracting the albedo change. Specialized experiments with atmosphere-only and coupled models show that the main damping mechanism for sea ice region surface temperature is reduced upward heat flux through the adjacent ice-free oceans resulting in reduced atmospheric heat transport into the region.” [Full text]

Impact of ice-albedo feedback on hemispheric scale sea-ice melting rates in the Antarctic using Multi-frequency Scanning Microwave Radiometer data – Mitra et al. (2008) “In this study the Multi-frequency Scanning Microwave Radiometer (MSMR) brightness temperature data over the Antarctic/Southern Ocean region is used to calculate the weekly sea-ice extents, during the melting phase from August 1999 to March 2000 to quantitatively estimate the melting rates of sea-ice on a hemispheric scale. … The observed melting rate behaviour indicates that apart from the seasonal cycle of solar irradiance, it is controlled by other mechanisms like the icealbedo feedback. The present study estimates the feedback factor, response time and acceleration in the melting rate, which are important towards a better quantitative understanding of the future of Antarctic sea-ice variability, and the climate trends in the context of global warming.”

What drove the dramatic retreat of arctic sea ice during summer 2007? – Zhang et al. (2008) “A model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007. It is found that preconditioning, anomalous winds, and ice-albedo feedback are mainly responsible for the retreat.” [Full text]

Increasing solar heating of the Arctic Ocean and adjacent seas, 1979–2005: Attribution and role in the ice-albedo feedback – Perovich et al. (2007) “This study addresses how the amount of solar energy absorbed in areas of open water in the Arctic Basin has varied spatially and temporally over the past few decades. A synthetic approach was taken, combining satellite-derived ice concentrations, incident irradiances determined from reanalysis products, and field observations of ocean albedo over the Arctic Ocean and the adjacent seas. Results indicate an increase in the solar energy deposited in the upper ocean over the past few decades in 89% of the region studied. The largest increases in total yearly solar heat input, as much as 4% per year, occurred in the Chukchi Sea and adjacent areas.” [Full text]

Lake Superior summer water temperatures are increasing more rapidly than regional air temperatures: A positive ice-albedo feedback – Austin & Colman (2007) “Lake Superior summer (July–September) surface water temperatures have increased approximately 2.5°C over the interval 1979–2006, equivalent to a rate of (11 ± 6) × 10−2°C yr−1, significantly in excess of regional atmospheric warming. This discrepancy is caused by declining winter ice cover, which is causing the onset of the positively stratified season to occur earlier at a rate of roughly a half day per year. An earlier start of the stratified season significantly increases the period over which the lake warms during the summer months, leading to a stronger trend in mean summer temperatures than would be expected from changes in summer air temperature alone.” [Full text]

Observational evidence of a hemispheric-wide ice–ocean albedo feedback effect on Antarctic sea-ice decay – Nihashi & Cavalieri (2006) “The effect of ice–ocean albedo feedback (a kind of ice-albedo feedback) on sea-ice decay is demonstrated over the Antarctic sea-ice zone from an analysis of satellite-derived hemispheric sea ice concentration and European Centre for Medium-Range Weather Forecasts (ERA-40) atmospheric data for the period 1979–2001. Sea ice concentration in December (time of most active melt) correlates better with the meridional component of the wind-forced ice drift (MID) in November (beginning of the melt season) than the MID in December. This 1 month lagged correlation is observed in most of the Antarctic sea-ice covered ocean. Daily time series of ice concentration show that the ice concentration anomaly increases toward the time of maximum sea-ice melt. These findings can be explained by the following positive feedback effect: once ice concentration decreases (increases) at the beginning of the melt season, solar heating of the upper ocean through the increased (decreased) open water fraction is enhanced (reduced), leading to (suppressing) a further decrease in ice concentration by the oceanic heat. Results obtained from a simple ice–ocean coupled model also support our interpretation of the observational results. This positive feedback mechanism explains in part the large interannual variability of the sea-ice cover in summer.”

Amplified Arctic climate change: What does surface albedo feedback have to do with it? – Winton (2006) “Forcings and feedbacks that impact the warming response are estimated for both Arctic and global regions based on standard model diagnostics. … SAF [surface albedo feedback] is shown to be a contributing, but not a dominating, factor in the simulated Arctic amplification and its intermodel variation.” [Full text]

Hydraulic controls of summer Arctic pack ice albedo – Eicken et al. (2004) “Linkages between albedo, surface morphology, melt pond distribution, and properties of first-year and multiyear sea ice have been studied at two field sites in the North American Arctic between 1998 and 2001. It is shown that summer sea-ice albedo depends critically on surface melt-pond hydrology, controlled by melt rate, ice permeability, and topography. Remarkable short-term and interannual variability in pond fraction varying by more than a factor of 2 and hence area-averaged albedo (varying between 0.28 and 0.49 over the period of a few days) were observed to be forced by millimeter to centimeter changes in pond water level. … Our work indicates that ice-albedo prediction in large-scale models with conventional methods is inherently difficult, if not impossible. However, a hydrological model, incorporating measured statistics of ice topography, reproduces observed pond features and variability, pointing toward an alternative approach in predicting ice albedo in numerical simulations.” [Full text]

