Global Warming Science: An Annotated Bibliography
A summary of recent findings on the changing global climate.
Pumping Up the Volume
EIA, Emissions of Greenhouse Gases in the United States 2004
EIA, Annual Energy Outlook 2006
Global warming pollution emitted in the United States reached the highest level ever recorded in 2004, according to an Energy Information Administration (EIA) report released in December. This stands in stark contrast to the White House's assertion at the Montreal global warming talks just two weeks earlier that their voluntary policies were having a significant effect on emissions. Total emissions of heat-trapping gases grew by 139 million tons from 2003 to 2004, which represents a 2 percent increase. Transportation emissions grew by 3.1 percent, the largest jump since 1990. Overall 2004 emissions were 16 percent higher than just 15 years ago. Based on current policies, the EIA projects that these trends will only continue, leading to a further 38 percent increase in emissions by 2030.
Hotter and Hotter
J. Hansen et al., GISS Surface Temperature Analysis
(December 18, 2005)
World Meteorological Organization (WMO) Statement on the Status of the Global Climate in 2005
(December 15, 2005)
Global temperature data covering the meteorological year from December 2004 through November 2005 show 2005 tied with 1998 as the hottest year on record. The year 2005 continues the clear global warming trend of the last several decades by equaling the record warmth of 1998 without a boost from El Nino, which in 1998 added extra heat from the ocean to the earth's surface. The 10 warmest years on record have now all occurred since 1990.
C. Monnett, J.S. Gleason, and L.M. Rotterman. Presentation at the Society for Marine Mammalogy 16th Biennial Conference on the Biology of Marine Mammals
(December 12-16, 2005)
J. T. Overpeck, et al., EosEos 86, 309
(August 23, 2005)
National Snow and Ice Data Center press release
(September 28, 2005)
D.M. Lawrence and A.G. Slater, Geophysical Research Letters 32, L24401
(December 17, 2005)
A December 2005 report, drawn from aerial photographs taken in Alaska, showed that polar bears are literally drowning due to the loss of Arctic ice from global warming. Forced to swim long distances when the sea ice off the north coast of Alaska retreated a record 160 miles, at least four polar bears, and perhaps as many as 40, drowned in September 2004. Arctic ice retreat set another record in 2005, marking the fourth year in a row of record or near-record minimum Arctic sea ice extent, leading researchers at the National Snow and Ice Data Center and the University of Washington to conclude that "Arctic sea ice is likely on an accelerating, long-term decline." A comprehensive review by leading Arctic scientists concurred, finding that the Arctic is on a trajectory toward becoming ice-free in summer during this century. Permafrost on land is also melting at an alarming rate. New simulations that include permafrost dynamics in a global climate model project that with continued rapid growth of global warming pollution, two-thirds of the northern hemisphere's near-surface permafrost (to a depth of 11 feet) would melt by 2050 and more than 90 percent would melt by the end of the century.
- For more information: NSIDC press release
It's the Heat and the Humidity
B. Soden, et al., Science 310, 841
(November 4, 2005)
EIA, Annual Energy Outlook 2006
Water vapor traps more heat than any other constituent of the atmosphere. In contrast to carbon dioxide and other global warming pollutants, however, the amount of water vapor in the atmosphere is not significantly influenced by direct emissions from human sources. Rather, it is determined by the balance between evaporation from the earth's surface and rainfall. Recent satellite measurements confirm that this balance tends to keep global average relative humidity (the amount of water vapor in the atmosphere relative to the maximum amount it can hold) nearly constant. Because warmer air can hold more water, this implies that global warming results in an increase in the amount of heat trapped by water vapor, fueling additional warming. This constitutes a powerful positive feedback mechanism which approximately doubles the direct heating from adding carbon dioxide to the atmosphere, according to climate models.
Some global warming naysayers, most notably Richard Lindzen of the Massachusetts Institute of Technology, had questioned the water vapor feedback mechanism, speculating that atmospheric circulation patterns in the tropics could dry, rather than moisten, the upper troposphere. If this were true, a given increase in heat-trapping pollution would produce far less global warming than projected by current climate models. Lindzen's tropospheric drying hypothesis, however, is clearly rejected by the study made by Brian Soden of the University of Miami and colleagues at the University of Colorado, Princeton and the National Oceanic and Atmospheric Administration (NOAA). Using satellite measurements of infrared radiation originating from water vapor in the upper troposphere, these researchers found that the amount of water vapor in that critical zone increased between 1982 and 2004, in accordance with climate model simulations. The results are consistent with constant relative humidity and inconsistent with Lindzen's suggestion of upper tropospheric drying. This finding eliminates what was perhaps the most fundamental challenge to mainstream global warming projections.
