Ozone hole blamed for increased rainfall in Australia

Up to 35 per cent more: Study; International climate talks must address impact, researcher says

By MARGARET MUNRO, Postmedia News April 25, 2011 4:04 AM

A Canada-U.S. study, described as a "game changer" for climate science, says Australia can blame its increased rainfall on the Antarctic ozone hole.
The hole has had a profound impact on the Southern Hemisphere, altering the climate all the way to the equator, changing wind patterns and increasing rain in southern Australia by about 35 per cent, according to a study published Thursday in the journal Science.
"It's somewhat like a domino effect, one change leads to another," said Michael Sigmond, a climate scientist at the University of Toronto. He co-wrote the report with researchers at Environment Canada and Columbia University in New York.
The study's impact could - and should - be felt at international climate talks, say the researchers.
"This could be a real game changer," co-author Lorenzo Polvani, from Columbia's Lamont-Doherty Earth Observatory, said in a news release.
He said international agreements about mitigating climate change should not be confined to carbon alone, adding that ozone deserves more attention from the United Nations Intergovernmental Panel on Climate Change.
"The ozone hole is not even mentioned in the summary for policy-makers issued with the last IPCC report," Polvani said. "We show in this study that it has large and farreaching impacts. The ozone hole is a big player in the climate system."
Sigmond agreed the ozone hole deserves more IPCC attention. "After all, the Antarctic ozone hole is found to be the dominant driver of observed changes in the summertime weather patterns in the Southern Hemisphere, from the Pole all the way to the tropics," he said.
The ozone layer is several kilometres above Earth's surface and absorbs harmful ultraviolet rays from the sun that can trigger cancer and damage plants. The Antarctic ozone hole was caused by widespread use of chemicals containing chlorofluorocarbons during the second half of the 20th century. CFC chemicals have been phased out, and the hole is expected to close over the next 50 years as CFCs disappear from the atmosphere.
The researchers used two climate models to assess the hole's impact - one on Environment Canada's supercomputer and the other at the U.S. National Center For Atmospheric Research.
"The beauty of these models is you can change one component of the atmosphere and see what happens," Sigmond said.
Both models show the same impacts of the ozone hole, and the results fit with climate changes that have been seen in the Southern Hemisphere since the hole formed almost three decades ago. All of which "strongly implicates" ozone depletion as a cause of the increased summer precipitation in the subtropics, the scientists said.
Co-author John Fyfe at Environment Canada says the ozone hole has altered the way the atmosphere is heated over Antarctica, triggering a shift in a band of winds known as the westerly jet, which is "analogous to the 'jet stream' people are familiar with in the Northern Hemisphere."
The change in the westerly jet altered moisture transport in the Southern Hemisphere, having the most pronounced impact on Southern Australia with "about a 35-percent increase in rainfall attributable to polar ozone depletion," Fyfe said.
Sigmond said the 35-percent increase over the past 30 years corresponds to up to 30 millimetres more rain per month.

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