AGU Blogosphere

If you are interested in Earth sciences and tired of seeing us amateurs blogging about it, then you should see the AGU Blogosphere. It’s the real scientists blogging about the Earth science (oh, and space science too – I’m also interested in astronomy) – not only about climate science but many different fields (well, geology probably being at center of the focus as it’s American Geophysical Union). This one goes straight to my RSS-feed reader.

Papers on Greenland temperature

This is a list of papers on Greenland temperatures with an emphasis on modern temperatures. 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 (August 28, 2011): Kobashi et al. (2011), Masson-Delmotte et al. (2012), and Hall et al. (2012) added.
UPDATE (January 7, 2011): Alley & Koci (1990) added.

Greenland climate change: from the past to the future – Masson-Delmotte et al. (2012) “Climate archives available from deep sea and marine shelf sediments, glaciers, lakes, and ice cores in and around Greenland allow us to place the current trends in regional climate, ice sheet dynamics, and land surface changes in a broader perspective. We show that, during the last decade (2000s), atmospheric and sea surface temperatures are reaching levels last encountered millennia ago, when northern high latitude summer insolation was higher due to a different orbital configuration. Records from lake sediments in southern Greenland document major environmental and climatic conditions during the last 10,000 years, highlighting the role of soil dynamics in past vegetation changes, and stressing the growing anthropogenic impacts on soil erosion during the recent decades. Furthermore, past and present changes in atmospheric and oceanic heat advection appear to strongly influence both regional climate and ice sheet dynamics. Projections from climate models are investigated to quantify the magnitude and rates of future changes in Greenland temperature, which may be faster than past abrupt events occurring under interglacial conditions. Within one century, in response to increasing greenhouse gas emissions, Greenland may reach temperatures last time encountered during the last interglacial period, approximately 125,000 years ago. We review and discuss whether analogies between the last interglacial and future changes are reasonable, because of the different seasonal impacts of orbital and greenhouse gas forcings. Over several decades to centuries, future Greenland melt may act as a negative feedback, limiting regional warming albeit with global sea level and climatic impacts.” Valérie Masson-Delmotte, Didier Swingedouw, Amaëlle Landais, Marit-Solveig Seidenkrantz, Emilie Gauthier, Vincent Bichet, Charly Massa, Bianca Perren, Vincent Jomelli, Gudfinna Adalgeirsdottir, Jens Hesselbjerg Christensen, Jette Arneborg, Uma Bhatt, Donald A. Walker, Bo Elberling, Fabien Gillet-Chaulet, Catherine Ritz, Hubert Gallée, Michiel van den Broeke, Xavier Fettweis, Anne de Vernal, Bo Vinther, Wiley Interdisciplinary Reviews: Climate Change, Volume 3, Issue 5, pages 427–449, September/October 2012, DOI: 10.1002/wcc.186.

A Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet – Hall et al. (2012) “The authors have developed a climate-quality data record of the clear-sky surface temperature of the Greenland Ice Sheet using the Moderate-Resolution Imaging Spectroradiometer (MODIS) ice-surface temperature (IST) algorithm. Daily and monthly quality-controlled MODIS ISTs of the Greenland Ice Sheet beginning on 1 March 2000 and continuing through 31 December 2010 are presented at 6.25-km spatial resolution on a polar stereographic grid along with metadata to permit detailed accuracy assessment. The ultimate goal is to develop a climate data record (CDR) that starts in 1981 with the Advanced Very High Resolution Radiometer (AVHRR) Polar Pathfinder (APP) dataset and continues with MODIS data from 2000 to the present, and into the Visible Infrared Imager Radiometer Suite (VIIRS) era (the first VIIRS instrument was launched in October 2011). Differences in the APP and MODIS cloud masks have thus far precluded merging the APP and MODIS IST records, though this will be revisited after the APP dataset has been reprocessed with an improved cloud mask. IST of Greenland may be used to study temperature and melt trends and may also be used in data assimilation modeling and to calculate ice sheet mass balance. The MODIS IST climate-quality dataset provides a highly consistent and well-characterized record suitable for merging with earlier and future IST data records for climate studies. The complete MODIS IST daily and monthly data record is available online.” Hall, Dorothy K., Josefino C. Comiso, Nicolo E. DiGirolamo, Christopher A. Shuman, Jeffrey R. Key, Lora S. Koenig, 2012: A Satellite-Derived Climate-Quality Data Record of the Clear-Sky Surface Temperature of the Greenland Ice Sheet. J. Climate, 25, 4785–4798. doi: http://dx.doi.org/10.1175/JCLI-D-11-00365.1. [Full text]

High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core – Kobashi et al. (2011) “Greenland recently incurred record high temperatures and ice loss by melting, adding to concerns that anthropogenic warming is impacting the Greenland ice sheet and in turn accelerating global sea-level rise. Yet, it remains imprecisely known for Greenland how much warming is caused by increasing atmospheric greenhouse gases versus natural variability. To address this need, we reconstruct Greenland surface snow temperature variability over the past 4000 years at the GISP2 site (near the Summit of the Greenland ice sheet; hereafter referred to as Greenland temperature) with a new method that utilises argon and nitrogen isotopic ratios from occluded air bubbles. The estimated average Greenland snow temperature over the past 4000 years was −30.7°C with a standard deviation of 1.0°C and exhibited a long-term decrease of roughly 1.5°C, which is consistent with earlier studies. The current decadal average surface temperature (2001–2010) at the GISP2 site is −29.9°C. The record indicates that warmer temperatures were the norm in the earlier part of the past 4000 years, including century-long intervals nearly 1°C warmer than the present decade (2001–2010). Therefore, we conclude that the current decadal mean temperature in Greenland has not exceeded the envelope of natural variability over the past 4000 years, a period that seems to include part of the Holocene Thermal Maximum. Notwithstanding this conclusion, climate models project that if anthropogenic greenhouse gas emissions continue, the Greenland temperature would exceed the natural variability of the past 4000 years sometime before the year 2100.” Kobashi, T., K. Kawamura, J. P. Severinghaus, J.-M. Barnola, T. Nakaegawa, B. M. Vinther, S. J. Johnsen, and J. E. Box (2011), High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core, Geophys. Res. Lett., 38, L21501, doi:10.1029/2011GL049444. [Full text]

Persistent multi-decadal Greenland temperature fluctuation through the last millennium – Kobashi et al. (2010) “Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.” Takuro Kobashi, Jeffrey P. Severinghaus, Jean-Marc Barnola, Kenji Kawamura, Tara Carter and Tosiyuki Nakaegawa, Climatic Change, Volume 100, Numbers 3-4, 733-756, DOI: 10.1007/s10584-009-9689-9. [Full text]

Greenland Ice Sheet Surface Air Temperature Variability: 1840–2007 – Box et al. (2009) “Meteorological station records and regional climate model output are combined to develop a continuous 168-yr (1840–2007) spatial reconstruction of monthly, seasonal, and annual mean Greenland ice sheet near-surface air temperatures. Independent observations are used to assess and compensate for systematic errors in the model output. Uncertainty is quantified using residual nonsystematic error. Spatial and temporal temperature variability is investigated on seasonal and annual time scales. It is found that volcanic cooling episodes are concentrated in winter and along the western ice sheet slope. Interdecadal warming trends coincide with an absence of major volcanic eruptions. Year 2003 was the only year of 1840–2007 with a warm anomaly that exceeds three standard deviations from the 1951–80 base period. The annual whole ice sheet 1919–32 warming trend is 33% greater in magnitude than the 1994–2007 warming. The recent warming was, however, stronger along western Greenland in autumn and southern Greenland in winter. Spring trends marked the 1920s warming onset, while autumn leads the 1994–2007 warming. In contrast to the 1920s warming, the 1994–2007 warming has not surpassed the Northern Hemisphere anomaly. An additional 1.0°–1.5°C of annual mean warming would be needed for Greenland to be in phase with the Northern Hemispheric pattern. Thus, it is expected that the ice sheet melt rates and mass deficit will continue to grow in the early twenty-first century as Greenland’s climate catches up with the Northern Hemisphere warming trend and the Arctic climate warms according to global climate model predictions.” Box, Jason E., Lei Yang, David H. Bromwich, Le-Sheng Bai, 2009: Greenland Ice Sheet Surface Air Temperature Variability: 1840–2007*. J. Climate, 22, 4029–4049, doi: 10.1175/2009JCLI2816.1.

Greenland ice sheet surface temperature, melt and mass loss: 2000-06 – Hall et al. (2008) “A daily time series of ‘clear-sky’ surface temperature has been compiled of the Greenland ice sheet (GIS) using 1 km resolution moderate-resolution imaging spectroradiometer (MODIS) land-surface temperature (LST) maps from 2000 to 2006. We also used mass-concentration data from the Gravity Recovery and Climate Experiment (GRACE) to study mass change in relationship to surface melt from 2003 to 2006. The mean LST of the GIS increased during the study period by ∼0.27°C a−1. The increase was especially notable in the northern half of the ice sheet during the winter months. Melt-season length and timing were also studied in each of the six major drainage basins. Rapid (<15 days) and sustained mass loss below 2000 m elevation was triggered in 2004 and 2005 as recorded by GRACE when surface melt begins. Initiation of large-scale surface melt was followed rapidly by mass loss. This indicates that surface meltwater is flowing rapidly to the base of the ice sheet, causing acceleration of outlet glaciers, thus highlighting the metastability of parts of the GIS and the vulnerability of the ice sheet to air-temperature increases. If air temperatures continue to rise over Greenland, increased surface melt will play a large role in ice-sheet mass loss.” Hall, Dorothy K.; Williams, Richard S.; Luthcke, Scott B.; Digirolamo, Nicolo E., Journal of Glaciology, Volume 54, Number 184, January 2008 , pp. 81-93(13). [Full text]

Comparison of satellite-derived and in-situ observations of ice and snow surface temperatures over Greenland – Hall et al. (2008) “The most practical way to get spatially broad and continuous measurements of the surface temperature in the data-sparse cryosphere is by satellite remote sensing. The uncertainties in satellite-derived LSTs must be understood to develop internally-consistent decade-scale land surface temperature (LST) records needed for climate studies. In this work we assess satellite-derived “clear-sky” LST products from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), and LSTs derived from the Enhanced Thematic Mapper Plus (ETM+) over snow and ice on Greenland. When possible, we compare satellite-derived LSTs with in-situ air temperature observations from Greenland Climate Network (GC-Net) automatic weather stations (AWS). We find that MODIS, ASTER and ETM+ provide reliable and consistent LSTs under clear-sky conditions and relatively-flat terrain over snow and ice targets over a range of temperatures from − 40 to 0 °C. The satellite-derived LSTs agree within a relative RMS uncertainty of ~ 0.5 °C. The good agreement among the LSTs derived from the various satellite instruments is especially notable since different spectral channels and different retrieval algorithms are used to calculate LST from the raw satellite data. The AWS record in-situ data at a “point” while the satellite instruments record data over an area varying in size from: 57 × 57 m (ETM+), 90 × 90 m (ASTER), or to 1 × 1 km (MODIS). Surface topography and other factors contribute to variability of LST within a pixel, thus the AWS measurements may not be representative of the LST of the pixel. Without more information on the local spatial patterns of LST, the AWS LST cannot be considered valid ground truth for the satellite measurements, with RMS uncertainty ~ 2 °C. Despite the relatively large AWS-derived uncertainty, we find LST data are characterized by high accuracy but have uncertain absolute precision.” Dorothy K. Hall, Jason E. Box, Kimberly A. Casey, Simon J. Hook, Christopher A. Shuman and Konrad Steffen, Remote Sensing of Environment, Volume 112, Issue 10, 15 October 2008, Pages 3739-3749, doi:10.1016/j.rse.2008.05.007. [Full text]

Greenland warming of 1920–1930 and 1995–2005 – Chylek et al. (2006) “We provide an analysis of Greenland temperature records to compare the current (1995–2005) warming period with the previous (1920–1930) Greenland warming. We find that the current Greenland warming is not unprecedented in recent Greenland history. Temperature increases in the two warming periods are of a similar magnitude, however, the rate of warming in 1920–1930 was about 50% higher than that in 1995–2005.” Chylek, P., M. K. Dubey, and G. Lesins (2006), Geophys. Res. Lett., 33, L11707, doi:10.1029/2006GL026510. [Full text]

Upper-air temperatures around Greenland: 1964–2005 – Box & Cohen (2006) “A 42-year collection of 12h balloon soundings from six sites surrounding Greenland reveal distinct patterns of tropospheric and stratospheric temperature variability. Seasonal mean upper-air temperatures exhibit statistically significant correlations with surface air temperature records. Over the full 1964–2005 record, patterns of statistically significant tropospheric warming and stratospheric cooling are evident. Overall, the magnitude of warming decreases with height, becoming cooling in the mid-stratosphere. During the recent 12-year period (1994–2005) lacking major volcanic forcing, statistically significant warming (+2.5 K to +5 K) is evident throughout the troposphere at all sites, with seasonal changes in the +3 K to +9 K range near the surface at 1000 hPa. The recent (1994–2005) tropospheric warming has dominated the 1964–2005 lower troposphere temperature change, despite 1964–1982 upper-tropospheric cooling.” Box, J. E., and A. E. Cohen (2006), Geophys. Res. Lett., 33, L12706, doi:10.1029/2006GL025723. [Full text]

Extending Greenland temperature records into the late eighteenth century – Vinther et al. (2006) “At present, continuous instrumental temperature records for Greenland reach back to the late nineteenth century at a few sites. Combining early observational records from locations along the south and west coasts, it has been possible to extend the overall record back to the year 1784. The new extended Greenland temperature record is 9% incomplete. There are, however, sufficient new data (an additional 74 complete winters and 52 complete summers) to provide a valuable indication of late eighteenth century and nineteenth century seasonal trends. Comparison of the previously published records with additional observational series digitized from Danish Meteorological Institute Yearbooks has also revealed inhomogeneities in some of the existing twentieth century temperature records. These problems have been eliminated in the new extended Greenland temperature record. A long homogeneous west Greenland instrumental temperature record is of great value for the interpretation of the growing number of Greenland ice core records. A first comparison of the new record with highly resolved Greenland ice core data is presented. Correlations between west Greenland winter temperatures and the ice core winter season proxy are found to be r = 0.67 and r = 0.60 for the periods 1785–1872 and 1873–1970, respectively.” Vinther, B. M., K. K. Andersen, P. D. Jones, K. R. Briffa, and J. Cappelen (2006), J. Geophys. Res., 111, D11105, doi:10.1029/2005JD006810. [Full text]

Ratio of the Greenland to global temperature change: Comparison of observations and climate modeling results – Chylek & Lohmann (2005) “Temperature changes over Greenland are of special interest due to a possible melting of the Greenland Ice Sheet and resulting sea level rise. General Circulation Models (GCMs) predict that the temperature changes in Greenland should proceed at a faster rate than the global temperature change. Until now there has been no confirmation that Greenland’s long-term temperature changes are related to the global warming and that they proceed faster than the global temperature change. Using double correlations between the Greenland temperature records, North Atlantic Oscillation (NAO) index and global temperature change we find a region of Greenland that is not affected by the NAO. Using this region as an indicator of Greenland’s temperature change that is related to global warming, we find that the ratio of the Greenland to global temperature change due to global warming is 2.2 in broad agreement with GCM predictions.” Chylek, P., and U. Lohmann (2005), Geophys. Res. Lett., 32, L14705, doi:10.1029/2005GL023552.