Seasonal evolution of the albedo of multiyear Arctic sea ice – Perovich et al. (2002) “As part of ice albedo feedback studies during the Surface Heat Budget of the Arctic Ocean (SHEBA) field experiment, we measured spectral and wavelength-integrated albedo on multiyear sea ice. Measurements were made every 2.5 m along a 200-m survey line from April through October. Initially, this line was completely snow covered, but as the melt season progressed, it became a mixture of bare ice and melt ponds. Observed changes in albedo were a combination of a gradual evolution due to seasonal transitions and abrupt shifts resulting from synoptic weather events. There were five distinct phases in the evolution of albedo: dry snow, melting snow, pond formation, pond evolution, and fall freeze-up. In April the surface albedo was high (0.8–0.9) and spatially uniform. By the end of July the average albedo along the line was 0.4, and there was significant spatial variability, with values ranging from 0.1 for deep, dark ponds to 0.65 for bare, white ice.”

Applications of SHEBA/FIRE data to evaluation of snow/ice albedo parameterizations – Curry et al. (2001) “Climate models use a wide variety of parameterizations for surface albedos of the ice-covered ocean. … Observations obtained in the Arctic Ocean during 1997–1998 in conjunction with the Surface Heat Budget of the Arctic Ocean (SHEBA) and FIRE Arctic Clouds Experiment provide a unique data set against which to evaluate parameterizations of sea ice surface albedo. … Results show that these parameterizations yield very different representations of the annual cycle of sea ice albedo. … The baseline sea ice characteristics and strength of the ice-albedo feedback are compared for the simulations of the different surface albedos.” [Full text]

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Will Watts set the record straight and apologize?

Posted by Ari Jokimäki on March 6, 2010

For a while now Tamino has been studying the claims presented by Joseph D’Aleo and Anthony Watts:

Summer and Smoke
GHCN: preliminary results
False Claims Proven False
Interesting Comment
Show and Tell
Replication, not repetition
Global Update

Tamino has done great work here showing without a doubt that D’Aleo & Watts are wrong about their claims. Here’s the latest post on the issue:

Message to Anthony Watts

Let’s take a quote from there:

If you have any honor at all, you’ll set the record straight. You owe it to everyone, and especially to NOAA, to admit that you were wrong. And you certainly owe it to NOAA to apologize. You need to make a highly visible, highly public admission of error, and apology, for using falsehoods to accuse others of fraud.

Are you man enough?

We are waiting, Mr. Watts.

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Underground temperatures as indicators of surface temperatures – part 2

Posted by Ari Jokimäki on March 3, 2010

This article was originally written and published by me in Finnish in Ilmastotieto-blog and this is just an English version of it.

Continued from part 1.

Subsurface temperature

There are two main factors affecting the subsurface temperature: the temperature changes in the surface and the heat from the Earth’s core. The heat from the Earth’s core varies very slowly over million year timescales. Surface temperature on the other hand varies in relatively short timescales. These two factors can be separated from each other because the changes in the heat from the Earth’s core are so slow. When temperature evolution is being studied in time periods of hundreds or thousands of years, the heat flux from the Earth’s core can be assumed to be constant, which enables us to separate the short time variations as changes due to surface temperature variations.

The surface temperature variations are being transferred to deeper ground as heat waves. The amplitude of the waves decreases strongly when going deeper and the decrease of amplitude depends on the frequency of the wave; fast changes decrease more quickly than slow changes. It is because of this that the annual temperature changes show deeper than daily temperature changes. Also because of that, eventhough the daily and annual changes are much bigger than the long-period climate changes, the daily and annual changes are not seen deeper than few tens of meters while the long-period climate changes are seen deeper. The surface temperature changes penetrate deep ground at such speed that the temperature changes of thousand years are typically seen in upper 500 meters.

So the steady influence of the heat from the Earth’s core must be separated from the measured temperature profile. After this a profile is left that is called the ‘‘residual’’ temperature profile. The final surface temeprature reconstruction is based on the residual temperature profile. Reconstructions have been done by two models; forward models and inverse models. In a forward model certain history is first assumed for the climate and from that it is computed how the subsurface temperature profile should look. The result is compared to the measured profile. The assumed climate history is then corrected to more suitable one and the comparison is performed again. Like that the model that fits to the measurements is sought and the output of that model is then the surface temperature reconstruction. In inverse models the surface temperature is derived directly from the observations.

