Ozone hole has dried Australia, says study

Richard Black

  

AFP Former Marshal Rodda (left) and farmhand Gilbert Fryatt inspect an empty dam, leaving them with fields of stunted wheat stalks, normally thigh high, and which have managed only a few inches growth in the parched earth of the Australian wheat belt area of Wimmera, northwest of Melbourne. File photo

 

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 scientists behind the new study — led from Columbia University in New York — added the ozone hole into standard climate models to investigate how it might have affected winds and rains.

“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.

Of particular interest was the southward migration of the Southern Hemisphere jet stream. These high-altitude winds are key to determining weather patterns, in both hemispheres.

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.

The chemicals involved derive from substances such as chlorofluorocarbons (CFCs) and their relatives, which used to be staples in air-conditioning, refrigeration and aerosol cans.

Though the U.N. Montreal Protocol has significantly curbed emissions of these substances, they endure for decades in the atmosphere, and so their effects are still being felt.

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.

Dr. Kang cautions that this alone will not restore prior climate conditions to Australia or anywhere else in the Southern Hemisphere. — © BBC News/Distributed by the New York Times Syndicate