Higher hints of greenhouse effects.

Higher hints of greenhouse effects

Computer models predict that increasing concentrations of greenhouse gases should have contrasting effects on different portions of the atmosphere. These gases are expected to heat the lowest layer, or troposphere. But the next region up -- the stratosphere -- should cool. A new study of atmospheric temperatures in the Northern Hemisphere finds that tropospheric and stratospheric temperatures have indeed headed in different directions over the last 20 years.

David J. Karoly of Monash University in Melbourne, Australia, examined temperature measurements taken by balloons at 147 stations in the Northern Hemisphere from 1964 to 1985. While other researchers studying similar data have grouped stations in latitude bands, Karoly broke the hemisphere up into boxes based on latitude and longitude. He did this to separate areas with many stations from areas with sparse coverage such as Africa, East Europe and Asia. Of the 61 grid boxes, 13 boxes (21 percent) showed a statistically significant divergence between tropospheric and stratospheric temperatures, Karoly reports in the May GEOPHYSICAL RESEARCH LETTERS. In an earlier study he had shown that an even larger percentage of boxes in the Southern Hemisphere exhibited this divergence.

In some ways, says Karoly, these patterns are consistent with trends expected from the greenhouse effect. But he stresses that other factors, including ozone loss in the stratosphere, could cause the temperature changes he observed. Other scientists have reported that human-made chemicals are noticeably thinning the global ozone layer.