National Geographic News
Two depictions of the ozone hole, one in 1979 and one in 2008; the newer image shows a marked degradation.

Image courtesy NASA Earth Observatory

By Kate Ravilious

National Geographic News

January 27, 2010

While most of the world has warmed, parts of the southern hemisphere have remained stubbornly cold—oddly enough because of a gaping hole in the ozone layer. Now new research shows that all the efforts made by scientists and environmental advocates to close the hole may actually increase warming throughout the entire southern hemisphere.

That's because, for decades, brighter summertime clouds, created by the hole, have reflected more of the sun's rays, acting as a shield against global warming.

As the ozone layer heals and the clouds dissipate, this “will lead to a rise in temperature [in parts of the southern hemisphere] faster than currently predicted by models," said study leader Ken Carslaw of the U.K.'s University of Leeds.

(Related: "Antarctica Heating Up, 'Ignored' Satellite Data Show.")

Mixed Success

In 1985 scientists from the British Antarctic Survey discovered a giant hole in the ozone layer in the upper atmosphere over Antarctica. Ozone in the upper atmosphere absorbs harmful ultraviolet rays from the sun.

The subsequent global agreement to ban chlorofluorocarbons (CFCs)—the chemicals largely responsible for the thinning of the ozone layer—reversed the growth of the ozone hole and was deemed one of the biggest environmental success stories of the 20th century.

(Related: "Laughing Gas Biggest Threat to Ozone Layer, Study Says.")

But the healing process is slow: Since the early 1980s changes in the upper atmosphere caused by ozone depletion have intensified circumpolar winds that whistle around Antarctica.

Using a computer model and two decades worth of meteorological data, Carslaw and colleagues discovered that the fiercer winds whip up more sea spray. This throws more salt particles into the air and encourages the formation of brighter clouds, which reflect sunlight back into space and have a cooling effect.

The summertime cooling caused by the ozone hole since 1980 has approximately cancelled out the warming caused by rising carbon dioxide emissions, Carslaw said.

Findings published online January 27 in the journal Geophysical Research Letters.



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