When a reconstruction is made from a combination of several boreholes, many disturbing factors can be eliminated at least partly. Disturbing factors are mostly characteristic to the borehole and are not seen in many boreholes simultaneously, so the features changing simultaneously in several boreholes can be thought to describe changing climate. In addition to that, the reconstruction is usually compared to the surface temperature record measured from the region, so that it is certain that the reconstruction really shows surface temperature at least during that time when there’s data from both sources available.

The usage of subsurface temperatures is restricted by their bad resolution in time, i.e. the fact that they don’t show fast variations in same manner as for example tree-rings, which show annual variation. Good aspect is that reconstructions from subsurface temperatures represent longer time temperature averages well. There are also lot of measurements available with good geographical coverage. For example from Southern Hemisphere there are lot of reconstructions from subsurface temperatures while there are only few of other reconstructions from there. Even in Finland some reconstructions based on subsurface temperatures have been done [this note was included because the article was originally to a Finnish audience].

Global surface temperature from borehole reconstructions

Also global analyses have been made from borehole reconstructions. As in other reconstructions and in surface temperature analyses, also in global borehole reconstructions it must be solved how to combine the data from different sources in a meaningful way. There is lot of research on the subject. In addition to some global analyses presented below, for example Mann et al. (2003) ja Pollack & Smerdon (2004) are noteworthy. “Global” is here like in other reconstruction methods rather relative concept because borehole measurements made from ocean floor are not being used (ocean floor measurements are not made deep enough – they are usually only few meters deep) and the global distribution of boreholes is not evenly spread even in land boreholes.

Here are some global reconstructions and their results briefly:

Huang et al. (1997) use subsurface heat flux measurements to make a 20,000 year surface temperature reconstruction. Their results show that early and middle Holocene were warmer than present and additionally there was a warmer period than present also about 500-1000 years ago. But their most important result is probably this:

Although temperature variations in this type of reconstruction are highly smoothed, the results clearly resemble the broad outlines of late Quaternary climate changes suggested by proxies.

Pollack et al. (1998) – global analysis of 358 boreholes for the last 500 years shows that:

…in the 20th century, the average surface temperature of Earth has increased by about 0.5°C and that the 20th century has been the warmest of the past five centuries. The subsurface temperatures also indicate that Earth’s mean surface temperature has increased by about 1.0°C over the past five centuries.

Huang et al. (2000) – also for 500 years but from 616 boreholes:

The results confirm the unusual warming of the twentieth century revealed by the instrumental record, but suggest that the cumulative change over the past five centuries amounts to about 1 K, exceeding recent estimates from conventional climate proxies.

Pollack & Huang (2000) – as a review article mostly reviews the results of other works from 600 boreholes for last 500 years:

Taken as a global ensemble, the borehole data indicate a temperature increase over the past 5 centuries of about 1 K, half of which has occurred in the twentieth century alone (Figure 7). This estimate of twentieth century warming is similar in trend to the instrumental record of surface warming determined from meteorological stations (Jones et al 1999b). When this trend is added to the more gradual warming in the previous centuries, the twentieth century stands out as the warmest century of the past five, a result similar to many recent multi-proxy reconstructions (Overpeck et al 1997; Jones et al 1998; Mann et al 1998, 1999) that did not include any geothermal component.

Beltrami (2002) – 500 year global reconstruction from 826 boreholes:

Results indicate that the global average ground temperature and ground heat flux have increased an average of 0.45°K and 18.0 mWm2 respectively over the last 200 years, and 0.9°K in the last five centuries.

Huang et al. (2008) – modern version of Huang et al. (1997). This study also is from last 20,000 years and it uses subsurface heat flux measurements and subsurface temperature measurements combined with modern surface temperature record. Their reconstruction is shown in Figure 2. The results of the study are broadly similar as in their 1997 study, but the details have changed a little:

The reconstructions show the temperatures of the mid-Holocene warm episode some 1–2 K above the reference level, the maximum of the MWP at or slightly below the reference level, the minimum of the LIA about 1 K below the reference level, and end-of-20th century temperatures about 0.5 K above the reference level.

Figure 2. Reconstruction of global surface temperature anomaly from subsurface temperature and heat flux measurements combined with modern surface temperature record. Y-axis is the surface temperature anomaly in kelvins and X-axis is years in thousands of years ago. The highest point is the Holocene climate optimum (about 6000 years ago). Lowest point is the latest ice age. Other points worth mentioning are the medieval warm period (slight peak about 1000 years ago), little ice age (couple of hundred years ago) and the late 20th century (at the point zero years ago). The zero point of surface temperature anomaly is the 1961-1990 mean. The data is from NOAA Paleoclimatology website and is originally from Huang et al. (2008).

Thanks to Kaitsu, Esko and Jari for good comments on this article.


