Now climate-change scientists say ozone hole stops global warming

Published on Monday 25 January 2010 21:47

IT WAS once regarded as one of the biggest environmental threats to the planet.

Now there is mounting evidence that the ozone hole above the Antarctic has been protecting the southern hemisphere against global warming.

The bizarre side-effect of ozone depletion has been studied by scientists at the University of Leeds.

The ozone hole, caused by chlorofluorocarbons (CFCs) released into the atmosphere, is now steadily closing, but the research has suggested this could actually increase warming.

Scientists discovered brighter summertime clouds had formed over the area below the hole, which reflect more of the sun's powerful rays.

"These clouds have acted like a mirror to the sun's rays, reflecting the sun's heat away from the surface to the extent that warming from rising carbon emissions has effectively been cancelled out in this region during the summertime," said Professor Ken Carslaw, who co-authored the research.

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When the ozone hole seals, he expects an acceleration in warming in that region, he added.

During the 1980s, there were widespread warnings that UV exposure caused by the depleting ozone layer would have devastating impacts ranging from a rise in skin cancer, to damage to plants, to reduction of plankton.

The Leeds team found that beneath the Antarctic ozone hole, high-speed winds whip up large amounts of sea spray, which contains millions of salt particles.

This spray then forms clouds, and the increased spray over the last two decades has made these clouds brighter and more reflective – helping to keep global warming in check.

Prof Carslaw described the phenomenon as an "unexpected and complex climate feedback".

He highlighted that atmospheric impacts on the climate were "inordinately complicated" and it was not unusual for unexpected consequences to be revealed.

"It's a bit like the El Nino affecting weather in the UK even though it's in the Pacific," he said.

He said the findings of the research did not mean the ozone hole should be kept open.

"You can't correct two wrongs in that way," he said. "The ozone hole was potentially a major catastrophe for the planet that was only stopped by the Montreal Protocol, so we can't go back on that."

Instead, he said it was essential for carbon emissions to be slashed in the same way that CFCs – the ozone-depleting substances in aerosols – were cut under the 1987 Montreal Protocol.

The Leeds team made its prediction using a global model of aerosols and two decades of meteorological data.

The research, which will be published in Geophysical Research Letters online, was funded by the Natural Environment Research Council and the Academy of Finland.