The recovery of the ozone layer is considered essential for the health of the planet's living creatures, but new research suggests it could also assist in the fight against global warming. In the 13 June issue of Science, climatologists report that ozone recovery could restore wind patterns in the Southern Hemisphere that have blown out of kilter due to ozone depletion and the buildup of greenhouse gases.
Ever since 191 nations signed the 1987 Montreal Protocol, which banned the manufacture of ozone-destroying chemicals called chlorofluorocarbons, the fragile ozone layer has been set on a slow path to recovery. The layer's return to full health will likely take another 60 years. By then, the so-called ozone hole should no longer appear over Antarctica every polar spring and persist until autumn. And the cancer-causing ultraviolet (UV) rays that ozone filters out of sunlight will largely be blocked from hitting the surface.
Ozone has another, less obvious effect, on global climate. Over the past 50 years, the Antarctic ozone hole has amplified a key cyclonic wind pattern in the Southern Hemisphere called the Southern Annular Mode (SAM). A dense ozone layer heats the underlying stratosphere, 12 to 50 kilometers above Earth's surface, while the ozone hole leads to cooling. Affected by both the greenhouse-gas buildup at lower altitudes and the cooler stratosphere, SAM has blocked warmer air from reaching Antarctica, resulting in an icier continent but warming just about everywhere else south of the equator.
As the ozone hole recovers and SAM returns to more normal patterns, researchers predict that these effects will start to decrease over the Southern Hemisphere. In the new study, an international team compared standard climate change computer models with other versions that take stratospheric chemistry into account. The comparison showed that ozone recovery should restore SAM's traditional pattern of winds. "It's a welcome effect," says climate scientist and co-author Lorenzo Polvani of Columbia University. "Our study shows that ozone recovery might ease the effects of climate change" in the Southern Hemisphere.
How might a dwindling SAM impact Antarctica? "We can't draw conclusions right now," says atmospheric scientist Judith Perlwitz of the University of Colorado, Boulder. "We just have questions." And that uncertainty, she adds, highlights the need to continue monitoring the effects of ozone on climate change.
[Editor's note: This story replaces an earlier version.]