Beltrami (2002), “Beltrami, H. (2002), Climate from borehole data: Energy fluxes and temperatures since 1500, Geophys. Res. Lett., 29(23), 2111, doi:10.1029/2002GL015702, [abstract, full text]

Huang et al. (1997), “Late Quaternary temperature changes seen in world-wide continental heat flow measurements”, Geophys. Res. Lett., 24(15), 1947–1950, [abstract, full text]

Huang et al. (2000), “Temperature trends over the past five centuries reconstructed from borehole temperatures”, Nature 403, 756-758, doi:10.1038/35001556, [abstract, full text]

Huang et al. (2008), “A late Quaternary climate reconstruction based on borehole heat flux data, borehole temperature data, and the instrumental record”, Geophys. Res. Lett., 35, L13703, doi:10.1029/2008GL034187, [abstract, full text]

Mann et al. (2003), “Optimal surface temperature reconstructions using terrestrial borehole data”, J. Geophys. Res., 108(D7), 4203, doi:10.1029/2002JD002532, [abstract, full text]

Pollack et al. (1998), “Climate Change Record in Subsurface Temperatures: A Global Perspective”, Science 9 October 1998:
Vol. 282. no. 5387, pp. 279 – 281, DOI: 10.1126/science.282.5387.279, [abstract, full text]

Pollack & Huang (2000), “Climate Reconstruction from Subsurface Temperatures”, Annual Review of Earth and Planetary Sciences, Vol. 28: 339-365, doi:10.1146/, [abstract, full text]

Pollack & Smerdon (2004), “Borehole climate reconstructions: Spatial structure and hemispheric averages”, J. Geophys. Res., 109, D11106, doi:10.1029/2003JD004163, [abstract, full text]

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Comments on Spencer’s strange statements on CRUTEM3

Posted by Ari Jokimäki on March 2, 2010

I was reading this article from Open Mind the other day and I even read the comment section. There a commenter named “Robert” quoted Roy Spencer saying something about CRUTEM3 surface temperature set (the land part of the HadCRUT3 land & ocean surface temperature analysis) that really seemed strange to me. Below I’ll explain why.

The quote in question is from this Roy Spencer blog article. There Spencer first explains how he is in the process of comparing the CRUTEM3 and NOAA ISH datasets (link is to a summary page, Spencer uses more complete data set which doesn’t seem to be available for laypeople). He then shows a figure showing both datasets from 1973 to 2009 and notes:

But while the monthly variations are very similar, the warming trend in the Jones dataset is about 20% greater than the warming trend in my ISH data analysis.

The comment I found strange comes next:

This is a little curious since I have made no adjustments for increasing urban heat island (UHI) effects over time, which likely are causing a spurious warming effect, and yet the Jones dataset which IS (I believe) adjusted for UHI effects actually has somewhat greater warming than the ISH data.

So, what is there so strange about this quote?

First, Roy Spencer is a scientist so he should know how to look for information on these things and yet he just seems to proceed by guessing (as he only “believes” CRUTEM3 is adjusted for UHI). Now, how should we check if “Jones dataset” (CRUTEM3) is adjusted for UHI effects? This is the website Spencer got the data from. Would it be a good idea to look what they say about their dataset? Well, they don’t say much but they do give references to scientific research articles on their dataset. Roy Spencer as a scientist most likely has access to all of the given papers but gladly they offer the latest paper for free there, here’s the link (Brohan et al. 2006).

Second, CRUTEM3 is not adjusted for UHI effects. The UHI effect is included to the uncertainty values which doesn’t show if one only uses nominal values like Spencer does (shouldn’t a scientist consider uncertainty too when determining a difference between two datasets?). You can see the effect of UHI in Brohan et al. Fig. 10 where it is as one factor to the blue uncertainty band. (IPCC AR4 WGI also discusses this.)

There you have it: regardless of what is causing the difference in the datasets Spencer is comparing (and I see Spencer pondering much about CRUTEM3 and UHI but I don’t see him considering the ISH dataset at all – it is as if Spencer would have already decided before the analysis that there is a problem in the CRUTEM3 or in the “Jones dataset” as he calls it for some reason), my message here is that the approach presented in Spencer’s blog entry doesn’t appear very scientific and the strange part is that the Author of the blog entry is a scientist. But when I read the final conclusion (“It is increasingly apparent that we do not even know how much the world has warmed in recent decades, let alone the reason(s) why. It seems to me we are back to square one.”), the whole thing takes even more bizarre turn. Here we have what seems to be half-baked comparison of two datasets followed by what seems to be quite standard nonsense conclusions you usually see in denialist blogs. From a scientist I would expect far better than this. I cannot help wondering if there are two persons who call themselves Dr. Roy Spencer and write about climate issues.

P.S. There has been lot of research on urban heat island effects, by the way.

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