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 Antarctic ozone hole is about one-third to blame for Australia's recent series of droughts, say scientists.
Writing in the journal Science, they conclude that the hole has shifted wind and rainfall patterns right across the Southern Hemisphere, even the tropics.
Their climate models suggest the effect has been notably strong over Australia.
Many parts of the country have seen drought in recent years, with cities forced to invest in technologies such as desalination, and farms closing.
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.
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 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.
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.
“The ozone hole results in a southward shift of the high-latitude circulation — and the whole tropical circulation shifts southwards too,” explained Columbia's Sarah Kang.
Much of the cold weather felt in the U.K. over the last couple of winters, for example, was caused by blocking of the Northern Hemisphere stream. The Columbia team found that overall, the ozone hole has resulted in rainfall moving south along with the winds.
But there are regional differences, particularly concerning Australia.
“In terms of the average for that zone, .125the ozone hole drives.375 about a 10 per cent change — but for Australia, it's about 35 per cent,” Dr. Kang told BBC News.
Their modelling indicated that global warming due to greenhouse gas emissions was also a factor — though natural climate cycles are also thought to be important, as Australia suffered severe droughts in the era before ozone depletion and before the warming seen in the late 20th Century.
“This study does illustrate the important point that different mechanisms of global change are contributing to the climate impacts we're seeing around the world,” observed Professor Myles Allen of Oxford University, a leading U.K. climate modeller.
“It's very important to unpack them all rather than assuming that any impact we see is down simply to greenhouse gas-mediated warming.”
Ozone depletion is caused by chemical reactions in the stratosphere, the upper atmosphere.
Ultraviolet rays
The ozone layer blocks the Sun's harmful ultraviolet rays, which can cause skin cancer and other medical conditions.
Earlier this month, the World Meteorological Organisation revealed that the Arctic was experiencing the worst ozone depletion on record — a consequence of unusual weather conditions.
But the forecast is that even the Antarctic ozone hole — which is more severe than its Arctic equivalent — should be repaired by 2045-60.
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