Ozone Hole’s Closing Could Affect Climate

June 10 2008 A new study led by Seok-woo Son and Lorenzo Polvani, in the Department of Applied Physics and Applied Mathematics at SEAS, is suggesting that the winds in the Southern Hemisphere will be greatly impacted by the expected recovery of the ozone hole in the second half of this century. In a study that appears in the June 13 issue of Science, Seok-Woo Son, lead-author and a postdoctoral research scientist at SEAS, and Professor Polvani suggest that stratospheric ozone ought to be more carefully considered by the next Intergovernmental Panel on Climate Change (IPCC) round of climate model predictions.

"We were surprised to find that the closing of the ozone hole, which is expected to occur in the next 50 years or so, shows significant effects on the global climate," said Lorenzo M. Polvan one of two principle investigators and professor of applied mathematics at SEAS. "This is because stratospheric ozone has not been considered a major player in the climate system. We believe the closing of the ozone hole is likely to have profound impacts on the surface winds and, also likely, to have an impact on other aspects of the Earth's climate, including surface temperatures, locations of storm tracks, extent of dry zones, amount of sea ice, and ocean circulation."

In the past few decades, the tropospheric winds in the Southern Hemisphere have been accelerating closer to the planet's pole as a result of increasing greenhouse gases and decreasing ozone, says Polvani. This wind change has had a broad range of effects on the Earth's climate and the IPCC models predict that this effect will continue, albeit at a slower pace. In contrast, Polvani says, predictions made by the chemistry-climate models of the Scientific Assessment of Ozone Depletion, published by the World Meteorological Organization in 2006, indicate that, as a consequence of ozone recovery--a factor largely ignored by IPCC models--the tropospheric winds in the Southern Hemisphere may actually decelerate in the high latitudes and move toward the equator, potentially reversing the direction of climate change in that hemisphere.

The Earth's ozone layer, which lies just above the troposphere, catches harmful ultraviolet rays from the sun and was, until the Montreal Protocol, being eroded by pollution caused by the widespread use of aerosols powered by chlorofluorocarbons (CFCs). Recent observations indicate that the ozone layer is no longer in danger and is expected to recover. As a consequence, the new study finds, the Southern Hemisphere climate change may also reverse.

"Our results suggest that stratospheric ozone is important for the Southern Hemisphere climate change, and ought to be more carefully considered in the next set of IPCC model integrations," says lead-author Seok-Woo Son.

In addition to the two SEAS researchers, eight other scientists--from Johns Hopkins; the National Institute for Environmental Studies in Tsukuba, Japan; the National Center for Atmospheric Research in Boulder, CO; the NASA Goddard Space Flight Center in Greenbelt, MD; the Institute for Atmospheric and Climate Sciences at ETH in Zurich, Switzerland; the Physical Meteorological Observatory in Davos, Switzerland; the University of Toronto; and the Meteorological Research Institute in Tsukuba, Japan­--participated in the study.