AGW Observer

Observations of anthropogenic global warming

New research from last week 2/2011

Posted by Ari Jokimäki on January 17, 2011

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 they are published. 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. Here’s the archive for the news of previous weeks. 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. Planet 3.0 also reports new research.

Published last week:

Cessation of emissions would cause increasing temperatures

Climate commitment in an uncertain world – Armour & Doe (2011) “Climate commitment—the warming that would still occur given no further human influence—is a fundamental metric for both science and policy. It informs us of the minimum climate change we face and, moreover, depends only on our knowledge of the natural climate system. Studies of the climate commitment due to CO2 find that global temperature would remain near current levels, or even decrease slightly, in the millennium following the cessation of emissions. However, this result overlooks the important role of the non-CO2 greenhouse gases and aerosols. This paper shows that global energetics require an immediate and significant warming following the cessation of emissions as aerosols are quickly washed from the atmosphere, and the large uncertainty in current aerosol radiative forcing implies a large uncertainty in the climate commitment. Fundamental constraints preclude Earth returning to pre-industrial temperatures for the indefinite future. These same constraints mean that observations are currently unable to eliminate the possibility that we are already beyond the point where the ultimate warming will exceed dangerous levels. Models produce a narrower range of climate commitment, but undersample observed forcing constraints.” Armour, K. C., and G. H. Roe (2011), Geophys. Res. Lett., 38, L01707, doi:10.1029/2010GL045850. [full text]

Iran’s temperatures have been increasing since the 1970s

Testing for long-term trends in climatic variables in Iran – Tabari et al. (2011) “Analysis of long-term climatic data sets is currently of unprecedented interest to the scientific community. In this study, the trends of the annual maximum (Tmax), minimum (Tmin) and mean (Tmean) air temperatures and precipitation (P) time series were examined in the west, south and southwest of Iran for the period 1966–2005. The magnitude of the climatic trends was derived from the slopes of the regression lines, and the statistical significance was determined by means of the Mann-Kendall, Mann-Whitney and Mann-Kendall rank statistic tests. Pre-whitening was used to eliminate the influence of serial correlation on the Mann-Kendall test. The results showed a warming trend in annual Tmean, Tmax and Tmin at the majority of the stations which mostly began in the 1970 s. On average, the magnitudes of the significant positive trends in annual Tmean, Tmax and Tmin were (+)0.412, (+)0.452 and (+)0.493 °C per decade, respectively. However, the variations of the P series were not uniform over the region and there were various patterns (increasing and decreasing trends).” Hossein Tabari, Behzad Shifteh Somee and Mehdi Rezaeian Zadeh, Atmospheric Research, doi:10.1016/j.atmosres.2011.01.005.

Is the East Antarctic ice sheet stable?

Is the East Antarctic ice sheet stable? – Pingree et al. (2011) “The Greenland and East and West Antarctic ice sheets are assessed as being the source of ice that produced an Eemian sea level 6 m higher than present sea level. The most probable source is total collapse of the West Antarctic Ice Sheet accompanied by partial collapse of the adjacent sector of the East Antarctic Ice Sheet in direct contact with the West Antarctic Ice Sheet. This conclusion is reached by applying a simple formula relating the “floating fraction” of ice along flowlines to ice height above the bed. Increasing the floating fraction lowered ice elevations enough to contribute up to 4.7 m to global sea level. Adding 3.3 m resulting from total collapse of the West Antarctic Ice Sheet accounts for the higher Eemian sea level. Partial gravitational collapse that produced the present ice drainage system of Amery Ice Shelf contributes 2.3 m to global sea level. These results cast doubt on the presumed stability of the East Antarctic Ice Sheet, but destabilizing mechanisms remain largely unknown. Possibilities include glacial surges and marine instabilities at the respective head and foot of ice streams.” Katherine Pingree, Max Lurie and Terence Hughes, Quaternary Research, doi:10.1016/j.yqres.2010.12.001.

Future changes in Tibetan Plateau forests

Assessing potential impacts of climatic change on subalpine forests on the eastern Tibetan Plateau – Xiaodan et al. (2011) “Forest gap models have been used widely in the study of forest dynamics, including predicting long-term succession patterns and assessing the potential impacts of climate change on forest structure and composition. However, little effort is devoted to predict forest dynamics in the high elevation areas, although they have the sensitive response to global climate change. In the present study, based on a modified height-diameter function, we developed a new version (FAREAST-GFSM) of the forest patch model, FAREAST for simulating the changes of subalpine forests. The observed data from the Gongga Mt. Alpine Station were also used to test model precision. With the improved performance of FAREAST-GFSM, we explored the impact of three warming scenarios on subalpine forest on the eastern Tibetan plateau within a 100-year period. The study result indicates that the effects of climate change were evident on subalpine forests in the high elevation areas. The response of different species to the warming climate might eventually transform the subalpine Abies fabric forest into Betula utilis forest similar to that which is now widely distributed in the eastern Tibetan Plateau mountainous areas with the relatively lower elevation. Subalpine forests could move to higher and colder areas, which are currently tundra.” Wang Xiaodan, Cheng Genwei and Zhong Xianghao, Climatic Change, DOI: 10.1007/s10584-010-0008-2.