Global Warming and the Greenland Ice Sheet – Chylek et al. (2004) “The Greenland coastal temperatures have followed the early 20th century global warming trend. Since 1940, however, the Greenland coastal stations data have undergone predominantly a cooling trend. At the summit of the Greenland ice sheet the summer average temperature has decreased at the rate of 2.2 °C per decade since the beginning of the measurements in 1987. This suggests that the Greenland ice sheet and coastal regions are not following the current global warming trend. A considerable and rapid warming over all of coastal Greenland occurred in the 1920s when the average annual surface air temperature rose between 2 and 4 °C in less than ten years (at some stations the increase in winter temperature was as high as 6 °C). This rapid warming, at a time when the change in anthropogenic production of greenhouse gases was well below the current level, suggests a high natural variability in the regional climate. High anticorrelations (r = –0.84 to–0.93) between the NAO (North Atlantic Oscillation) index and Greenland temperature time series suggest a physical connection between these processes. Therefore, the future changes in the NAO and Northern Annular Mode may be of critical consequence to the future temperature forcing of the Greenland ice sheet melt rates.” Petr Chylek, Jason E. Box and Glen Lesins, Climatic Change, Volume 63, Numbers 1-2, 201-221, DOI: 10.1023/B:CLIM.0000018509.74228.03. [Full text]

Recent cooling in coastal southern Greenland and relation with the North Atlantic Oscillation – Hanna & Cappelen (2003) “Analysis of new data for eight stations in coastal southern Greenland, 1958–2001, shows a significant cooling (trend-line change −1.29°C for the 44 years), as do sea-surface temperatures in the adjacent part of the Labrador Sea, in contrast to global warming (+0.53°C over the same period). The land and sea temperature series follow similar patterns and are strongly correlated but with no obvious lead/lag either way. This cooling is significantly inversely correlated with an increased phase of the North Atlantic Oscillation (NAO) over the past few decades (r = −0.76), and will probably have significantly affected the mass balance of the Greenland Ice Sheet.” Hanna, E., and J. Cappelen (2003), Geophys. Res. Lett., 30(3), 1132, doi:10.1029/2002GL015797. [Full text]

Survey of Greenland instrumental temperature records: 1873–2001 – Box (2002) “Temporal and spatial variability are analysed in Greenland instrumental temperature records from 24 coastal and three ice sheet locations. Trends over the longest period available, 1873–2001, at Ilulissat/Jakobshavn indicate statistically significant warming in all seasons: 5°C in winter. Trends over the 1901–2000 century in southern Greenland indicate statistically significant spring and summer cooling. General periods of warming occurred from 1885 to 1947 and 1984 to 2001, and cooling occurred from 1955 to 1984. The standard period 1961–90 was marked by 1–2°C statistically significant cooling. In contrast to Northern Hemisphere mean temperatures, the 1990s do not contain the warmest years on record in Greenland. The warmest years in Greenland were 1932, 1947, 1960, and 1941. The coldest years were 1918, 1984, 1993, and 1972, several of which coincide with major volcanic eruptions. Over 1991–2000, statistically significant 2–4°C warming was observed in western Greenland, 1.1°C warming at the ice sheet summit (3200 m), although this is statistically insignificant. Annual temperature trends are dominated by winter variability. Much of the observed variability is shown to be linked with the North Atlantic oscillation (NAO), sea ice extent, and volcanism. The correlation of coastal temperature anomalies with the NAO is statistically significant, in autumn and winter at western and southern sites. Warming from 1873 to 1930 and subsequent cooling persists after the removal of the NAO signal. Temperature trends are often opposite between west and east Greenland. This apparent teleconnection is spurious, however, given insignificant east–west correlation values. Frequency peaks correspond with periods of 3.7, 14.3, 9.1, 5.5–6.0, 11.1, and 7.1 years in both temperature and NAO.” Jason E. Box, International Journal of Climatology, Volume 22, Issue 15, pages 1829–1847, December 2002, DOI: 10.1002/joc.852. [Full text]

Past Temperatures Directly from the Greenland Ice Sheet – Dahl-Jensen et al. (1998) “A Monte Carlo inverse method has been used on the temperature profiles measured down through the Greenland Ice Core Project (GRIP) borehole, at the summit of the Greenland Ice Sheet, and the Dye 3 borehole 865 kilometers farther south. The result is a 50,000-year-long temperature history at GRIP and a 7000-year history at Dye 3. The Last Glacial Maximum, the Climatic Optimum, the Medieval Warmth, the Little Ice Age, and a warm period at 1930 A.D. are resolved from the GRIP reconstruction with the amplitudes -23 kelvin, +2.5 kelvin, +1 kelvin, -1 kelvin, and +0.5 kelvin, respectively. The Dye 3 temperature is similar to the GRIP history but has an amplitude 1.5 times larger, indicating higher climatic variability there. The calculated terrestrial heat flow density from the GRIP inversion is 51.3 milliwatts per square meter.” D. Dahl-Jensen, K. Mosegaard, N. Gundestrup, G. D. Clow, S. J. Johnsen, A. W. Hansen, N. Balling, Science 9 October 1998: Vol. 282. no. 5387, pp. 268 – 271, DOI: 10.1126/science.282.5387.268. [Full text]

Variability of AVHRR-Derived Clear-Sky Surface Temperature over the Greenland Ice Sheet – Stroeve & Steffen (1998) “The Advanced Very High Resolution Radiometer is used to derive surface temperatures for one satellite pass under clear skies over the Greenland ice sheet from 1989 through 1993. The results of these temperatures are presented as monthly means, and their spatial and temporal variability are discussed. Accuracy of the dry snow surface temperatures is estimated to be better than 1 K during summer. This error is expected to increase during polar night due to problems in cloud identification. Results indicate the surface temperature of the Greenland ice sheet is strongly dominated by topography, with minimum surface temperatures associated with the high elevation regions. In the summer, maximum surface temperatures occur during July along the western coast and southern tip of the ice sheet. Minimum temperatures are found at the summit during summer and move farther north during polar night. Large interannual variability in surface temperatures occurs during winter associated with katabatic storm events. Summer temperatures show little variation, although 1992 stands out as being colder than the other years. The reason for the lower temperatures during 1992 is believed to be a result of the 1991 eruption of Mount Pinatubo.” Stroeve, Julienne, Konrad Steffen, 1998, J. Appl. Meteor., 37, 23–31. doi: 10.1175/1520-0450(1998)0372.0.CO;2. [Full text]

Recent warming in central Greenland? – Alley & Koci (1990) “Recent warming has occurred in near-surface firn in central Greenland, as shown by analysis of a 217m temperature profile from the GISP2 site. However, this warming falls within the range of natural variability and provides no clear evidence of a greenhouse signal.”
Alley, Richard B.; Koci, Bruce R., Annals of Glaciology, vol.14, pp.6-8, 1990. [Full text]

The climate of Greenland – Putnins (1970) As described by Box (2002): “Temperatures around Greenland have been analysed between 1880 and 1955 by Putnins (1970)… Putnins (1970) identified five temperature trend periods: 1880–95, 1895–1909, 1909–29, 1929–43, and 1943–55. The most consistent period was 1909–29, when steady warming occurred. Significant cooling is said to have occurred at all stations during 1929–43. The 1943–55 period was characterized by warming, except at Upernavik.” Putnins P. 1970. In Climates of the Polar Regions, Orvig S (ed.). World Survey of Climatology, 14. Elsevier: 3–113.

Papers on pre-industrial anthropogenic climate forcing

This is a list of papers on the effect of pre-industrial mankind to the climate. The list is not complete, and will most likely be updated in the future in order to make it more thorough and more representative.

Contribution of anthropogenic land cover change emissions to preindustrial atmospheric CO₂ – Reick et al. (2010) “Based on a recent reconstruction of anthropogenic land cover change (ALCC) we derive the associated CO₂ emissions since 800 AD by two independent methods: a bookkeeping approach and a process model. The results are compared with the preindustrial development of atmospheric CO₂ known from antarctic ice cores. Our results show that preindustrial CO₂ emissions from ALCC have been relevant for the preindustrial carbon cycle, although before 1750 AD their trace in atmospheric CO₂ is obscured by other processes of similar magnitude. After 1750 AD the situation is different: the steep increase in atmospheric CO₂ until 1850 AD – this is before fossil-fuel emissions rose to significant values – is to a substantial part explained by growing emissions from ALCC.”

Biophysical feedbacks between the Pleistocene megafauna extinction and climate: The first human-induced global warming? – Doughty et al. (2010) “A large increase in Betula during a narrow 1000 year window, ∼13,800 years before present (YBP) in Alaska and Yukon corresponded in time with the extinction of mammoths and the arrival of humans. Pollen data indicate the increase in Betula during this time was widespread across Siberia and Beringia. We hypothesize that Betula increased due to a combination of a warming climate and reduced herbivory following the extinction of the Pleistocene mega herbivores. The rapid increase in Betula modified land surface albedo which climate-model simulations indicate would cause an average net warming of ∼0.021°C per percent increase in high latitude (53–73°N) Betula cover. We hypothesize that the extinction of mammoths increased Betula cover, which would have warmed Siberia and Beringia by on average 0.2°C, but regionally by up to 1°C. If humans were partially responsible for the extinction of the mammoths, then human influences on global climate predate the origin of agriculture.”

The prehistoric and preindustrial deforestation of Europe – Kaplan et al. (2009) “Humans have transformed Europe’s landscapes since the establishment of the first agricultural societies in the mid-Holocene. The most important anthropogenic alteration of the natural environment was the clearing of forests to establish cropland and pasture, and the exploitation of forests for fuel wood and construction materials. While the archaeological and paleoecological record documents the time history of anthropogenic deforestation at numerous individual sites, to study the effect that prehistoric and preindustrial deforestation had on continental-scale carbon and water cycles we require spatially explicit maps of changing forest cover through time. Previous attempts to map preindustrial anthropogenic land use and land cover change addressed only the recent past, or relied on simplistic extrapolations of present day land use patterns to past conditions. In this study we created a very high resolution, annually resolved time series of anthropogenic deforestation in Europe over the past three millennia by 1) digitizing and synthesizing a database of population history for Europe and surrounding areas, 2) developing a model to simulate anthropogenic deforestation based on population density that handles technological progress, and 3) applying the database and model to a gridded dataset of land suitability for agriculture and pasture to simulate spatial and temporal trends in anthropogenic deforestation. Our model results provide reasonable estimations of deforestation in Europe when compared to historical accounts. We simulate extensive European deforestation at 1000 BC, implying that past attempts to quantify anthropogenic perturbation of the Holocene carbon cycle may have greatly underestimated early human impact on the climate system.” Jed O. Kaplan, Kristen M. Krumhardt, and Niklaus Zimmermann, The prehistoric and preindustrial deforestation of Europe, Quaternary Science Reviews, Volume 28, Issues 27-28, December 2009, Pages 3016-3034, doi:10.1016/j.quascirev.2009.09.028. [Full text]

Effects of human land-use on the global carbon cycle during the last 6,000 years – Olofsson & Hickler (2008) “Humanity has become a major player within the Earth system, particularly by transforming large parts of the land surface and by altering the gaseous composition of the atmosphere. Deforestation for agricultural purposes started thousands of years ago and might have resulted in a detectable human influence on climate much earlier than the industrial revolution. This study presents a first attempt to estimate the impact of human land-use on the global carbon cycle over the last 6,000 years. A global gridded data set for the spread of permanent and non-permanent agriculture over this time period was developed and integrated within the Lund-Potsdam-Jena Dynamic Global Vegetation Model (LPJ-DGVM). The model was run with and without human land-use, and the difference in terrestrial carbon storage was calculated as an estimate of anthropogenic carbon release to the atmosphere. The modelled total carbon release during the industrial period (a.d. 1850–1990) was 148 gigatons of carbon (GtC), of which 33 GtC originated from non-permanent agriculture. For pre-industrial times (4000 b.c.–a.d. 1850), the net carbon release was 79 GtC from permanent agriculture with an additional 35 GtC from non-permanent agriculture. The modelled pre-industrial carbon release was considerably lower than would be required for a substantial influence on the climate system.” Jörgen Olofsson and Thomas Hickler, Vegetation History and Archaeobotany, Volume 17, Number 5, 605-615, DOI: 10.1007/s00334-007-0126-6. [Full text]

