Web Extra Monday, June 2

Land use could also affect climate

Scientists have traditionally called attention to heat-trapping greenhouse gases as a reason for climate change, commonly known as global warming. A new study in the 2003 Nature adds to evidence that urbanization and other land-use changes may play a comparable role in climate change.

A striking amount of the U.S. surface warming trend, about 40 percent, is likely due to land-use change rather than greenhouse gases, say authors Eugenia Kalnay and Ming Cai of the University of Maryland. Land-use change since the 1960s has caused a climb in mean surface temperature above 0.2 degrees Fahrenheit, double that of prior estimates. While this increase may appear insignificant, small temperature variations can cause large climatic changes.

The impacts of land-use and greenhouse gas on climate change have been hard to separate. In this study, Kalnay and Cai found a way to distinguish them. The scientists gauged 50 years of U.S. temperatures from nearly 2000 surface weather stations. "Surface station temperatures are affected by both greenhouse warming and land-use changes," Kalnay says. They also obtained data based on satellite and weather-balloon observations that are sensitive to greenhouse warming but not land use."We used the difference in the trends as an estimate of the impact of land-surface use changes."

Kalney adds that "this study does not deny in any way global warming [by greenhouse gases]." The researchers detected warming by gases in both surface station and satellite-balloon data. The land-use impact in this study may be larger than other estimates because all land-use changes were included, whereas earlier techniques were based on effects of urbanization such as population counts or satellite measures of light.

State climatologist Roger Pielke of Colorado State University applauds the study. "This is very important work, as it further documents the major role of land-use change on regional and global climate. It also provides an explanation for a significant portion of the observed surface temperature trends over the last century," he says. With a paper that appeared in the June 2002 Philosophical Transactions of the Royal Society of London, Pielke and colleagues proposed that land-use changes may rival greenhouse gases as a cause for climate change. "The heightened recognition of the role of urbanization and land-use change within the climate system makes climate prediction a much more difficult problem than previously thought."

The U.S. findings suggest that land-use changes may be responsible for much of the observed surface global warming. "We plan to apply the same methodology to the whole world, to different seasons, to other variables such as winds and humidity, and to use trends in satellite data to validate and interpret the changes that we observe with this method," Kalnay says.

Neeta Bijoor
Geotimes contributing writer


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