Why warming? Climate change confidential.

• Author: Bailey, Ronald
• Position: Citings

THE UNITED Nations Inter-governmental Panel on Climate Change claims to have found "new and stronger evidence that most of the observed warming over the last 50 years is attributable to human activities." This conclusion is based on improvements in computer models that can now "produce satisfactory simulations of the current climate." But two recent studies show that the models may not have adequately accounted for two important factors: soot and land use changes.

The first study, by University of Maryland climate researchers Eugenia Kalnay and Ming Cal, was published last May in Nature. It showed that, in addition to the well-known "urban heat island effect," in which temperatures increase in metropolitan areas, other land use changes, especially agricultural conversion and irrigation, cause surface warming as well. The authors wrote that "the trend in daily mean temperature due to land use changes is 0.35 degrees centigrade per century. "This value is more than twice as high as previous estimates based on urbanization alone.

The second study, by James Hansen and Larissa Nazarenko of NASA'S Goddard Institute for Space Studies, appeared in the December Proceedings of the National Academy of Sciences. Hansen and Nazarenko looked at the effect that the soot produced by burning fossil fuels and biomass has once it settles on ice and snow in the Northern Hemisphere. Dirty snow melts faster than clean snow because the black particles absorb more heat from the sun. Hansen and Nazarenko estimate that the soot effect may be responsible for about 0.2 degree...