Total solar irradiance value for solar minimum

A new, lower value of total solar irradiance: Evidence and climate significance – Kopp & Lean (2011) “The most accurate value of total solar irradiance during the 2008 solar minimum period is 1360.8 ± 0.5 W m−2 according to measurements from the Total Irradiance Monitor (TIM) on NASA’s Solar Radiation and Climate Experiment (SORCE) and a series of new radiometric laboratory tests. This value is significantly lower than the canonical value of 1365.4 ± 1.3 W m−2 established in the 1990s, which energy balance calculations and climate models currently use. Scattered light is a primary cause of the higher irradiance values measured by the earlier generation of solar radiometers in which the precision aperture defining the measured solar beam is located behind a larger, view-limiting aperture. In the TIM, the opposite order of these apertures precludes this spurious signal by limiting the light entering the instrument. We assess the accuracy and stability of irradiance measurements made since 1978 and the implications of instrument uncertainties and instabilities for climate research in comparison with the new TIM data. TIM’s lower solar irradiance value is not a change in the Sun’s output, whose variations it detects with stability comparable or superior to prior measurements; instead, its significance is in advancing the capability of monitoring solar irradiance variations on climate-relevant time scales and in improving estimates of Earth energy balance, which the Sun initiates.” Greg Kopp and Judith L. Lean, GEOPHYSICAL RESEARCH LETTERS, VOL. 38, L01706, 7 PP., 2011, doi:10.1029/2010GL045777.

Solar activity cycles in tree rings of Brazil

Sun-earth relationship inferred by tree growth rings in conifers from Severiano De Almeida, Southern Brazil – Prestes et al. (2011) “This study of Sun-Earth relationships is based on tree growth rings analysis of araucarias (Araucaria angustifolia) collected at Severiano de Almeida (RS) Brazil. A chronology of 359 years was obtained, and the classical method of spectral analysis by iterative regression and wavelet method was applied to find periodicities and trends contained in the tree growth. The analysis of the dendrochronological series indicates representative periods of solar activity of 11 (Schwabe cycle), 22 (Hale cycle), and 80 (Gleissberg cycle) years. The result shows the possible influence of the solar activity on tree growth in last the 350 years. Periods of 2 to 7 years were also found and could represent a response of the trees to local climatic conditions. Good agreement between the time series of tree growth rings and the 11 year solar cycle was found during the maximum solar activity periods.” A. Prestes, N.R. Rigozo, D.J.R. Nordemann, C.M. Wrasse, M.P. Souza Echer, E. Echer, M.B. da Rosa and P.H. Rampelotto, Journal of Atmospheric and Solar-Terrestrial Physics, doi:10.1016/j.jastp.2010.12.014.

Difficulty of finding cloud-free pixel with MODIS

Global analysis of cloud field coverage and radiative properties, using morphological methods and MODIS observations – Bar-Or et al. (2011) “The recently recognized continuous transition zone between detectable clouds and cloud-free atmosphere (“the twilight zone”) is affected by undetectable clouds and humidified aerosol. In this study, we suggest to distinguish cloud fields (including the detectable clouds and the surrounding twilight zone) from cloud-free areas, which are not affected by clouds. For this classification, a robust and simple-to-implement cloud field masking algorithm which uses only the spatial distribution of clouds, is presented in detail. A global analysis, estimating Earth’s cloud field coverage (50° S–50° N) for 28 July 2008, using the Moderate Resolution Imaging Spectroradiometer (MODIS) data, finds that while the declared cloud fraction is 51%, the global cloud field coverage reaches 88%. The results reveal the low likelihood for finding a cloud-free pixel and suggest that this likelihood may decrease as the pixel size becomes larger. A global latitudinal analysis of cloud fields finds that unlike oceans, which are more uniformly covered by cloud fields, land areas located under the subsidence zones of the Hadley cell (the desert belts), contain proper areas for investigating cloud-free atmosphere as there is 40–80% probability to detect clear sky over them. Usually these golden-pixels, with higher likelihood to be free of clouds, are over deserts. Independent global statistical analysis, using MODIS aerosol and cloud products, reveals a sharp exponential decay of the global mean aerosol optical depth (AOD) as a function of the distance from the nearest detectable cloud, both above ocean and land. Similar statistical analysis finds an exponential growth of mean aerosol fine-mode fraction (FMF) over oceans when the distance from the nearest cloud increases. A 30 km scale break clearly appears in several analyses here, suggesting this is a typical natural scale of cloud fields. This work shows different microphysical and optical properties of cloud fields, urging to separately investigate cloud fields and cloud-free atmosphere in future climate research.” Bar-Or, R. Z., Altaratz, O., and Koren, I., Atmos. Chem. Phys., 11, 191-200, doi:10.5194/acp-11-191-2011, 2011. [full text]

