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Media Contacts:
Dr. Vinod Saxena, 919/515-7290 or [email protected]
Tim Lucas, News Services, 919/515-3470 or [email protected]
Nov. 4, 1999
Study Finds Southeast's Climate Is in Slight Cooling Trend
FOR IMMEDIATE RELEASE
RALEIGH, N.C. -- Despite record-breaking heat this summer and increased levels of greenhouse gases in our air, the climate in the southeastern United States actually has cooled slightly over the past 50 years. North Carolina State University atmospheric scientists have found that annual mean daily temperatures at 52 weather stations across the region have decreased, on average, 0.10 degree Celsius -- or about 0.18 degree Fahrenheit -- from 1949 to 1994.
A drop that small may seem insignificant. But lead researcher Dr. Vinod Saxena says its implications may be huge as scientists and policy makers from around the world gather this month (November 1999) at a United Nations' Global Climate Conference in Argentina to debate the controversial Kyoto Treaty on carbon dioxide emissions and greenhouse warming.
"The bottom line is, despite a documented increase of carbon dioxide in our atmosphere, we found no evidence of greenhouse warming in the southeastern United States," Saxena says. Other studies have documented similar cooling trends in parts of Asia and Europe, he says.
"According to the global warming model the Kyoto Treaty is based on, these are regions where warming should be occurring. But it's not," he says. Such discrepancies should be a red flag to treaty ratification, he believes, because they show that though the causes and effects of greenhouse warming are well proven on a global scale, its regional effects aren't yet well understood.
Saxena and his colleagues at NC State have published their studies on the Southeast's climate in three peer-reviewed scientific papers. They presented their most recent findings at the American Meteorological Society's eighth Conference on Climate Variations in Denver, Colo., earlier this fall.
The Kyoto Treaty mandates cutting carbon dioxide emissions by 5 percent below 1990 levels as a way of slowing or reversing global warming. The Southeast's coal-fired power plants, coal mining and fossil fuel-related industries would likely be adversely affected by such reductions, Saxena says.
The main scientific problem with the model used as a basis for the treaty, he says, is that it takes into account the effects of carbon dioxide, but not of airborne particulate matter, also called aerosols. Aerosols are created by the same natural and manmade sources as greenhouse gases, including coal-fired power plants. But because they absorb water and deflect solar radiation, they have the same effect as painting a house roof white -- they reflect heat.
In regions like the Southeast -- which tends to be a catch basin for air pollution generated by industrial plants outside the region, in the Ohio Valley -- the sunlight-deflecting effects of aerosols in that pollution offsets the warming effects of its carbon dioxide content, Saxena says.
His studies of cloud cover at Mount Mitchell since 1986 show conclusively that clouds fed by dirty air masses -- created when airflow comes from the Ohio Valley -- are more reflective than clouds formed by air masses that come from cleaner environments such as the ocean or coastal plain. Cooling surface temperatures have coincided with the increase of aerosols in our air.
"I am not saying that it is good to have dirty air -- I have witnessed pollution so bad it produces clouds with an acidity that matches pure lemon juice and vinegar," Saxena says. "What I am saying is before we pass an international treaty that will cause severe economic dislocations in the Southeast, we should make sure we understand the regional causes and effects of carbon dioxide and the role of aerosols and cloud cover in heating and cooling. Scientific credibility, and thousands of jobs, are at stake."
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NOTE TO EDITORS: Abstracts from Dr. Vinod Saxena's most recent publications follow. For full texts, contact Saxena at [email protected], or Tim Lucas, News Services, at (919) 515-3470 or [email protected].
"Sulfate-induced Cooling in the Southeastern U.S.: An Observational Assessment" published Aug. 15, 1999 in Geophysical Research Letters, vol. 26, no. 16 by V.K. Saxena of NC State University and Surabi Menon, formerly on NC State and now at Columbia Univ.
Abstract: The effect of sulfates on cloud microphysical and optical properties have been studied using data from a rural mountaintop location in Mt. Mitchell State Park, North Carolina. Although the amended Clean Air Act has limited the sulfur emissions beginning in 1990, we found the sulfate concentrations greater during 1993-97 compared to that during 1986-89. Cloud albedo inferred from satellitedata and calculated from surface observations does not indicate a monotonic increase with increasing sulfates. The direct and indirect (cloud-mediated) sulfate forcing are assessed to be - 4.8 and -4 W m-2. These values exceed current model predictions as evaluated by other investigators. Surface temperature records of the region during 1949-94 indicate a cooling trend tacitly supporting our assessment.
"Climate Variations in the Southeastern U.S. During 1949-94: Did a Volcano Affect It During 1992-94?" presented at the American Meteorological Society's 8th Conference on Climate Variations, Sept. 13-17, 1999 by V.K. Saxena and Shaocai Yu of NC State University
Introduction: Stratospheric volcanic aerosols can scatter incoming solar radiation to space, increasing planetary albedo, reducing the total amount of solar energy reaching the troposphere and the earth's surface, decreasing the daytime maximum temperature (aerosol shortwave forcing). They can also absorb and scatter outgoing terrestrial longwave radiation, increasing the nighttime minimum surface temperature (longwave forcing). The southeastern U.S. has been recognized (IPCC, 1995) as a region where the effect of anthropogenic aerosols (NRC, 1996) supersedes that of manmade greenhouse gases and manifests itself in terms of cooling of the surface-air temperature (Boucher and Lohmann, 1995). The uncertainty in the magnitude of the estimated direct and cloud-mediated (also called the indirect effect) cooling effect of aerosols (Schwartz, 1996; Kiehl and Briegleb, 1993) is a major barrier for a reliable prediction of climate change on the scale of a decade and longer. The purpose of this
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