Using multiple archives to understand past and present climate–human–environment interactions: the lake Erhai catchment, Yunnan Province, China – Dearing et al. (2008) “A 6.48 m sediment core sequence from Erhai lake, Yunnan Province, provides a multi-proxy record of Holocene environmental evolution and human activity in southwest China. These sedimentary records provide proxy time series for catchment vegetation, flooding, soil erosion, sediment sources and metal workings. They are complemented by independent regional climate time-series from speleothems, archaeological records of human habitation, and a detailed documented environmental history. The article attempts to integrate these data sources to provide a Holocene scale record of environmental change and human–environment interactions. These interactions are analysed in order to identify the roles of climate and social drivers on environmental change, and the lessons that may be learned about the future sustainability of the landscape. The main conclusions are: lake sediment evidence for human impacts from at least 7,500 cal year BP is supported by a terrestrial record of cultural horizons that may extend back to ∼9,000 cal year BP. A major shift in the pollen assemblage, defined by detrended correspondence analysis, at ∼4,800 cal year BP marks the transition from a ‘nature-dominated’ to a ‘human-dominated’ landscape. From 4,300 cal year BP, a change in river discharge responses may signal the beginning of hydraulic modification through drainage and irrigation. Major increases in disturbed land taxa and loss of forest taxa from 2,200 cal year BP onward, also associated with the start of significant topsoil erosion, register the expansion of agriculture by Han peoples. It is also the start of silver smelting linked to trade along the SW Silk Road with Dali becoming a regional centre. Peak levels of disturbed land taxa, topsoil and gully erosion are associated with the rise and fall of the Nanzhao (CE 738–902) and Dali (CE 937–1253) Kingdoms, and the documented environmental crisis that occurred in the late Ming and Qing dynasties (CE 1644–1911). The crisis coincides with a stronger summer monsoon, but exploitation of marginal agricultural land is the main driver. These historical perspectives provide insight into the resilience and sustainability of the modern agricultural system. The largest threat comes from high magnitude-low frequency flooding of lower dry farmed terraces and irrigated valley plains. A sustainable future depends on reducing the use of high altitude and steep slopes for grazing and cultivation, maintaining engineered flood defences and terraces, and anticipating the behaviour of the summer monsoon.” J. A. Dearing, R. T. Jones, J. Shen, X. Yang, J. F. Boyle, G. C. Foster, D. S. Crook and M. J. D. Elvin, Using multiple archives to understand past and present climate–human–environment interactions: the lake Erhai catchment, Yunnan Province, China, 2008, Journal of Paleolimnology, Volume 40, Number 1, 3-31, DOI: 10.1007/s10933-007-9182-2.

Climate-human-environment interactions: resolving our past – Dearing (2006) “The paper reviews how we can learn from the past about climate-human-environment interactions at the present time, and in the future. It focuses on data sources for environmental change at local/regional and regional/global spatial scales, and shows the scope and limitations of each. It reviews alternative methods for learning from the past, including the increasing use of simulation models. The use of multiple records (observational, palaeoenvironmental, archaeological, documentary) in local case-studies is exemplified in a study from China, where independent records help unravel the complexity of interactions and provide a basis for assessing the resilience and sustainability of the landscape system. Holocene global records for Natural Forcings (e.g. climate and tectonics), Human Society and Ecosystems are reviewed, and the problems of reconstructing global records of processes that are only recorded at local scales examined. Existing regional/global records are used to speculate about the veracity of anthropogenic forcing of global climate, with specific consideration of the Ruddiman theory. The paper concludes that a full understanding of causes of earth system change through (at least) the Holocene can come only through the most rigorous reconstructions of climate, human activities and earth processes, and importantly their interactions, at all locations and at all scales. It follows that we need to promote inter-scale learning: regionalisation and generalisation of existing data would be useful first steps. There is now a need to develop long-term simulation models that can help anticipate complex ecosystem behaviour and environmental processes in the face of global environmental change – and resolving our past is an essential element in that endeavour.” Dearing, J. A.: Climate-human-environment interactions: resolving our past, Clim. Past, 2, 187-203, doi:10.5194/cp-2-187-2006, 2006. [Full text]

The Anthropogenic Greenhouse Era Began Thousands of Years Ago – Ruddiman (2003) “The anthropogenic era is generally thought to have begun 150 to 200 years ago, when the industrial revolution began producing CO₂ and CH₄ at rates sufficient to alter their compositions in the atmosphere. A different hypothesis is posed here: anthropogenic emissions of these gases first altered atmospheric concentrations thousands of years ago. This hypothesis is based on three arguments. (1) Cyclic variations in CO₂ and CH₄ driven by Earth-orbital changes during the last 350,000 years predict decreases throughout the Holocene, but the CO₂ trend began ananomalous increase 8000 years ago, and the CH₄ trend did so 5000 years ago.(2) Published explanations for these mid- to late-Holocene gas increases basedon natural forcing can be rejected based on paleoclimatic evidence. (3) A wide array of archeological, cultural, historical and geologic evidence points to viable explanations tied to anthropogenic changes resulting from early agriculture in Eurasia, including the start of forest clearance by 8000 years ago and of rice irrigation by 5000 years ago. In recent millennia, the estimated warming caused by these early gas emissions reached a global-mean value of 0.8 °C and roughly 2 °C at high latitudes, large enough to have stopped a glaciation of northeastern Canada predicted by two kinds of climatic models. CO₂ oscillations of 10 ppm in the last 1000 years are toolarge to be explained by external (solar-volcanic) forcing, but they can be explained by outbreaks of bubonic plague that caused historically documented farm abandonment in western Eurasia. Forest regrowth on abandoned farms sequestered enough carbon to account for the observed CO2decreases. Plague-driven CO₂ changes were also a significant causal factor in temperature changes during the Little Ice Age (1300–1900 AD).” William F. Ruddiman, Climatic Change, Volume 61, Number 3, 261-293, DOI: 10.1023/B:CLIM.0000004577.17928.fa. [Full text]

The case for human causes of increased atmospheric CH₄ over the last 5000 years – Ruddiman & Thomson (2001) “We propose that humans significantly altered atmospheric CH₄ levels after 5000 years BP and that anthropogenic inputs just prior to the industrial revolution accounted for up to 25% of the CH₄ level of 725 ppb (parts per billion). We base this hypothesis on three arguments: (1) the 100 ppb increase in atmospheric CH₄ that occurred after 5000 years BP follows a pattern unprecedented in any prior orbitally driven change in the ice-core record; (2) non-anthropogenic explanations for this increase (expansion of boreal peat lands or tropical wetlands) are inconsistent with existing evidence; and (3) inefficient early rice farming is a quantitatively plausible means of producing anomalously large CH₄ inputs to the atmosphere prior to the industrial revolution. If the areas flooded for farming harbored abundant CH₄-producing weeds, disproportionately large amounts of CH₄ would have been produced in feeding relatively small pre-industrial populations.” [Full text]

On the origin and magnitude of pre-industrial anthropogenic CO₂ and CH₄ emissions – Kammen & Marino (1993) “The potential impact of human activity on the climate system, particularly as related to fossil fuel combustion, is widely acknowledged. However, little is known of the origin and magnitude of anthropogenic non-fossil emissions, although this activity currently contributes up to 40% of the global CO₂ emissions. Here we provide estimates of CO₂ and CH₄ emissions resulting from pre-industrial societies by combining historical demographic and archaeological data. Combustion of non-fossil carbon for domestic needs, small-scale industrial/craft activities and resulting from agricultural land management was significant, reaching about 1 Gt of carbon (GtC) as CO₂yr⁻¹ and 10 Tg of of carbon CH₄yr⁻¹ by 1800 A.D. This data implies a significant anthropogenic source of pre-industrial atmospheric greenhouse gases; consistent with estimates derived from carbon cycle models. We illustrate the contribution of archaeological data with two case studies: (i) estimates of CH₄ emissions from agricultural activity from the Maya Lowlands; and (ii) evidence of correlations between climatic and socio-economic conditions in North Atlantic Norse settlements. This work provides an improved baseline for studies of historic climate change, such as the Little Ice Age, as well as for evaluating strategies for mitigating current greenhouse gas emissions.”

New research from last week 42/2010

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as I write them. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news.

Very old news:

Before looking at the latest news, I want to point out an old study I came across. Here’s some very old news:

Next time when someone goes on and on about how carbon dioxide is meaningless because convection transmits heat to upper atmosphere, and how modern science has practically ignored the convection, show them Cunnington & Mitchell (1989) who already in 1980’s were studying how exactly convection affects climate sensitivity.

Published last week:

Ocean transporting heat to Arctic leads to more warming

A new study has looked at Arctic warming and sea ice. The study concentrated on the ocean heat transport. The results: “Those models which transport more energy to the Arctic show a stronger future warming, in the Arctic as well as globally. Larger heat transport to the Arctic, in particular in the Barents Sea, reduces the sea ice cover in this area. More radiation is then absorbed during summer months and is radiated back to the atmosphere in winter months. This process leads to an increase in the surface temperature and therefore to a stronger polar amplification. The models which show a larger global warming agree better with the observed sea ice extent in the Arctic. In general, these models also have a higher spatial resolution.” And conclusion: “These results suggest that higher resolution and greater complexity are beneficial in simulating the processes relevant in the Arctic, and that future warming in the high northern latitudes is likely to be near the upper range of model projections, consistant with recent evidence that many climate models underestimate Arctic sea ice decline.”

Citation: Irina Mahlstein and Reto Knutti, Ocean heat transport as a cause for model uncertainty in projected Arctic warming, Journal of Climate 2010, doi: 10.1175/2010JCLI3713.1. [abstract]

Positive low-cloud feedback from CERES and ECMWF data

Eitzen and others have studied how low-altitude cloud amount changes with sea surface temperature. Their data doesn’t cover very long period, only 5 years of data from CERES and from ECMWF reanalysis. The results: “First, the low cloud amount … and the logarithm of low cloud optical depth … tend to decrease while the net cloud radiative effect … becomes less negative as SST anomalies increase.” And: “The residual positive change in net cloud radiative effect … and small changes in low cloud amount … and decrease in the logarithm of optical depth … with SST are interpreted as a positive cloud feedback, with cloud optical depth feedback being the dominant contributor.” There are some differences regionally in the feedback amount: “with the largest positive feedbacks (~4 W m⁻² K⁻¹) in the southeast and northeast Atlantic regions and a slightly negative feedback (−0.2 W m⁻² K⁻¹) in the south-central Pacific region.”

Citation: Zachary A. Eitzen, Kuan-Man Xu, and Takmeng Wong, An Estimate of Low Cloud Feedbacks from Variations of Cloud Radiative and Physical Properties with Sea Surface Temperature on Interannual Time Scales, Journal of Climate 2010, doi: 10.1175/2010JCLI3670.1. [abstract]

Whales measuring ocean temperature

This article reports narwhals measuring ocean temperature: “Fourteen narwhals were instrumented with satellite-linked time-depth-temperature recorders between 2005 and 2007.” The whales took dives and temperatures were recorded. Results: “Whale data correlated well with climatological temperature maxima; however, they were on average 0.9°C warmer ±0.6°C (P < 0.001). Furthermore, climatology data overestimated the winter surface isothermal layer thickness by 50–80 m. Our results suggest the previously documented warming in Baffin Bay has continued through 2007 and is associated with a warmer West Greenland Current in both of its constituent water masses." But really the point of this article is: “This research demonstrates the feasibility of using narwhals as ocean observation platforms in inaccessible Arctic areas where dense sea ice prevents regular oceanographic measurements and where innate site fidelity, affinity for winter pack ice, and multiple daily dives to >1700 m offer a useful opportunity to sample the area.”

Citation: Laidre, K. L., M. P. Heide-Jørgensen, W. Ermold, and M. Steele (2010), Narwhals document continued warming of southern Baffin Bay, J. Geophys. Res., 115, C10049, doi:10.1029/2009JC005820. [abstract]

Sea level spectrum shows global sea level rising

A new study has taken the spectrum of sea level variations. In addition to that: “We present a method of plotting spectral information as color, focusing on periods between 2 and 24 weeks, which shows that significant spatial variations in the spectral shape exist and contain useful dynamical information.” With this method: “For global mean sea level, the statistical error reduces to 0.1 mm/yr over 12 years, with only 2 years needed to detect a 1 mm/yr trend. We find significant regional differences in trend from the global mean. The patterns of these regional differences are indicative of a sea level trend dominated by dynamical ocean processes over this period.”

Citation: Hughes, C. W., and S. D. P. Williams (2010), The color of sea level: Importance of spatial variations in spectral shape for assessing the significance of trends, J. Geophys. Res., 115, C10048, doi:10.1029/2010JC006102. [abstract]

Cryo-hydrologic warming making it easier for Greenland to melt

Cryo-hydrologic (CH) warming means that the melt-water in the surface of the ice-sheet warms the ice which then of course melts some more. A new study has used a thermal model of ice sheets including the CH-warming to research the situation. The CH-warming does wonders to the timescales of the ice-sheet melt: “The corresponding time-scale of thermal response is of the order of years-decades, in contrast to conventional estimates of thermal response time-scales based on vertical conduction through ice (∼10^2–3 m thick), which are of the order of centuries to millennia.” That doesn’t sound very promising. Is it occurring yet? Yep: “We show that CH warming is already occurring along the west coast of Greenland. Increased temperatures resulting from CH warming will reduce ice viscosity and thus contribute to faster ice flow.”

Citation: Phillips, T., H. Rajaram, and K. Steffen (2010), Cryo-hydrologic warming: A potential mechanism for rapid thermal response of ice sheets, Geophys. Res. Lett., 37, L20503, doi:10.1029/2010GL044397. [abstract]

Rapid climate change lessons from the past

Rapid climate changes have occurred in the past, as can be seen in the geological record. The journal Global and Planetary Change is publishing a special issue on the rapid climate changes. The introduction paper has now been published and the abstract says: “Rapid climate changes are known to have occurred over time periods equal to or even less than a human lifespan: moreover, their impacts on the global system are sufficiently large to have had significant societal impacts.” We currently seem to be facing a rapid climate change, so the knowledge of rapid climate changes in the past is important. The introductory paper gives an overview of the papers in the special issue. The overall conclusion is: “The results confirm the importance of freshwater forcing in triggering changes in Atlantic Meridional Overturning Circulation (MOC) and the close links between MOC and rapid climate change.”