The Core of the Problem
U. Siegenthaler et al., Science 310, 1313
(November 25, 2005)
Air bubbles trapped in Greenland and Antarctic ice sheets provide the most detailed record of the composition of the earth's atmosphere going back thousands of years. New results from the European ice coring project in Antarctica extend the record back to 650,000 years before the present and confirm that the current atmospheric carbon dioxide concentration of 380 parts per million (ppm) is much higher than anything on record. The relative abundance of different oxygen isotopes in the ice also provides a global temperature indicator. These data reveal that temperature and CO2 concentrations have been closely coupled during the entire period, with CO2 concentrations averaging 180 ppm during ice ages and 260 ppm to 280 ppm during warmer interglacial periods. The CO2 concentration never exceeded 300 ppm until humans began burning billions of tons of fossil fuels.
- For more information: Science Magazine, article abstract
Putting a Fine Point on Climate Extremes
Diffenbaugh et al., Proceedings of the National Academy of Sciences 102, 15774
(November 1, 2005)
Global warming projections are usually described in terms of increases in global mean temperature, but the largest impacts may come from extreme events, such as severe storms, heat waves and droughts. By their very nature, extreme events are hard to study and predict precisely because they are relatively rare and because they can be influenced by local factors, such as terrain and snow pack. New research by scientists at Purdue University and the Abdus Salam International Center for Theoretical Physics overcomes some of these challenges by using a high resolution regional model driven by large scale conditions calculated by a global model. This approach allowed the scientists to double both the resolution and the time period of their simulation compared with previous studies. All parts of the United States would experience at least a doubling in the frequency of extremely hot days (defined as hotter than 95 percent of days in the current climate), with the Southwest being particularly hard hit with up to 100 additional extremely hot days each year. The frequency of extremely wet days would also increase, with the Pacific Northwest expected to see the largest effect. Unfortunately, the increase in heavy rains would not necessarily make more water available for hydropower or irrigation because natural and engineered reservoirs are often overwhelmed by severe storms. Moreover, both the Northwest and the Gulf Coast would also see an increase in the number of dry days, giving truth to the old adage: When it rains, it pours.
- For more information: PNAS website, article abstract
More Players on the Hockey Team
E. R. Wahl and C.M. Ammann, Robustness of the Mann, Bradley, Hughes Reconstruction of Surface Temperatures: Examination of Criticisms Based on the Nature and Processing of Proxy Climate Evidence, Climate Change
New reconstructions of the earth's temperature for the last 1000 years confirm that the last several decades are most likely the warmest such period not just of the last century, but of the entire millennium. Thermometer readings with adequate global coverage are only available for about the last 150 years, so scientists have to rely on "proxy" records, such as tree rings, ice cores, and the distribution of plant pollen, to extrapolate back in time. This is accomplished using complicated statistical techniques, with increasing uncertainty the further back you go. Nonetheless, several independent groups of researches have reached similar conclusions. Their results resemble a hockey stick with the blade pointing up and to the right -- in other words, global temperatures were relatively steady for about 900 years and then turned up sharply during the 20th Century (see figure). This strongly reinforces the conclusion from other evidence (see, e.g., "smoking gun" above) that recent global warming is due to heat-trapping pollution.
Global warming naysayers, however, have singled out one analysis -- that of Mann, Bradley and Hughes, 1998 -- for attack. They claim that these researchers made statistical errors and inappropriately excluded certain data from their analysis. The charges were repeated in the Wall Street Journal and in a letter to the researchers from Joe Barton, Chairman of the powerful House Energy and Commerce Committee. Barton's letter reads more like an inquisition than an open minded investigation, and objections have been registered by the President of the National Academy of Sciences, the Executive Director of the American Association for the Advancement of Science, and Barton's Republican colleague Sherwood Boehlert, Chairman of the House Science Committee, among others. Most importantly, Mann et al.'s findings have recently been validated -- and those of their critics rejected -- by scientists at the National Center for Atmospheric Research. It remains to be seen whether naysayers will continue to face off against the hockey team or aim at a new target.