Differences in mountain flora survival across Europe

21st century climate change threatens mountain flora unequally across Europe – Engler et al. (2011) “Continental-scale assessments of 21st century global impacts of climate change on biodiversity have forecasted range contractions for many species. These coarse resolution studies are however of limited relevance for projecting risks to biodiversity in mountain systems, where pronounced microclimatic variation could allow species to persist locally, and are ill-suited for assessment of species-specific threat in particular regions. Here, we assess the impacts of climate change on 2632 plant species across all major European mountain ranges, using high-resolution (ca. 100 m) species samples and data expressing four future climate scenarios. Projected habitat loss is greater for species distributed at higher elevations; depending on the climate scenario, we find 36–55% of alpine species, 31–51% of subalpine species and 19–46% of montane species lose more than 80% of their suitable habitat by 2070–2100. While our high-resolution analyses consistently indicate marked levels of threat to cold-adapted mountain florae across Europe, they also reveal unequal distribution of this threat across the various mountain ranges. Impacts on florae from regions projected to undergo increased warming accompanied by decreased precipitation, such as the Pyrenees and the Eastern Austrian Alps, will likely be greater than on florae in regions where the increase in temperature is less pronounced and rainfall increases concomitantly, such as in the Norwegian Scandes and the Scottish Highlands. This suggests that change in precipitation, not only warming, plays an important role in determining the potential impacts of climate change on vegetation.” Robin Engler, Christophe F. Randin, Wilfried Thuiller, Stefan Dullinger, Niklaus E. Zimmermann, Miguel B. Araújo, Peter B. Pearman, Gwenaëlle Le Lay, Christian Piedallu, Cécile H. Albert, Philippe Choler, Gheorghe Coldea, Xavier De Lamo, Thomas Dirnböck, Jean-Claude Gégout, Daniel Gómez-García, John-Arvid Grytnes, Einar Heegaard, Fride Høistad, David Nogués-Bravo, Signe Normand, Mihai Puşcaş, Maria-Teresa Sebastiá, Angela Stanisci, Jean-Paul Theurillat, Mandar R. Trivedi, Pascal Vittoz, Antoine Guisan, Global Change Biology, DOI: 10.1111/j.1365-2486.2010.02393.x.

Growing season timing changes in Northern Hemisphere

Phenology shifts at start vs. end of growing season in temperate vegetation over the Northern Hemisphere for the period 1982–2008 – Jeong et al. (2011) “Changes in vegetative growing seasons are dominant indicators of the dynamic response of ecosystems to climate change. Therefore, knowledge of growing seasons over the past decades is essential to predict ecosystem changes. In this study, the long-term changes in the growing seasons of temperate vegetation over the Northern Hemisphere were examined by analyzing satellite-measured normalized difference vegetation index and reanalysis temperature during 1982–2008. Results showed that the length of the growing season (LOS) increased over the analysis period; however, the role of changes at the start of the growing season (SOS) and at the end of the growing season (EOS) differed depending on the time period. On a hemispheric scale, SOS advanced by 5.2 days in the early period (1982–1999) but advanced by only 0.2 days in the later period (2000–2008). EOS was delayed by 4.3 days in the early period, and it was further delayed by another 2.3 days in the later period. The difference between SOS and EOS in the later period was due to less warming during the preseason (Jan-Apr) before SOS compared to the magnitude of warming in the preseason (June-Sept) before EOS. At a regional scale, delayed EOS in later periods was shown. In North America, EOS was delayed by 8.1 days in the early period and delayed by another 1.3 days in the later period. In Europe, the delayed EOS by 8.2 days was more significant than the advanced SOS by 3.2 days in the later period. However, in East Asia, the overall increase in LOS during the early period was weakened in the later period. Admitting regional heterogeneity, changes in hemispheric features suggest that the longer-lasting vegetation growth in recent decades can be attributed to extended leaf senescence in autumn rather than earlier spring leaf-out.” Su-Jong Jeong, Chang-Hoi Ho, Hyeon-Ju Gim, Molly E. Brown, Global Change Biology, DOI: 10.1111/j.1365-2486.2011.02397.x.

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