Citation: Jonathan Holmes, John Lowe, Eric Wolff, and Meric Srokosz, Rapid climate change: Lessons from the recent geological past, Global and Planetary Change, doi:10.1016/j.gloplacha.2010.10.005. [abstract]

Northern Annular Mode causes uncertainties to future northern climate

The Northern Annular Mode (NAM) is a variability in the atmosphere that has an effect to climate in Northern Hemisphere. NAM is expected to change with increasing greenhouse effect. The changes in NAM are not known very well, the climate models give different kinds of responses to greenhouse forcing. A new study has looked how much uncertainty NAM introduces to northern regional climate. That was estimated from the spread of different model results. The result: “We show that the intermodel spread of the future NAM projections account for up to 40% of the variance of the surface temperature and precipitation projections over some regions in Eurasia and North America across the simulations. This result implies that the uncertainty in the future NAM makes a considerable contribution into the overall uncertainty in regional climate predictions.”

Citation: Karpechko, A. Yu. (2010), Uncertainties in future climate attributable to uncertainties in future Northern Annular Mode trend, Geophys. Res. Lett., 37, L20702, doi:10.1029/2010GL044717. [abstract]

Pine Island Glacier contribution to sea level less than 3 cm

Pine Island Glacier (PIG) in Antarctica might contribute considerably to the global sea level rise as PIG is losing mass rapidly. A new study has created a model for studying that contribution. The reasons for mass loss are discussed: “While oceanic melt likely played the leading role in recent thinning and retreat, we find that the particular grounding-line geometry with an extended ice plain in the 1990s made it susceptible to such forcing. Our model further indicates that while the rate of grounding-line retreat should diminish soon, the glacier’s mass loss may continue at rates similar to, or moderately elevated from, the present.” Then on the rate of mass loss: “While substantial, our model-derived maximum rate of 2.7 cm/century is considerably smaller than previous heuristically-derived bounds on the sea-level contribution.”

Citation: Joughin, I., B. E. Smith, and D. M. Holland (2010), Sensitivity of 21st century sea level to ocean-induced thinning of Pine Island Glacier, Antarctica, Geophys. Res. Lett., 37, L20502, doi:10.1029/2010GL044819. [abstract]

Measuring the heat flux to the oceans

The net air–sea surface heat flux has been measured in North Pacific and North Atlantic between 1984 and 2004. It turns out that the net heat flux is going into the oceans in most of the measured areas. Both in the areas of heat flux going into the oceans and in the areas of heat flux going into the atmosphere the underlying causes can be traced to the global warming.

Citation: Gen Li, Baohua Ren, Jianqiu Zheng and Chengyun Yang, Net air–sea surface heat flux during 1984–2004 over the North Pacific and North Atlantic oceans (10°N–50°N): annual mean climatology and trend, 2010, Theoretical and Applied Climatology, DOI: 10.1007/s00704-010-0351-2. [abstract]

Biodiversity suffers in Europe with climate change

A new study has used environmental and climate models to estimate stable area of species and species turnover. Climate change will have remarkable effects: “We show that if global temperature increases, then both species turnover will increase, and mean stable area of species will decrease in all biomes. The most dramatic changes will occur in Northern Europe, where more than 35% of the species composition in 2100 will be new for that region, and in Southern Europe, where up to 25% of the species now present will have disappeared under the climatic circumstances forecasted for 2100.”

Citation: Rob Alkemade, Michel Bakkenes and Bas Eickhout, Towards a general relationship between climate change and biodiversity: an example for plant species in Europe, Regional Environmental Change, DOI: 10.1007/s10113-010-0161-1. [abstract]

Review article on global drought situation

Apparently there are some original research in this work as well. I don’t need to say much about this as there is a press release on this from UCAR.

Citation: Aiguo Dai, Drought under global warming: a review, Wiley Interdisciplinary Reviews: Climate Change, 2010, DOI: 10.1002/wcc.81. [abstract, full text]

Multiyear ice melting rapidly in the Beaufort Sea

New study by Kwok & Cunningham has made estimates on the multiyear ice trends in Beaufort Sea: “For the summers of 1993 through 2009, we estimate the loss of multiyear sea ice (MYI) area in the Beaufort Sea due to melt.” The loss of area was: “Net loss of area (with fractional MYI coverage >50%) over the 17-year period is ∼900 × 10³ km². Three-quarters of that area, ∼10% of the area of the Arctic Ocean, was lost after 2000.” (The “∼” is most likely a “~”.) Rest of the abstract is worth quoting as well: “There is a clear positive trend in the record, with a distinct peak of 213 × 10³ km² in 2008; this is twice the summer outflow at the Fram Strait that year. The net melt area of 490 × 10³ km² between 2005 and 2008 accounts for nearly 32% of the net loss of 1.54 × 10⁶ km² of Arctic Ocean MYI coverage over the same period. Volume loss, for the years with ICESat thickness (2004–2009), is highest at 473 km³ in 2008 followed by 320 km³ in 2007. Net loss in MYI volume for the six summers is ∼1400 km³. This is ∼20% of the loss in MYI volume of 6300 km³ during 2004–2008. This adds to the freshwater content of the Arctic Ocean and locally to the freshening of the Beaufort Gyre.”

Citation: Kwok, R., and G. F. Cunningham (2010), Contribution of melt in the Beaufort Sea to the decline in Arctic multiyear sea ice coverage: 1993–2009, Geophys. Res. Lett., 37, L20501, doi:10.1029/2010GL044678. [abstract]

Back in 1991: “Response to Skeptics of Global Warming”

About 20 years ago, William Kellogg wrote an article called “Response to Skeptics of Global Warming” which was published in Bulletin of the American Meteorological Society in April, 1991 (full text here). Let us see what were the issues then and what was Kellogg’s response.

Introduction

By 1991, the attention towards the anthropogenic global warming had increased considerably. Kellogg descibes how the greenhouse theory had been well accepted long time ago. The theory also had been tested by observations and observations also showed that the concentration of greenhouse gases were increasing in the atmosphere.

First controversial topic Kellogg mentions is this:

First, there is good justification for the view that there are just too many interacting factors involved in the extraordinarily complex system that determines our climate, and that we can never hope to understand all those interactions.

This is the familiar issue about the climate sensitivity and its uncertainties. The skeptic view that arises from this, as Kellogg describes it, is that no action should be made before the uncertainties about climate sensitivity have been reduced.

Second controversy:

A second motivation for resisting the temptation to take such action is the notion, being advanced in some quarters with considerable vehemence, that a global warming will be beneficial to the world as a whole, and we should do nothing to slow it down.

I quite like the phrase ‘resisting the temptation to take action’. 🙂 Kellogg also notes the role of the media:

In the past year or two the media have reported the statements of a small cadre of scientists who disagree with the conclusions of the majority of those who are doing research on the climate system.

I’m resisting the temptation to ask after each quote here if they sound familiar. With these introductory themes Kellogg starts to address the skeptic arguments:

Let us take a critical look at what the skeptics, or “environmental naysayers”, are saying. We will not try to deal with every one of the points raised by them, but the following will discuss the more interesting and widely quoted ones.

So it seems that Kellogg pioneered the field John Cook is now mastering. The part about the “naysayers” has to do with Kellogg having just quoted a comment by Senator Tim Wirth.

The arguments and the response

Kellogg first addresses the argument about the uncertainty in climate sensitivity:

Yet the five or so most advanced climate models, developed over a period of many years by top notch teams, have all come to essentially the same conclusion: The global average surface temperature would probably rise by about 2 to 5 K if the greenhouse gas concentration were maintained at double the pre-Industrial Revolution level, which for carbon dioxide was 270 to 280 parts per million (ppmv).

However, Kellogg also points out that the models have problems in their resolution and other problems, but also that modelers recognize those issues.

The question of the recent surface temperatures in 1991 was stated as: “Why have we not already seen the greenhouse warming”? Kellogg says that the answer to the question is not clear but that there has been a warming trend in the past 100 years but that there are natural variability and other factors that can contribute to the warming. Kellogg then points out that the warming from greenhouse gases is a global phenomenon and should therefore show up in global temperature – and it does (and did in 1991). By that time, the global temperature record had just been complemented with sea surface temperatures, so there were newly acquired confidence to the record. Let us take another “sound familiar?” quote:

[Global average temperature] rose quite fast from 1900 to 1940, then more or less leveled off until 1970, and since then the decade of the 1980s has witnessed five record breaking years…

Then about the skeptic view:

…some still express doubts that there has already been a long-term warming due to the greenhouse effect (Barnett and Schlesinger 1987; Seitz et al. 1990; Lindzen 1990; Ellsaesser 1990; Reifsnyder 1989). It is not significant, they sometimes say.

Kellogg then performs a statistical test on the global average temperature during the 20th century and concludes that the signal has a over 98 % probability to be real. But he also points out that due to natural variability and other factors the attribution of the warming to the greenhouse effect is problematic. He concludes on this issue:

So some of the more cautious policy makers who are listening to our debate can, at least for the time being, cite the IPCC report and argue that they have another ten years or so to wait before remedial action will be justified by “unequivocal” evidence.

The next issue is the United States temperature record. In 1991, the situation was that there were some papers showing that lower 48 states of United States had not warmed in last hundred years. Kellogg describes the media take on the issue:

The press has published this finding as evidence against the conclusion that the world had become warmer. What they often fail to add was that the U.S. (lower 48) occupies less than 5% of the area of the globe, so what happens in the U.S. can hardly be considered to apply to the world as a whole.

Kellogg the points out that it is actually only the eastern part of the United States that had experienced cooling. He also adds that the effect of urban heat island complicates things further so that there actually should be even more cooling showing in the United States temperature record. To this he says:

However, even if this bias exists at urban climate observing stations on land in other parts of the world, it can hardly have an influence on the COADS marine temperature record. Thus, the combined global surface temperature record, shown in Fig. 1, must be accurate enough to demonstrate a real warming trend, and the urban heat island effect on the land stations is considered to have less than a 0.05 K effect on the average (Folland et al. 1990).

Kellogg then addresses a claim by Lindzen that global warming has not begun because North Atlantic has been cooling slightly during about 50 years before 1991. Kellogg says this is just another regional result and that land areas have warmed faster which is no surprise because in ocean temperature there are other factors than radiation balance slowing the ocean warming. Kellogg the explains some model results relevant to the explanation of this ocean cooling.

Next claim to be addressed is the claim that satellite records show that there’s no warming. There had been a NASA report describing 10 years of satellite data which showed no clear trends. There had been some claims that this means there’s no global warming. Kellogg explains why this is not so:

The point is simply that one cannot demonstrate a 100-year trend by looking at a 10-year segment of the record, particularly when there is so much natural fluctuation in the record.

That is not all, there’s another problem with satellite records:

The oxygen emission measured by the satellite instrument actually comes from a region of the atmosphere extending from near the ground up to the tropopause, and it may sometimes include part of the lower stratosphere. … Thus, the temperature of a very deep portion of the atmosphere is being sampled, and the upper part of this layer is expected theoretically to show a cooling trend rather than warming. This fact suggests that such microwave observations may not be suitable for monitoring the year-to-year progression of the greenhouse effect, during which the warming should occur mainly in the lower part of the troposphere.

To the claim that the observed warming trend is due to sun, Kellogg says that while you can explain some of the fluctuations in climate records by solar and volcanic activity the explanation of longer term trends with them is problematic:

However, no long-term trend is evidenced unless the progressively important greenhouse effect is also introduced as a third-forcing function (Hansen et al. 1981; Gilliland 1982).

Kellogg then discusses some detailed issues regarding the solar forcing.

Next issue is the negative feedbacks in the climate system. Apparently, there had been some claims that there might be some strong negative feedbacks which are not included in the climate models. That would then lower the climate sensitivity. Lindzen’s iris hypothesis is mentioned specifically. Kellogg makes some objections to the hypothesis including some observations showing that water vapor in the troposphere has increased which is against Lindzen’s hypothesis. Kellogg concludes:

It thus appears that the critics of currently accepted assessments of climate change are going to have to continue their search for some powerful and credible (but hitherto overlooked) negative feedback mechanism that will greatly reduce the apparent sensitivity of the earth’s climate system to an increase of the greenhouse gases.

The cloudiness problem is discussed next. The clouds are a strong factor in climate and their modelling is difficult because of several factors including the coarse resolution of the models. Kellogg points out some observations:

Over the past 30 years the tropics have gotten warmer, especially over the oceans (Flohn and Kapala 1989), and in this period high clouds in the tropics (Ci and Cb) have increased, while lower and middle clouds (Cu and St) have decreased (London et al. 1991). Both of these trends in cloudiness contribute to a positive feedback, or warming.

Kellogg then describes some model results on cloudiness. There is a big spread in their results, so it seems that models need to be improved relating to the clouds, but observational evidence seems to be pointing to positive rather than negative feedback.

Then Kellogg moves on to the claim that climate change will be beneficial. This was of course rather controversial subject back then (and still is to some extent) so Kellogg points out that the majority of climate scientists see the climate change effects to be non-beneficial on the whole.

Looking back on Kellogg’s article now makes me think that it could very well have been written this year on some of its parts. Science has moved ahead on many issues discussed. Many of them were non-issues already in 1991, as Kellogg shows. Yet you see all of the claims discussed here presented even today, unchanged.

References

Kellogg, William W., 1991: Response to Skeptics of Global Warming. Bull. Amer. Meteor. Soc., 72, 499–511. [abstract, full text]

New research from last week 41/2010

Here is the new research published last week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as I write them. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news.

