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.