- For more information: The National Center for Atmospheric Research and the UCAR Office of Programs
Satellite and Surface Temperature Records Reconciled
C.A. Mears and F.J. Wentz, Science
(August 11, 2005)
A. Revkin, "Errors Cited in Assessing Climate Data," New York Times
(August 12, 2005)
A puzzling discrepancy among different approaches to measuring global warming was resolved when scientists discovered an error in previous calculations used to correct satellite temperature readings. Global warming naysayers had long pointed to satellite-based temperature measurements published by two scientists at the University of Alabama as evidence that there was great uncertainty about global warming. These measurements appeared to show that the earth's atmosphere was warming far more slowly than the earth's surface, contrary to the expectations of climate scientists and the predictions of climate models used to forecast the effects of increases in heat-trapping pollution. Scientists at Remote Sensing Systems reanalyzed the raw satellite data and found that the lower atmosphere is actually warming slightly faster than the surface, in agreement with theory and models. These scientists found that the previous analysis of the satellite data had inaccurately corrected for changes in the satellites' measurement time resulting from the decay of their orbit. The diurnal temperature cycle of warmer temperatures during the day and cooler temperatures at night means that a gradual change in measurement time introduces a spurious temperature trend that must be removed from the data. The University of Alabama scientists have now acknowledged that they made a mistake and have adjusted their data series, making it much more in line with other results.
- For more information: Science Magazine
Warm Seas Fuel More Destructive Storms
K. Emanuel, Nature (online)
(July 31, 2005)
P. Webster et al., Science 309: 1844;
(September 16, 2005)
An eerily prophetic paper, published one month before Hurricane Katrina slammed into the Gulf Coast, found that the destructive power of hurricanes is increasing along with ocean temperatures. Climate models predict that global warming will make hurricanes stronger, but most studies of the hurricane record do not reveal a clear pattern. A new analysis by hurricane expert Kerry Emanuel of MIT, however, found that a measure of the total destructive potential of hurricanes has increased markedly during the last 30 years. Emanuel combined information on storm duration with wind speed records to calculate the "power dissipation index." This index is strongly correlated with sea surface temperatures and has nearly doubled during the last 30 years in the Atlantic and Pacific basins. While natural cycles in the pattern of ocean circulation likely played a role, Emanuel attributes at least part of the increase to global warming.
Peter Webster and colleagues at the Georgia Institute of Technology and the National Center for Atmospheric Research reached a similar conclusion when they independently examined the intensity of hurricanes in the Atlantic, Pacific and Indian oceans over the last 35 years. These researchers also did not see a trend in the total number of hurricanes or tropical storms, but they did see a dramatic rise in the number of the most severe category 4 and 5 storms. Both the total number of these extremely dangerous storms and the percentage of total storms in these categories increased in every ocean basin. The total number of such storms jumped from 171 in the period from 1975 to 1989, to 269 storms between 1990 and 2004; at the same time the proportion of storms in the strongest categories went from 20 percent to 35 percent.
Science Academies Call for Prompt Action
(June 7, 2005)
In the run up to the Gleneagles G8 Summit in early July 2005, 11 national science academies (all G8 nations plus China, India and Brazil) stated that "The scientific understanding of climate change is now sufficiently clear to justify nations taking prompt action." The statement on global warming called on world leaders to acknowledge that the threat of climate change is clear and increasing, to recognize that delayed action will increase the risk of adverse effects and likely increase costs, to identify cost-effective steps that can be implemented to substantially reduce global greenhouse gas emissions, to develop and deploy clean energy technologies along with approaches to energy efficiency, and to work with developing nations to enable them to develop innovative solutions for mitigating and adapting to climate change.
- For more information: Joint science academies' statement
Ocean Warming -- The Smoking Gun of Global Warming
J. Hansen et al., Science 2005 308:1431;
(April 28, 2005)
T.P. Barnett et al., Science 2005 309:284;
(June 2, 2005)
New precise measurements of the accumulation of heat in the earth's ocean confirm that heat-trapping pollution is the primary cause of global warming. Two research teams, led by scientists at the Scripps Institution for Oceanography and NASA's Goddard Institute for Space Studies, reached the same conclusion independently. Their measurements show that not only are the earth's land and ocean surfaces warming, but that the heating has penetrated more than 1,000 feet into the oceans' depth. These observations clear away any question of whether the warming trend seen in surface readings could be a spurious result of changes in land use and weather station locations. They can only be explained as the result of the thickening blanket of heat-trapping pollution in the atmosphere, which causes the earth to retain excess energy from the sun. The NASA group quantified this energy imbalance and found that it closely matched the imbalance predicted by their climate model. "This energy imbalance is the 'smoking gun' that we have been looking for" according to Jim Hansen, director of the NASA Goddard Institute for Space Studies and the lead author of one of the studies.
- For more information: Science Magazine
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