Published last week:

– An effort to homogenize the radiosonde humidity records has been made in a new study using new approach. They describe the resulting tropospheric humidity data set: “The adjusted daily DPD has much smaller and spatially more coherent trends during 1973–2008 than the raw data. It implies only small changes in relative humidity in the lower and middle troposphere.” Also noteworthy is: “The DPD adjustment yields a different pattern of change in humidity parameters compared to the apparent trends from the raw data. The adjusted estimates show an increase in tropospheric water vapor globally”
Citation: Aiguo Dai and Junhong Wang, Peter W. Thorne, David E. Parker, Leopold Haimberger, Xiaolan L. Wang, Journal of Climate 2010, doi: 10.1175/2010JCLI3816.1. [abstract]

– A new study looks at temperature proxies based on pollen and tree-rings. Pollen data is commonly thought to be a long term proxy and not so good short term proxy while tree-rings are thought to capture short term variations better than long term variations. The new study uses proxies from high-latitude Europe (probably some from my home country Finland!). The pollen and tree-ring data are compared and it turns out they compare well in long term variability. They show similar variability on centennial and longer scales. The resulting reconstruction is described: “Over longer intervals, our new proxy-fusions cover the climatic reversals of the Medieval Climate Anomaly (during the 10th to 13th centuries), Little Ice Age (during the 14th to 19th centuries), and 20th century warming. The warmest spells occurred in association with the Medieval Climate Anomaly and during the 20th century. The coolest intervals occurred in relation to Little Ice Age conditions. The new reconstructions show that decadal temperature amplitude has been approximately 2.5 °C in the past and thus considerably larger than inferred from spatially large-scale estimates of temperature anomalies.”
Citation: Samuli Helama, Heikki Seppä, H. John B. Birks, and Anne E. Bjune, Reconciling pollen-stratigraphical and tree-ring evidence for high- and low-frequency temperature variability in the past millennium, Quaternary Science Reviews, 2010, doi:10.1016/j.quascirev.2010.09.012. [abstract]

– New research article says that the existing explanation for the extinction of Neanderthals are not satisfactory: “The two main factors currently proposed are the arrival of a modern human competitor and/or the aptitude of the Neanderthals to survive rapidly changing climatic conditions. None of these hypotheses is fully satisfactory because the Neanderthals experienced other large climatic changes and the duration of overlap of the two populations remains largely unknown and even uncertain.” The article points out that two geomagnetic events are synchronous with the Neandertal extinction; the Laschamp event and the Mono Lake event. These were the most dramatic events in the history of Neanderthals. The article explains why the events would have been important in the extinction: “During this period the geomagnetic field strength was considerably reduced and the shielding efficiency of the magnetosphere lowered, leaving energetic particles reach latitudes as low as 30°. The enhanced flux of high-energy protons (linked to solar activity) into the atmosphere yielded significant ozone depletion down to latitudes of 40–45°. A direct consequence was an increase of the UV-B radiations at the surface which might have reached at least 15–20% in Europe with significant impacts on health of human populations. We suggest that these conditions, added to some other factors, contributed to the demise of Neanderthal population.”
Citation: Jean-Pierre Valet and Hélène Valladas, The Laschamp-Mono lake geomagnetic events and the extinction of Neanderthal: A causal link or a coincidence?, Quaternary Science Reviews, 2010, doi:10.1016/j.quascirev.2010.09.010. [abstract]

– New study has made an effort to constrain climate sensitivity. They point out that current range of 2 – 4.5 K has lot of uncertainty. They describe their methods: “Simple indices of spatial radiation patterns are used here to establish a relationship between an observable radiative quantity and the equilibrium climate sensitivity. The indices are computed for the CMIP3 multi-model data set and offer a possibility to constrain climate sensitivity by considering radiation patterns in the climate system.” They find high correlations between the indices and climate sensitivity in certain cases. Resulting climate sensitivities between different data sets are: CERES – 2.7 to 4 K, ERBE (the dataset Lindzen & Choi used to claim negative feedback) – 1.7 to 3.8 K, ISCCP – 2.9 to 3.7 K, MERRA – 2.8 to 4.1 K, JRA25 – 3 to 4.2 K, ERA-Interim – 2.7 to 3.9 K, ERA-40 – 3 to 4 K, NCEP – 3.1 to 4.7 K. Conclusion: “For the aggregation of the reference datasets, the climate sensitivity is unlikely to be below 2.9 K within the framework of our study, whereas values exceeding 4.5 K cannot be excluded from our analysis.”
Citation: Markus Huber, Irina Mahlstein and Martin Wild, John Fasullo, Reto Knutti, Constraints on climate sensitivity from radiation patterns in climate models, Journal of Climate 2010, doi: 10.1175/2010JCLI3403.1. [abstract]

– This one was mentioned in the paper that was just published by the Science (the one about “climate control knob”). Here they determine the relative contributions of greenhouse gases and the result is 50 % from water vapor, 25 % from clouds, 20 % from CO₂, and the contribution from other GHGs is small. The abstract mentions in the end: “All other absorbers play only minor roles. In a doubled CO2 scenario, this allocation is essentially unchanged, even though the magnitude of the total greenhouse effect is significantly larger than the initial radiative forcing, underscoring the importance of feedbacks from water vapor and clouds to climate sensitivity.”
Citation: Schmidt, G. A., R. A. Ruedy, R. L. Miller, and A. A. Lacis (2010), Attribution of the present-day total greenhouse effect, J. Geophys. Res., 115, D20106, doi:10.1029/2010JD014287. [abstract, full text, GISS page with research brief and news release]

– Dessler & Davis have studied the situation with tropospheric humidity. There is a situation that while generally a positive water vapor feedback is observed, the NCEP/NCAR reanalysis shows long term water vapor feedback to be negative especially in tropics. In this new study, five different reanalyses are being studied together. It is found that all five reanalyses: “…unanimously agree that specific humidity generally increases in response to short-term climate variations (e.g., El Niño).” However, in long term analysis, NCEP/NCAR reanalysis shows decreasing tropical mid and upper tropospheric specific humidity in response to decadal warming, but all other four reanalyses show increasing tropical mid and upper tropospheric specific humidity in response to decadal warming. Conclusion: “We conclude from this that it is doubtful that these negative long-term specific humidity trends in the NCEP/NCAR reanalysis are realistic for several reasons.” First reason is that newer reanalyses have improved features specifically for making the long term performance more accurate, so older reanalyses, like NCEP/NCAR are likely to be more inaccurate in long term trends. Second reason is that NCEP/NCAR is the only reanalysis that doesn’t use satellite measurements in addition to radiosonde measurements. And final two points: “Third, the NCEP/NCAR reanalysis exhibits a large bias in tropical upper tropospheric specific humidity. And finally, we point out that there exists no theoretical support for having a positive short-term water vapor feedback and a negative long-term one.”
Citation: Dessler, A. E., and S. M. Davis (2010), Trends in tropospheric humidity from reanalysis systems, J. Geophys. Res., 115, D19127, doi:10.1029/2010JD014192. [abstract]

– “Boreal lakes are known to be supersaturated with CO₂ and to be significant sources of CO₂ to the atmosphere”, the abstract of a new research article starts. Small boreal streams have been studied and they apparently are even moire supersaturated with carbon dioxide, so the small boreal streams are also a carbon dioxide emission source. The emissions from them are surprisingly large: “Small boreal streams account for an annual (ice-free seasons) average of 8.0% and a seasonal high of 34.4% of the total CO₂ evaded from streams and lakes.” Emissions are greatest in summer from the streams.
Citation: Koprivnjak, J.-F., P. J. Dillon, and L. A. Molot (2010), Importance of CO2 evasion from small boreal streams, Global Biogeochem. Cycles, 24, GB4003, doi:10.1029/2009GB003723. [abstract]

– New research article reports an analysis of the timing when ocean acidification causes corrosive conditions to aragonite using species. Earlier this condition has been expected to begin in 2015. By using both observations and models, researchers found that sea ice cover and deep-water entrainment during winter causes the ocean to take in less carbon dioxide than expected. Their conclusion: “This means that instead of corrosive ‘acidified’ waters beginning as early as the winter of 2015, anthropogenic CO₂ disequilibrium delays its onset by up to 30 years, giving this Antarctic marine ecosystem a several decade reprieve to corrosive conditions.”
Citation: McNeil, B. I., A. Tagliabue, and C. Sweeney (2010), A multi-decadal delay in the onset of corrosive ‘acidified’ waters in the Ross Sea of Antarctica due to strong air-sea CO₂ disequilibrium, Geophys. Res. Lett., 37, L19607, doi:10.1029/2010GL044597. [abstract]

– New study has compared model simulated extreme temperatures to observed extreme temperatures both regionally and globally. Extreme temperatures here mean annual minimums and maximums of daily minimum and maximum temperatures. The results suggest that the anthropogenic forcing can be seen in the extreme temperatures globally and regionally in many places over land areas. Detection of anthropogenic forcing seems to be strongest in annual maximum of daily minimum temperatures. Minimum extremes have changed from events that happened once every 20 years in 1960’s to similar events happening now once in over 30 years. Maximum extremes show rather different change though: “In contrast, waiting times for circa 1960s 20-year extremes of annual maximum daily minimum and daily maximum temperatures are estimated to have decreased to less than 10 and 15 years respectively.”
Citation: Francis W. Zwiers, Xuebin Zhang, Yang Feng, Anthropogenic Influence on Long Return Period Daily Temperature Extremes at Regional Scales, Journal of Climate, 2010, doi: 10.1175/2010JCLI3908.1. [abstract]

– The urban heat island effect and global warming have warmed up the groundwater below the cities. A new study looks how much heat there actually is: “Detailed groundwater temperature measurements in Cologne (Germany) and Winnipeg (Canada) reveal high subsurface temperature distributions in the centers of both cities and indicate a warming trend of up to 5 °C.” This might have interesting propects: “The results show, for example, that, by decreasing the 20 m thick urban aquifer’s temperature by 2 °C, the amount of extractable geothermal energy beneath Cologne is 2.5 times the residential heating demand of the whole city. The geothermal potential in other cities such as Shanghai and Tokyo is shown to supply heating demand even for decades.”
Citation: Ke Zhu, Philipp Blum, Grant Ferguson, Klaus-Dieter Balke and Peter Bayer, The geothermal potential of urban heat islands, Environmental Research Letters, 2010, Volume 5, Number 4, doi: 10.1088/1748-9326/5/4/044002. [abstract]

– New study reports direct measurements of the contribution of continental ice and water to the global sea level. GRACE satellite data was used to measure mass exchange between land and ocean. Conclusion: “We estimate that the total ice and water mass loss from the continents is causing global mean sea-level to rise by 1.0 ± 0.4 mm/yr. Isolating the ice and hydrological signals, we find that the former is the sole net contributor to the global mean, while the latter dominates regional RSL changes in many coastal areas.”
Citation: Riva, R. E. M., J. L. Bamber, D. A. Lavallée, and B. Wouters (2010), Sea-level fingerprint of continental water and ice mass change from GRACE, Geophys. Res. Lett., 37, L19605, doi:10.1029/2010GL044770. [abstract]

– Using hydrodynamic and carbon model, a new study has investigated the influence of hurrican passage to air sea carbon dioxide exchange: “The results showed that the sea surface temperature cooling was the dominant cause of the decrease of surface pCO₂, while the entrainment of water with higher CO₂ levels partially offset the cooling-induced decrease.” Hurricane effect was rather wide: “The impact of the hurricane on the local air-sea CO₂ exchange extended to about 100 km on both sides of the hurricane track.” On the amount of carbon dioxide: “The whole passage of Hurricane Frances was estimated to have caused a CO2 efflux of about 3.504–10.363 Tg (1 Tg = 10¹² g) C from ocean to the atmosphere. Globally, hurricanes in 2004 were estimated to have released a CO₂ efflux of 0.047–0.141 Pg (1 Pg = 10¹⁵ g) C in total when extrapolating from Hurricane Frances. Under our assumptions, the CO₂ efflux caused by the passages of global hurricanes should have increased by about 71.2%–75.0% in past decades.”
Citation: Huang, P., and J. Imberger (2010), Variation of pCO₂ in ocean surface water in response to the passage of a hurricane, J. Geophys. Res., 115, C10024, doi:10.1029/2010JC006185. [abstract]

– A PNAS article to be published next week says that a slow-down of population growth could decrease carbon dioxide emissions: “The study showed that a slowing of population growth, following one of the slower growth paths considered plausible by demographers at the United Nations, could contribute to significantly reducing greenhouse gas emissions. The researchers found that such slow growth paths by 2050 could account for 16 to 29 percent of the emissions reductions thought necessary to keep global temperatures from causing serious impacts.” Another factor is increasing urbanization which according to this study increases emissions because urban citizens tend to produce and consume more. Population aging is a factor that decreases emissions because older people are less productive due to low percentage of them participating in labor force.
Source: Population trends: Another influence on climate change – UCAR news

– A study using chemistry climate model looked if climate change will increase the ozone depletion. They find some increase in certain years but in other years there are compensating effects. Overall climate change doesn’t seem to have much effect to ozone depletion. “In years of strong geomagnetic activity, similar to that observed in 2003, an additional polar ozone loss of up to 0.4 μmol/mol at 5 hPa is found in the Southern Hemisphere. However, this would be approximately compensated by an ozone enhancement originating from a stronger poleward transport of ozone from lower latitudes caused by a strengthened Brewer-Dobson circulation, as well as by slower photochemical ozone loss reactions in a stratosphere cooled by risen greenhouse gas concentrations. In the Northern Hemisphere the EEP NO_x effect appears to lose importance due to the different nature of the climate-change induced circulation changes.”
Citation: Baumgaertner, A. J. G., Jöckel, P., Dameris, M., and Crutzen, P. J.: Will climate change increase ozone depletion from low-energy-electron precipitation?, Atmos. Chem. Phys., 10, 9647-9656, doi:10.5194/acp-10-9647-2010, 2010. [abstract, full text]

