Human-caused damage to the ozone layer is messing with the weather in the Southern Hemisphere, according to new research.
Last year, atmospheric scientists David Thompson of Colorado State University, Fort Collins, and Susan Solomon of the National Oceanic and Atmospheric Administration in Boulder reported that in the Southern Hemisphere, winds in the troposphere--the part of the atmosphere closest to Earth--seemed to shift in synch with seasonal changes in the ozone layer, even though the ozone sits in the stratosphere, one layer up. The link prompted them to propose that seasonal thinning of the ozone layer was affecting the weather far below, and that it was at least partly responsible for observed cooling of Antarctica and a slight warming of the Antarctic peninsula (Science, 3 May 2002).
Now Thompson and climate scientist Nathan Gillett of the University of Victoria in British Columbia have used a computer model to test whether the human-caused ozone depletion was really wreaking havoc with Antarctica's weather. They ran the model once using estimates of preindustrial ozone concentrations and then again with the lower levels we see today, keeping everything else the same. The climate simulation predicted exactly what they saw in late spring and summer: stronger westerly winds, a cooler continent, and a warmer peninsula. It did not predict similar but less dramatic trends in winter, which scientists suspect are caused by increases in greenhouse gases.
“It's surprising that the model looks so much like the observations,” says meteorologist Mark Baldwin of Northwest Research Associates in Bellevue, Washington. Baldwin says the researchers make a strong case that what goes on in the stratosphere affects the troposphere. In the future, he adds, ozone effects should diminish as the ozone layer recovers; then greenhouse gases will likely become more prominent actors. Meanwhile, researchers say the next step is to figure out how the stratosphere acts on the troposphere.