Jan. 14, 2000 A researcher from NASA's Marshall Space Flight Center in Huntsville, Ala., working with a team of American and British investigators at the behest of the U.S National Research Council, hopes a new joint study will shed additional light on the global warming phenomenon.
According to the report, "Reconciling Observations of Global Temperature Change," the reality of global warming is not disputed. Just how much global warming the Earth has experienced is the point of contention among many researchers, says Roy Spencer, senior NASA scientist for climate studies at the Global Hydrology and Climate Center in Huntsville. Estimates range from negligible change to a rise of 0.4 or 0.5 degrees Celsius over the last 20 years.
The report will be issued today at 9 a.m. PST, during the annual conference of the American Meteorological Society in Long Beach, Calif. Its purpose: to help resolve debate caused by differences between satellite measurements, which in the last 20 years have shown very little cumulative atmospheric warming, and surface-based measurements that have shown substantial warming during the same period.
Spencer and his Global Hydrology Center colleague John Christy, a professor of atmospheric sciences at the University of Alabama in Huntsville, have tracked global temperatures continuously for NASA since January 1979. Unlike ground-based studies, their measurements come from Earth-orbiting satellites that record minute thermal changes in the Earth's lower and middle troposphere, which extends from the planet's surface to roughly 6 miles above sea level. "Whereas climate models have predicted the layer should warm about 25 percent faster than the surface," Spencer says, "satellite studies have shown that warming of the lower and middle troposphere over the last 20 years has been substantially less than that measured at the surface." Those results have been corroborated by weather balloon data, he adds.
Spencer and Christy's first concern is the accuracy of their measurements, Spencer says, not the origin of global warming. They are not trying to refute existing studies, nor point to a definitive cause for the trend. Rather, it is their hope to provide a more comprehensive overview of the global situation, using the latest in space technology to augment ground-based measurements.
The evidence reviewed by the National Research Council panel led them to conclude that recorded differences between surface and upper air trends over the past two decades are "at least partially real," according to the report.
While the report does not attribute the surface warming to a particular cause, it does address possible reasons why the upper air may have warmed less rapidly than the surface. These reasons include both natural factors and human activities. The report also cites the susceptibility of surface- and satellite-based instruments and measuring techniques to some degree of error, leading to the disparate findings.
"The final consensus of the NRC study team is that satellite measurements do not refute the fact that surface temperatures have been rising," Spencer says. The study concludes that further research is needed to fully explain the differences between surface and tropospheric global warming trends.
"High-quality measurements are key to understanding this phenomenon," Spencer says. "It could take many more years of satellite-based and ground-based measurements before we can say just how much warming is the result of human activity as opposed to natural climate fluctuations."
The American Meteorological Society conference convened Sunday. It concludes Friday.
Members of the National Research Council's commission included researchers from the University of Washington in Seattle; NASA's Goddard Institute for Space Studies in New York, N.Y.; the National Center for Atmospheric Research in Boulder, Colo.; the National Oceanic and Atmospheric Administration's Air Resources Laboratory in Silver Spring, Md.; the National Climatic Data Center in Asheville, N.C.; the National Environmental Satellite, Data and Information Service in Camp Springs, Md.; the Lawrence Livermore National Laboratory in Livermore, Calif.; Remote Sensing Systems in Santa Rosa, Calif.; and the Hadley Centre for Climate Prediction and Research in Berkshire, U.K.
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