May 30, 2003 COLLEGE PARK, Md. -- Land use changes in the United States are responsible for a significant portion of the country's temperature increase over the past five decades, says a University of Maryland study published in this week's issue of the journal Nature. The findings suggest that land use changes are responsible for more of the rise in global temperatures than scientists previously had thought, say authors Eugenia Kalnay and Ming Cai, scientists in the university's department of meteorology.
Over the past century, the Earth has warmed by about 1 degree F (Fahrenheit) and scientists expect the average global temperature to increase an additional 2 to 6 degrees F over the next 100 years. These may seem like insignificant increases, but when small changes in the average temperature last for a long time, they can cause dramatic changes in the climate. At the peak of the last ice age, some 18,000 years ago, the average temperature was only 7 degrees F colder than today, and glaciers covered much of North America.
Most scientists think the global warming trend is largely the result of human activities, principally the emission of greenhouse gases from power plants, cars and other sources. Land use change, such as the conversion of undeveloped land to housing or agricultural use, has been seen as an important but much smaller factor in this trend. However, the findings of Kalnay and Cai may force a reassessment of the relative importance of these two factors.
"Our estimates are that land use changes in the United States since the 1960s resulted in a rise of over 0.2 degrees F <> in the mean surface temperature, an estimate twice as high as those of previous studies," said Kalnay, a professor of meteorology. "We expect to extend our study to obtain global results later this year, but these findings for the United States already suggest that land use changes may account for between 1/3 and 1/2 of the observed surface global warming."
"The larger effect found in this study is likely because our method covers all changes in land use. Previous methods for estimating the impact of land use change relied on measures -- population counts or satellite measures of light at night -- that only provide an indication of the affects of urbanization, but not of other changes in land use," said Kalnay, who prior to coming to Maryland led the development of ensemble forecasts and other modeling improvements at the National Weather Service that made possible accurate 3 and 5 day forecasts.
Kalnay and Cai estimated the impact of land-use effects in the United States over the past 50 years by comparing trends in surface temperature measurements taken at almost 2000 surface weather stations around the country with those from a satellite-and-weather-balloon-based set of data from the U.S. National Centers for Environmental Prediction and the National Center for Atmospheric Research.
The University of Maryland is a recognized leader in global climate and land cover change research, led by the Joint Global Change Research Institute http://www.globalchange.umd.edu/index.html, the Earth System Science Interdisciplinary Center http://www.essic.umd.edu/Institute the Global Land Cover Facility http://esip.umiacs.umd.edu/index.shtml, and the departments of meteorology http://www.atmos.umd.edu/ and geography http://geog.umd.edu/.
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