– New research article reports of an analysis of the seasonal oscillation in USA surface temperatures. They got a surprising result: “We found the presence of an orbit-climate relationship on time scales remarkably shorter than the Milankovitch period {relat…ed to the nutational forcing}. The relationship manifests itself through occasional destabilization of the phase of the seasonal component due to the local changing of balance between direct insolation and the net energy received by the Earth. Quite surprisingly, we found that the local intermittent dynamics is modulated by a periodic component of about 18.6 yr due to the nutation of the Earth, which represents the main modulation of the Earth’s precession.” It has an effect to Earth seasons: “The global effect in the last century results in a cumulative phase-shift of about 1.74 days towards earlier seasons, in agreement with the phase shift expected from the Earth’s precession.”
Citation: Vecchio, A., Capparelli, V., and Carbone, V.: The complex dynamics of the seasonal component of USA’s surface temperature, Atmos. Chem. Phys., 10, 9657-9665, doi:10.5194/acp-10-9657-2010, 2010. [abstract, full text]

– Measurements of carbon related parameters from the ocean in Canary islands. “We have evaluated the ESTOC (European Station for Time series in the Ocean at the Canary islands) observations of measured pH (total scale at 25 °C) and total alkalinity plus computed total dissolved inorganic carbon concentration (C_T) from 1995 to 2004 for surface and deep waters, by following all changes in response to increasing atmospheric carbon dioxide. The observed values for the surface partial pressure of CO₂ from 1995 to 2008 were also taken into consideration.” Results: “C_T at constant salinity, NC_T, increased at a rate of 0.85 μmol kg⁻¹ yr⁻¹ in the mixed layer, linked to an fCO₂ increase of 1.7±0.7 μatm yr⁻¹ in both the atmosphere and the ocean. Consequently, the mixed layer at ESTOC site has also become more acidic, −0.0017±0.0003 units yr⁻¹, whereas the carbonate ion concentrations and CaCO₃ saturation states have also decreased over time. NCT increases at a rate of 0.53, 0.49 and 0.40 μmol kg⁻¹ yr⁻¹ at 300, 600, and 1000 m, respectively.” and: “The total column inventory of anthropogenic CO₂ for the decade was 66±3 mol m⁻². A model fitting indicated that the column inventory of C_ANT increased from 61.7 mol m⁻² in the year 1994 to 70.2 mol m⁻² in 2004.”
Citation: González-Dávila, M., Santana-Casiano, J. M., Rueda, M. J., and Llinás, O.: The water column distribution of carbonate system variables at the ESTOC site from 1995 to 2004, Biogeosciences, 7, 3067-3081, doi:10.5194/bg-7-3067-2010, 2010. [abstract, full text]

– Addition of new fully automatic ground-based FTIR system for GHG total column measurements in tropics. There’s no Earth-shattering news here, but I just wanted to use this new research article to highlight one method to measure GHG-concentrations in the atmosphere. This new system uses Fourier Transform Spectrometer (FTIR) to measure effects of greenhouse gases to solar radiation. The incoming sunlight has energy also in infrared portion of the electromagnetic spectrum. Greenhouse gases have characteristic absorption lines in infrared so their effect can be measured from direct sunlight with proper instruments. The research article explains it further: “From the difference of the known solar spectrum from space and the measured solar spectrum after passing through the atmosphere, the total column of gases like CO₂, CH₄ and many others can be calculated.” The total column calculation additionally needs knowledge of the total dry air column which “can be derived either from surface pressure or from the measured O₂ total column”. The point of this study is to introduce a new measurement system which will be installed to the tropics where existing measurement network has been sparse. “First results of total column measurements at Jena, Germany show that the instrument works well and can provide parts of the diurnal as well as seasonal cycle for CO₂.”
Citation: Rayner, P. J., M. R. Raupach, M. Paget, P. Peylin, and E. Koffi (2010), A new global gridded data set of CO₂ emissions from fossil fuel combustion: Methodology and evaluation, J. Geophys. Res., 115, D19306, doi:10.1029/2009JD013439. [abstract, full text]

Papers on convection and climate

This is a list of papers on the convection and the climate. 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): Cunnington & Mitchell (1989) added.

Will moist convection be stronger in a warmer climate? – Del Genio et al. (2007) “The intensity of moist convection is an important diagnostic of climate change not currently predicted by most climate models. We show that a simple estimate of the vertical velocity of convective updrafts in a global climate model reproduces observed land-ocean differences in convective intensity. Changes in convective intensity in a doubled CO2 simulation are small because the tropical lapse rate tends to follow a moist adiabatic profile. However, updrafts strengthen by ∼1 m s−1 with warming in the lightning-producing regions of continental convective storms, primarily due to an upward shift in the freezing level. For the western United States, drying in the warmer climate reduces the frequency of lightning-producing storms that initiate forest fires, but the strongest storms occur 26% more often. For the central-eastern United States, stronger updrafts combined with weaker wind shear suggest little change in severe storm occurrence with warming, but the most severe storms occur more often.” Del Genio, A. D., M.-S. Yao, and J. Jonas (2007), Geophys. Res. Lett., 34, L16703, doi:10.1029/2007GL030525.

Impact Mechanisms of Shallow Cumulus Convection on Tropical Climate Dynamics – Neggers et al. (2007) “Subtropical shallow cumulus convection is shown to play an important role in tropical climate dynamics, in which convective mixing between the atmospheric boundary layer and the free troposphere initiates a chain of large-scale feedbacks. It is found that the presence of shallow convection in the subtropics helps set the width and intensity of oceanic ITCZs, a mechanism here termed the shallow cumulus humidity throttle because of the control exerted on the moisture supply to the deep convection zones. These conclusions are reached after investigations based on a tropical climate model of intermediate complexity, with sufficient vertical degrees of freedom to capture (i) the effects of shallow convection on the boundary layer moisture budget and (ii) the dependency of deep convection on the free-tropospheric humidity. An explicit shallow cumulus mixing time scale in this simple parameterization is varied to assess sensitivity, with moist static energy budget analysis aiding to identify how the local effect of shallow convection is balanced globally. A reduction in the mixing efficiency of shallow convection leads to a more humid atmospheric mixed layer, and less surface evaporation, with a drier free troposphere outside of the convecting zones. Advection of drier free-tropospheric air from the subtropics by transients such as dry intrusions, as well as by mean inflow, causes a substantial narrowing of the convection zones by inhibition of deep convection at their margins. In the tropical mean, the reduction of convection by this narrowing more than compensates for the reduction in surface evaporation. Balance is established via a substantial decrease in tropospheric temperatures throughout the Tropics, associated with the reduction in convective heating. The temperature response—and associated radiative contribution to the net flux into the column—have broad spatial scales, while the reduction of surface evaporation is concentrated outside of the convecting zones. This results in differential net flux across the convecting zone, in a sense that acts to destabilize those areas that do convect. This results in stronger large-scale convergence and more intense convection within a narrower area. Finally, mixed layer ocean experiments show that in a coupled ocean–atmosphere system this indirect feedback mechanism can lead to SST differences up to +2 K between cases with different shallow cumulus mixing time, tending to counteract the direct radiative impact of low subtropical clouds on SST.” Neggers, Roel A. J., J. David Neelin, Bjorn Stevens, 2007, J. Climate, 20, 2623–2642, doi: 10.1175/JCLI4079.1. [Full text]

The LMDZ4 general circulation model: climate performance and sensitivity to parametrized physics with emphasis on tropical convection – Hourdin et al. (2006) “The LMDZ4 general circulation model is the atmospheric component of the IPSL–CM4 coupled model which has been used to perform climate change simulations for the 4th IPCC assessment report. The main aspects of the model climatology (forced by observed sea surface temperature) are documented here, as well as the major improvements with respect to the previous versions, which mainly come form the parametrization of tropical convection. A methodology is proposed to help analyse the sensitivity of the tropical Hadley–Walker circulation to the parametrization of cumulus convection and clouds. The tropical circulation is characterized using scalar potentials associated with the horizontal wind and horizontal transport of geopotential (the Laplacian of which is proportional to the total vertical momentum in the atmospheric column). The effect of parametrized physics is analysed in a regime sorted framework using the vertical velocity at 500 hPa as a proxy for large scale vertical motion. Compared to Tiedtke’s convection scheme, used in previous versions, the Emanuel’s scheme improves the representation of the Hadley–Walker circulation, with a relatively stronger and deeper large scale vertical ascent over tropical continents, and suppresses the marked patterns of concentrated rainfall over oceans. Thanks to the regime sorted analyses, these differences are attributed to intrinsic differences in the vertical distribution of convective heating, and to the lack of self-inhibition by precipitating downdraughts in Tiedtke’s parametrization. Both the convection and cloud schemes are shown to control the relative importance of large scale convection over land and ocean, an important point for the behaviour of the coupled model.” Frédéric Hourdin, Ionela Musat, Sandrine Bony, Pascale Braconnot, Francis Codron, Jean-Louis Dufresne, Laurent Fairhead, Marie-Angèle Filiberti, Pierre Friedlingstein and Jean-Yves Grandpeix, et al., Climate Dynamics, Volume 27, Numbers 7-8, 787-813, DOI: 10.1007/s00382-006-0158-0. [Full text]

Influence of convective transport on tropospheric ozone and its precursors in a chemistry-climate model – Doherty et al. (2005) “The impact of convection on tropospheric O3 and its precursors has been examined in a coupled chemistry-climate model. There are two ways that convection affects O3. First, convection affects O3 by vertical mixing of O3 itself. Convection lifts lower tropospheric air to regions where the O3 lifetime is longer, whilst mass-balance subsidence mixes O3-rich upper tropospheric (UT) air downwards to regions where the O3 lifetime is shorter. This tends to decrease UT O3 and the overall tropospheric column of O3. Secondly, convection affects O3 by vertical mixing of O3 precursors. This affects O3 chemical production and destruction. Convection transports isoprene and its degradation products to the UT where they interact with lightning NOx to produce PAN, at the expense of NOx. In our model, we find that convection reduces UT NOx through this mechanism; convective down-mixing also flattens our imposed profile of lightning emissions, further reducing UT NOx. Over tropical land, which has large lightning NOx emissions in the UT, we find convective lofting of NOx from surface sources appears relatively unimportant. Despite UT NOx decreases, UT O3 production increases as a result of UT HOx increases driven by isoprene oxidation chemistry. However, UT O3 tends to decrease, as the effect of convective overturning of O3 itself dominates over changes in O3 chemistry. Convective transport also reduces UT O3 in the mid-latitudes resulting in a 13% decrease in the global tropospheric O3 burden. These results contrast with an earlier study that uses a model of similar chemical complexity. Differences in convection schemes as well as chemistry schemes ? in particular isoprene-driven changes are the most likely causes of such discrepancies. Further modelling studies are needed to constrain this uncertainty range.” Doherty, R. M., Stevenson, D. S., Collins, W. J., and Sanderson, M. G., Atmos. Chem. Phys., 5, 3205-3218, doi:10.5194/acp-5-3205-2005, 2005. [Full text]

Impacts of climate change and variability on tropospheric ozone and its precursors – Stevenson et al. (2005) “Two coupled climate-chemistry model experiments for the period 1990-2030 were conducted: one with a fixed climate and the other with a varying climate forced by the is92a scenario. By comparing results from these experiments we have attempted to identify changes and variations in physical climate that may have important influences upon tropospheric chemical composition. Climate variables considered include: temperature, humidity, convective mass fluxes, precipitation, and the large-scale circulation. Increases in humidity, directly related to increases in temperature, exert a major influence on the budgets of ozone and the hydroxyl radical: decreasing 03 and increasing OH. Warming enhances decomposition of PAN, releasing NOx, and increases the rate of methane oxidation. Surface warming enhances vegetation emissions of isoprene, an important ozone precursor. In the changed climate, tropical convection generally reduces, but penetrates to higher levels. Over northern continents, convection tends to increase. These changes in convection affect both vertical mixing and lightning NOx emissions. We find no global trend in lightning emissions, but significant changes in its distribution. Changes in precipitation and the large-scale circulation are less important for composition, at least in these experiments. Higher levels of the oxidants OH and H202 lead to increases in aerosol formation and concentrations. These results indicate that climate-chemistry feedbacks are dominantly negative (less 03, a shorter CH4 lifetime, and more aerosol). The major mode of inter-annual variability in the is92a climate experiment is ENSO. This strongly modulates isoprene emissions from vegetation via tropical land surface temperatures. ENSO is also clearly the dominant source of variability in tropical column ozone, mainly through changes in the distribution of convection. The magnitude of inter-annual variability in ozone is comparable to the changes brought about by emissions and climate changes between the 1990s and 2020s, suggesting that it will be difficult to disentangle the different components of near-future changes.” Stevenson D, Doherty R, Sanderson M, Johnson C, Collins B, Derwent D., Faraday Discuss. 2005;130:41-57; discussion 125-51, 519-24. [Full text]

Effect of convection on the summertime extratropical lower stratosphere – Dessler & Sherwood (2004) “Satellite and in situ water vapor and ozone observations near the base of the overworld ( ≈ 380-K potential temperature) are examined in summertime northern midlatitudes, with a focus on how their horizontal variations are influenced by deep convection. We show that summertime convection has a significant effect on the water vapor budget here, but only a small effect on the ozone budget. Using a simple model, we estimate that convection increases model extratropical water vapor at 380 K by 40% but decreases model extratropical ozone by only a few percent, relative to what would occur without convection. In situ data show that this convective injection occurs up to at least ∼390 K. This raises the possibility that the convectively moistened air might travel isentropically to the tropics and ascend into the stratospheric overworld without passing through the cold point. We argue that trends in convective moistening should be examined as possible contributors to observed trends in lower stratospheric water vapor, at least during summer months.” Dessler, A. E., and S. C. Sherwood (2004), J. Geophys. Res., 109, D23301, doi:10.1029/2004JD005209. [Full text]

Comparison between archived and off-line diagnosed convective mass fluxes in the chemistry transport model TM3 – Olivié et al. (2004) “The 40-year reanalysis data set ERA-40 from the European Centre for Medium-Range Weather Forecasts includes, unlike ERA-15, archived convective mass fluxes. These convective fluxes are useful for off-line chemistry transport modeling. The impact of using these archived convective mass fluxes (based on a convective parameterization described in Gregory et al. [2000] ) instead of off-line diagnosed mass fluxes (based on a convective parameterization described in Tiedtke [1989] ) was investigated with the chemistry transport model TM3. At first sight the two types of mass fluxes look similar. However, some differences can be noted: the archived updrafts extend higher than the off-line diagnosed ones; they are also less intense below 500 hPa over sea. The archived downdrafts are much weaker than the off-line diagnosed downdrafts. With archived convective mass fluxes, we found slightly higher 222Rn concentrations in the boundary layer, lower 222Rn values in the free troposphere and significantly higher 222Rn values in the upper troposphere and lower stratosphere. The effect on tropospheric chemistry of using archived mass fluxes instead of diagnosed ones is an increase of NO x and O3 in the free troposphere, but a decrease in the upper troposphere. The differences amount to up to 20% for O3 in the zonal and seasonal mean. Our results thus underline the sensitivity of tropospheric ozone chemistry to the description of convective transport. Comparison with 222Rn observations shows that the archived convective mass fluxes give better agreement in the tropical upper troposphere. More comparisons to free tropospheric observations of 222Rn or another tracer of convective transport will be needed to unambiguously identify either of the convective data sets as optimal for use in chemistry transport models.” Olivié, D. J. L., P. F. J. van Velthoven, A. C. M. Beljaars, and H. M. Kelder (2004), Geophys. Res., 109, D11303, doi:10.1029/2003JD004036.

Effects of Moist Convection on Mesoscale Predictability – Zhang et al. (2003) “In a previous study by the authors, it was shown that the problematic numerical prediction of the 24–25 January 2000 snowstorm along the east coast of the United States was in some measure due to rapid error growth at scales below 500 km. In particular they found that moist processes were responsible for this strong initial-condition sensitivity of the 1–2-day prediction of mesoscale forecast aspects. In the present study they take a more systematic look at the processes by which small initial differences (“errors”) grow in those numerical forecasts. For initial errors restricted to scales below 100 km, results show that errors first grow as small-scale differences associated with moist convection, then spread upscale as their growth begins to slow. In the context of mesoscale numerical predictions with 30-km resolution, the initial growth is associated with nonlinearities in the convective parameterization (or in the explicit microphysical parameterizations, if no convective parameterization is used) and proceeds at a rate that increases as the initial error amplitude decreases. In higher-resolution (3.3 km) simulations, errors first grow as differences in the timing and position of individual convective cells. Amplification at that stage occurs on a timescale on the order of 1 h, comparable to that of moist convection. The errors in the convective-scale motions subsequently influence the development of meso- and larger-scale forecast aspects such as the position of the surface low and the distribution of precipitation, thus providing evidence that growth of initial errors from convective scales places an intrinsic limit on the predictability of larger scales.” Zhang, F., Chris Snyder, Richard Rotunno, 2003: Effects of Moist Convection on Mesoscale Predictability. J. Atmos. Sci., 60, 1173–1185. [Full text]

The balance of effects of deep convective mixing on tropospheric ozone – Lawrence et al. (2003) “The balance of effects that vertical transport associated with deep cumulus convection has on tropospheric O3 is discussed. We first show theoretically that convective mixing of O3 can substantially reduce its column mean lifetime over clean regions, while a much smaller increase is generally expected over polluted regions. The global chemistry-transport model MATCH-MPIC confirms this, computing a 6% decrease in the annual mean tropospheric O3 burden and a 7% decrease in its lifetime due to convective transport of O3 alone. We find, however, that the net effect of convective transport of all trace gases (O3 and precursors together) is a 12% increase in the tropospheric O3 burden. Thus, in contrast to previous literature, our results indicate that the enhanced O3 production due to precursor transport from polluted regions significantly outweighs the reduction in O3 lifetime due to mixing over clean regions.” Lawrence, M. G., R. von Kuhlmann, M. Salzmann, and P. J. Rasch (2003), Geophys. Res. Lett., 30(18), 1940, doi:10.1029/2003GL017644. [Full text]

Changes of tracer distributions in the doubled CO2 climate – Rind et al. (2001) “Changes in tracer distributions in the troposphere and stratosphere are calculated from a control and doubled CO2 climate simulation run with the Goddard Institute for Space Studies Global Climate Middle Atmosphere Model. Transport changes are assessed using seven on-line tracers. Results show that interhemispheric transport is reduced by 5% along with a reduction in the Hadley circulation. Tropical transport from the troposphere into the stratosphere increases by some 30% associated with an increase in the stratospheric subtropical residual circulation. The tropical pipe becomes significantly more leaky, and greater transport into the lowermost stratosphere in the subtropics appears to be occurring, possibly in conjunction with a poleward shift in wave energy convergences. An increase in the high-latitude lower stratosphere residual circulation reduces the stratospheric residence time of extratropical injections such as bomb 14C by 11%. Vertical mixing within the troposphere by convection increases, reducing low level concentrations of tracers. The Hadley cell change is affected by the latitudinal gradient of tropical warming. The high-latitude lower stratosphere residual circulation change depends on the latitudinal gradient of the extratropical warming. Increased penetrating convection to the upper troposphere and the intensified residual circulation in the tropical upper troposphere/lower stratosphere appear to be the most robust of these results, with a magnitude that depends upon the degree of tropical warming. The consequence of this circulation change is to increase trace gas concentrations in the stratosphere and to decrease them in the troposphere for those species that have tropospheric sources.” Rind, D., J. Lerner, and C. McLinden (2001), J. Geophys. Res., 106, 28,061–28,079, doi:10.1029/2001JD000439.

Trace gas transport and scavenging in PEM-Tropics B South Pacific Convergence Zone convection – Pickering et al. (2001) “Analysis of chemical transport on Flight 10 of the 1999 Pacific Exploratory Mission (PEM) Tropics B mission clarifies the role of the South Pacific Convergence Zone (SPCZ) in establishing ozone and other trace gas distributions in the southwestern tropical Pacific. The SPCZ is found to be a barrier to mixing in the lower troposphere but a mechanism for convective mixing of tropical boundary layer air from northeast of the SPCZ with upper tropospheric air arriving from the west. A two-dimensional cloudresolving model is used to quantify three critical processes in global and regional transport: convective mixing, lightning NOx production, and wet scavenging of soluble species. Very low NO and O3 tropical boundary layer air from the northeastern side of the SPCZ entered the convective updrafts and was transported to the upper troposphere where it mixed with subtropical upper tropospheric air containing much larger NO and O3 mixing ratios that had arrived from Australia. Aircraft observations show that very little NO appears to have been produced by electrical discharges within the SPCZ convection. We estimate that at least 90% of the HNO3 and H2O2 that would have been in upper tropospheric cloud outflow had been removed during transport through the cloud. Lesser percentages are estimated for less soluble species (e.g., <50% for CH3OOH). Net ozone production rates were decreased in the upper troposphere by ∼60% due to the upward transport and outflow of low-NO boundary layer air. However, this outflow mixed with much higher NO air parcels on the southwest edge of the cloud, and the mixture ultimately possessed a net ozone production potential intermediate between those of the air masses on either side of the SPCZ." Pickering, K. E., et al. (2001), J. Geophys. Res., 106, 32,591–32,602, doi:10.1029/2001JD000328.

Development and Evaluation of a Convection Scheme for Use in Climate Models – Emanuel & Rothman (1999) “Cumulus convection is a key process in controlling the water vapor content of the atmosphere, which is in turn the largest feedback mechanism for climate change in global climate models. Yet scant attention has been paid to designing convective representations that attempt to handle water vapor with fidelity, and even less to evaluating their performance. Here the authors attempt to address this deficiency by designing a representation of cumulus convection with close attention paid to convective water fluxes and by subjecting the scheme to rigorous tests using sounding array data. The authors maintain that such tests, in which a single-column model is forced by large-scale processes measured by or inferred from the sounding data, must be carried out over a period at least as long as the radiative-subsidence timescale—about 30 days—governing the water vapor adjustment time. The authors also argue that the observed forcing must be preconditioned to guarantee integral enthalpy conservation, else errors in the single-column prediction may be falsely attributed to convective schemes. Optimization of the new scheme’s parameters is performed using one month of data from the intensive flux array operating during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, with the aid of the adjoint of the linear tangent of the single-column model. Residual root-mean-square errors, after optimization, are about 15% in relative humidity and 1.8 K in temperature. It is difficult to reject the hypothesis that the residual errors are due to noise in the forcing. Evaluation of the convective scheme is performed using Global Atmospheric Researh Program Atlantic Tropical Experiment data. The performance of the scheme is compared to that of a few other schemes used in current climate models. It is also shown that a vertical resolution better than 50 mb in pressure is necessary for accurate prediction of atmospheric water vapor.” Emanuel, Kerry A., Marina Živković-Rothman, 1999, J. Atmos. Sci., 56, 1766–1782. [Full text]

Mean climate and transience in the tropics of the UGAMP GCM: Sensitivity to convective parametrization – Slingo et al. (1994) “The sensitivity of the UK Universities Global Atmospheric Modelling Programme (UGAMP) General Circulation Model (UGCM) to two very different approaches to convective parametrization is described. Comparison is made between a Kuo scheme, which is constrained by large-scale moisture convergence, and a convective-adjustment scheme, which relaxes to observed thermodynamic states. Results from 360-day integrations with perpetual January conditions are used to describe the model’s tropical time-mean climate and its variability. Both convection schemes give reasonable simulations of the time-mean climate, but the representation of the main modes of tropical variability is markedly different. The Kuo scheme has much weaker variance, confined to synoptic frequencies near 4 days, and a poor simulation of intraseasonal variability. In contrast, the convective-adjustment scheme has much more transient activity at ail time-scales. The various aspects of the two schemes which might explain this difference are discussed. The particular closure on moisture convergence used in this version of the Kuo scheme is identified as being inappropriate.” Julia Slingo1,*, Mike Blackburn, Alan Betts, Roger Brugge, Kevin Hodges, Brian Hoskins, Martin Miller, Lois Steenman-Clark, John Thuburn, Quarterly Journal of the Royal Meteorological Society, Volume 120, Issue 518, pages 881–922, July 1994 Part A.

A Scheme for Representing Cumulus Convection in Large-Scale Models – Emanuel (1991) “Observations of individual convective clouds reveal an extraordinary degree of inhomogeneity, with much of the vertical transport accomplished by subcloud-scale drafts. In view of these observations, a representation of moist convective transports for use in large-scale models is constructed, in which the fundamental entities are these subcloud-scale drafts rather than the clouds themselves. The transport by these small-scale drafts is idealized as follows. Air from the subcloud layer is lifted to each level i between cloud base and the level of neutral buoyancy for undilute air. A fraction (ϵi) of the condensed water is then converted to precipitation, which falls and partially or completely evaporates in an unsaturated downdraft. The remaining cloudy air is then assumed to form a uniform spectrum of mixtures with environmental air at level i; these mixtures ascend or descend according to their buoyancy. The updraft mass fluxes Mi are represented as vertical velocities determined by the amount of convective available potential energy for undilute ascent to level i, multiplied by fractional areas σi, which are in turn determined in such a way as to drive the mass fluxes toward a state of quasi-equilibrium with the large-scale forcing. The downdraft mass fluxes are unique functions of the Mi, so that determination of the Mi closes the System. The main closure parameters in this scheme are the parcel precipitation efficiencies, ϵi, which determine the fraction of condensed water in a parcel lifted to level i that is converted to precipitation, and the fraction σis of precipitation that falls through unsaturated air. These may be specified as functions of altitude, temperature, adiabatic water content, and so on, and are regarded as explicitly determined by cloud microphysical processes. Specification of these parameters determines the vertical profiles of heating and moistening by cloud processes, given the large-scale (explicitly resolved) forcing. It is argued here that accurate calculation of the moistening by cumulus clouds cannot proceed without addressing the microphysics of precipitation formation, fallout, and reevaporation. One-dimensional radiative-convective equilibrium experiment with this scheme produce reasonable profiles of buoyancy and relative humidity. When large-scale descent is imposed, a trade-cumulus regime is produced, including a trade inversion and mixing-line structure in the cloud layer.” Emanuel, Kerry A., 1991, J. Atmos. Sci., 48, 2313–2329. [Full text]

On the dependence of climate sensitivity on convective parametrization – Cunnington & Mitchell (1989) “Two sensitivity experiments, in which CO2 is doubled and sea-surface temperatures are enhanced, were carried out using a general circulation model to determine the influence of the convective parametrization on simulated climate change. In the first experiment, a non-penetrative layer-swapping convection scheme is used; in the second, a penetrative scheme is used. It is found that the penetrative scheme gives the greater upper tropospheric warming (over 4.5 K compared to 4 K) and the greater reduction in upper tropospheric cloud, consistent with recent CO2 sensitivity studies. However, there is a 0.7 Wm–2 greater increase in net downward radiation at the top of the atmosphere in the experiment with the non-penetrative scheme, implying a larger tropical warming which is inconsistent with recent CO2 studies. Other possible explanations for discrepancies between recent studies of the equilibrium climate response to increasing CO2 are considered and discussed. The changes in the atmospheric fluxes of heat and moisture from the tropical continents in the model with the penetrative scheme differ from those found using the non-penetrative scheme, and those in an equilibrium experiment using the penetrative scheme. Thus, changes in circulation may explain the apparent discrepancy in the current experiments, but prescribed sea-surface temperature experiments may not provide a reliable indication of a model’s equilibrium climate sensitivity.” W M Cunnington and J F B Mitchell, Climate Dynamics, 1989, Volume 4, Number 2, 85-93, DOI: 10.1007/BF00208904.

A Comprehensive Mass Flux Scheme for Cumulus Parameterization in Large-Scale Models – Tiedtke (1989) “Observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large-scale models, but this approach, through the introduction of a spectral cloud ensemble, leads normally to rather complex schemes. In this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions. This is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection (GATE, Marshall Islands), tradewind cumuli (ATEX, BOMEX) and extratropical organized convection (SESAME-79) and then in a NWP model. The scheme considers a population of clouds where the cloud ensemble is described by a one-dimensional bulk model as earlier applied by Yanai et al. in a diagnostic study of tropical convection. Cumulus scale downdrafts are included. Various types of convection are represented, i.e., penetrative convection in connection with large-scale convergent flow, shallow convection in suppressed conditions like tradewind cumuli and midlevel convection like extratropical organized convection associated with potentially unstable air above the boundary layer and large-scale ascent. The closure assumptions for determining the bulk cloud mass flux are: penetrative convection and midlevel convection are maintained by large-scale moisture convergence and shallow convection by supply of moisture due to surface evaporation. The parameterization produces realistic fields of convective heating and appears to be in fair balance with real data for NWP as it does not initiate strong adjustment processes (spinup) in global form.” Tiedtke, M., 1989, Mon. Wea. Rev., 117, 1779–1800. [Full text]

Sea Surface Temperature, Surface Wind Divergence, and Convection over Tropical Oceans – Graham & Barnett (1987) “Large-scale convection over the warm tropical oceans provides an important portion of the driving energy for the general circulation of the atmosphere. Analysis of regional associations between ocean temperature, surface wind divergence, and convection produced two important results. First, over broad regions of the Indian and Pacific oceans, sea surface temperatures (SSTs) in excess of 27.5°C are required for large-scale deep convection to occur. However, SSTs above that temperature are not a sufficient condition for convection and further increases in SST appear to have little effect on the intensity of convection. Second, when SSTs are above 27.5°C, surface wind divergence is closely associated with the presence or absence of deep convection. Although this result could have been expected, it was also found that areas of persistent divergent surface flow coincide with regions where convection appears to be consistently suppressed even when SSTs are above 27.5°C. Thus changes in atmospheric stability caused by remotely forced changes in subsidence aloft may play a major role in regulating convection over warm tropical oceans.” N. E. Graham and T. P. Barnett, Science 30 October 1987: Vol. 238. no. 4827, pp. 657 – 659, DOI: 10.1126/science.238.4827.657.

Cassiope tetragona as thermometer

There are not much temperature series from Arctic and it also has been difficult to obtain reliable proxy based temperature reconstructions from the region. Recently published study has made a 131-year temperature reconstruction from Svalbard based on the changes in the annual growth of Cassiope tetragona.

Cassiope tetragona and its annual growth. Image: Callaghan et al. (1989).

Arctic regions have been estimated to be most affected by the climate change, and therefore it is important to have a good knowledge of the current and past climatic conditions in the region. There aren’t much temperature series from Arctic regions, and even the few series don’t extend very far to the past. There is a need for other accurate temperature indicators, which could also be used to interpret the past temperatures from the region. Here we encounter another problem. There aren’t really growing trees in the Arctic and smaller shrubs of the region tend to have very thin annual rings, which they don’t necessarily even produce every year. Thus, the annual tree-ring based methods are of no help in the problem.

In 1989 there was one method presented for determining temperatures from vegetation changes in the Arctic areas (Callaghan et al., 1989). The method is based on annual growth of Cassiope tetragona. Cassiope tetragona is an evergreen plant with white bell-shaped flowers and scale-like opposite leaves. Cassiope tetragona belongs to the heather plants. Cassiope tetragona is a perennial plant and is found in the arctic regions of Europe, North America, and Asia.

Cassiope tetragona grows a lot of leaves. It may have more than 230 in a twenty year old shoot. The leaves remain green for a long time and they do photosynthesis at least four years. Subsequently, leaves turn first yellow or red, and after couple of additional years they turn brown.

The new leaves of Cassiope tetragona are shorter in spring and autumn than in summer. This creates a wavy pattern which makes it possible to identify the growth of a single year and thus offers an opportunity to examine the association of the annual growth length and the number of new leaves to the climate.

Earlier studies have focused mainly on the details of the Cassiope tetragona annual growth association to the climate. These studies have shown that it is possible to use Cassiope tetragona for making temperature reconstructions. So far there’s not many actual temperature reconstructions based on Cassiope tetragona. Previous reconstructions have been up to hundred years in length (Rayback & Henry, 2006).

In a new study from Svalbard, a 131-year temperature reconstruction based on Cassiope tetragona annual growth was made (Weijers et al., 2010). The annual growth in length was measured from 32 plant samples. This resulted in a 169-year chronology of the annual growth length. This is the longest chronology so far, and the temperature reconstruction made from the chronology is also the longest so far.

The chronology’s connection to temperature and other climatic parameters was studied using different statistical methods. It turned out that the July temperature describes the annual growth length best. Behind that, other important climatic factors associated to the annual growth are the previous year’s precipitation in September and the average air temperature.

A reconstruction of July temperatures was made from the chronology. The reconstruction covered the period from 1876 to 2007. Reconstruction was calibrated with the measured temperatures from the region (which exist between 1912-2007). Reconstruction correlated quite well with the measured July temperature (R² = 0.34 for calibration period 1912-1959 and R² = 0.47 for the reference period 1960-2007). Temperature reconstruction together with the measured temperatures reveals that Svalbard has experienced significant warming after the year 1876. The amount of warming on average has been 0.07 degrees celsius per decade.

Temperature reconstructions from Cassiope tetragona thus appears to offer little relief to the sparseness of climatic data in the Arctic. Especially good aspects are the availability of Cassiope tetragona in the Arctic tundra also as fossilized, and the wide spread of Cassiope tetragona throughout the Arctic region. These factors together with good association between Cassiope tetragona annual growth and climate means that in the future we can expect to see temperature reconstructions reaching longer into the past and covering the entire Arctic vegetation region.

References:

Stef Weijers, Rob Broekman and Jelte Rozema, Quaternary Science Reviews, 2010, Dendrochronology in the High Arctic: July air temperatures reconstructed from annual shoot length growth of the circumarctic dwarf shrub Cassiope tetragona, doi:10.1016/j.quascirev.2010.09.003. [abstract]

T. V. Callaghan, B. A. Carlsson and N. J. C. Tyler, Journal of Ecology, Vol. 77, No. 3 (Sep., 1989), pp. 823-837. [abstract, full text]

Shelly A. Rayback, Gregory H. R. Henry, Reconstruction of Summer Temperature for a Canadian High Arctic Site from Retrospective Analysis of the Dwarf Shrub, Cassiope tetragona, Arctic, Antarctic, and Alpine Research, Volume 38, Number 2 / May 2006, Pages 228-238, DOI 10.1657/1523-0430(2006)38[228:ROSTFA]2.0.CO;2. [abstract]

See also my list of papers on Cassiope tetragona as a climate proxy

New research from last week 40/2010

I’ll start making weekly (hopefully) posts on the research published during the preceding week. I’m not including everything that was published but just some papers that got my attention. Those who follow my Facebook page (and/or Twitter) have already seen most of these, as I post these there as soon as I write them. Here, I’ll just put them out in one batch. Sometimes I might also point out to some other news as well, but the new research will be the focus here. By the way, if this sort of thing interests you, be sure to check out A Few Things Illconsidered, they have a weekly posting containing lots of links to new research and other climate related news.

Published last week:

– A new global fossil fuel CO2 emission data set. To me, especially interesting part is this: “We describe the use of ¹⁴CO₂ measurements to further constrain national emissions. Their value is greatest over large countries with heterogeneous emissions.”
Citation: Rayner, P. J., M. R. Raupach, M. Paget, P. Peylin, and E. Koffi (2010), A new global gridded data set of CO₂ emissions from fossil fuel combustion: Methodology and evaluation, J. Geophys. Res., 115, D19306, doi:10.1029/2009JD013439. [abstract]

– What happened the last time climate warmed suddenly in arctic Alaska? “Two episodes of extremely rapid floodplain alluviation occurred during the Pleistocene–Holocene transition, one between 14 and 12.8 cal ka BP and the other between 11.5 and 9.5 cal ka BP. These aggradation episodes coincided with periods of warming in summer when cottonwood (Populus balsamifera L.) expanded its range, peatlands became established, and widespread thermokarst occurred.”
Citation: Daniel H. Mann, Pamela Groves, Richard E. Reanier, and Michael L. Kunz, 2010, Floodplains, permafrost, cottonwood trees, and peat: What happened the last time climate warmed suddenly in arctic Alaska?, Quaternary Science Reviews, article in press, doi:10.1016/j.quascirev.2010.09.002. [abstract]

– A new study has made an effort to determine the effective number of climate models. 24 models were used in the study and it turned out that the effective number was far less. Amount of new information decreases when adding new models to the ensemble after the effective number. The effective number is 9 or 7.5 with two different methods. In tropics you need couple of models more.
Citation: Christopher Pennell and Thomas Reichler, On the Effective Number of Climate Models, Journal of Climate 2010, doi: 10.1175/2010JCLI3814.1. [abstract, full text]

– Graversen et al. have studied Greenland’s contribution to global sea level by the end of 21st century using an ice sheet model. Their result: “Greenland contributes 0–17 cm to global sea-level rise by the end of the 21st century. This range includes the uncertainties in climate-model projections, the uncertainty associated with scenarios of greenhouse-gas emissions, as well as the uncertainties in future outlet-glacier discharge. In addition, the range takes into account the uncertainty of the ice-sheet model and its boundary fields.”
Citation: Rune G. Graversen, Sybren Drijfhout, Wilco Hazeleger, Roderik van de Wal, Richard Bintanja and Michiel Helsen, Greenland’s contribution to global sea-level rise by the end of the 21st century,Climate Dynamics, DOI: 10.1007/s00382-010-0918-8. [abstract]

– New climate model results suggest that there was global climate reorganization going on during the medieval warm period: “We present results from a full-physics coupled climate model showing that a slight warming of the tropical Indian and western Pacific Oceans relative to the other tropical ocean basins can induce a broad range of the medieval circulation and climate changes indicated by proxy data, including many of those not explained by a cooler tropical Pacific alone.” NOTE: this is an open access paper so full text should be available in abstract page.
Citation: N. E. Graham, C. M. Ammann, D. Fleitmann, K. M. Cobb and J. Luterbacher, Support for global climate reorganization during the “Medieval Climate Anomaly”, Climate Dynamics, DOI: 10.1007/s00382-010-0914-z. [abstract]

– In a new study, a number of German winter tourism representatives were interviewed on their knowledge of climate change and its effect to their business. Some notes: “About half of the interviewees were not aware of the regional changes in natural snow conditions projected for the next 15–20 years. Nevertheless, the majority recognized climate change as a serious issue. Yet, stakeholders repeatedly emphasized their uncertainty about related scientific facts. They attributed their perception to mass media reports that suggest a lack of scientific consensus on climate change issues.”
Citation: Andreas Hoy, Stephanie Hänsel and Jörg Matschullat, How can winter tourism adapt to climate change in Saxony’s mountains?, Regional Environmental Change, DOI: 10.1007/s10113-010-0155-z. [abstract]

– Shindell et al. have studied how far spatially a local forcing influence extends. They used several models with a specific method they designed to simulate local aerosol and how far it affects surface temperature. In the extratropics the effects are difficult to see but in the tropics (roughly) they are clear: “Restricting the analysis to 30°S–60°N, where nearly all the forcing was applied, shows that forcing strongly influences response out to ∼4500 km away examining all directions. The meridional length of influence is somewhat shorter (∼3500 km or 30°), while it extends out to at least 12,000 km in the zonal direction.” While the models were quite different, they all showed similar responses in spatial effect.
Citation: Shindell, D., M. Schulz, Y. Ming, T. Takemura, G. Faluvegi, and V. Ramaswamy (2010), Spatial scales of climate response to inhomogeneous radiative forcing, J. Geophys. Res., 115, D19110, doi:10.1029/2010JD014108. [abstract]

Other news:

–

NODC ocean heat content update

Recently I wrote about NODC ocean heat content data pointing out couple of problematic issues there which seemed to indicate that claims of oceans cooling after 2003 (or 2004) based on NODC data are unfounded. The situation seems to be on hold and we better wait for data updates before making any claims on the situation after 2003.

Now NODC has published an update to their data. The resulting situation after early 2000’s doesn’t show cooling unless one wants to cherry-pick the 3-month averages starting from the high peak at about 2004.

Corrections are described here. Also the effects of the corrections to the previous version are shown (see especially page 10 of the PDF). In addition to remarkable difference in 2000’s, the warm episode between 1975 and 1985 has leveled off a bit. The general outlook is that the warming during recent decades seems now to proceed more smoothly than it did before.

On page 11 you can see how the differences arise mostly from the southern hemisphere. Page 13 shows that there has been large addition of temperature profiles in southern hemisphere between 2003 and 2004. There were almost 4000 profiles added back then and practically all of them were Argo floats. Page 14 shows new data additions after the previous data release.

There are three main themes in the corrections:

1. Data additions and quality control changes – including the Argo problems.
2. Changes in base climatology.
3. XBT bias corrections.

I’m not familiar enough with the second item to comment on it. There has been a steady flow of research articles on XBT biases – just this week there was Good (2010) published. Reading Good’s abstract makes me think that there might still be quite a lot to be done on XBT biases.

The item 1 is the one I wrote about previously. They say it includes NODC own corrections and also corrections from originators (including Argo). On Argo, they say:

Substantial quality control has been carried out by the Argo community on the profiling floats, mainly to correct pressure offsets.

Page 15 shows the changed data from Argo and from XBT’s since the last data release. There are quite a lot of the changed temperature profiles. The presentation of corrections ends with the question:

Are quality control differences related to Argo delayed-mode quality control, NODC handling of data, or both?

One thing I wonder is that are all the Argo corrections now done? Last time I checked the Argo website and they said they would be done by the end of 2010. So, does Argo website say anything new now? No, it doesn’t. It seems that either Argo hasn’t informed about their new status yet or they haven’t yet finished the corrections. So, considering that XBT corrections are also still coming in, we’ll just have to wait some more, situation is not yet clear.