Ozone hole ‘changing weather’

The Antarctic ozone hole is changing weather patterns across the Southern Hemisphere, even affecting the tropics, scientists have concluded.

The scientists behind the new study added the ozone hole into standard climate models to investigate how it might have affected winds and rains.

Writing in the journal Science, they say rainfall has moved further south, towards the pole.

They deduce that the effect has been notably strong over Australia.

“The ozone hole results in a southward shift of the high-latitude circulation – and the whole tropical circulation shifts southwards too,” explained study leader Sarah Kang from Columbia University in New York.

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 UK over the last couple of winters, for example, was caused by blocking of the Northern Hemisphere stream.

Going south

The 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, [the ozone hole drives] about a 10% change – but for Australia, it’s about 35%,” Dr Kang told BBC News.

Their modelling indicated that global warming due to greenhouse gas emissions is also a factor in changing precipitation patterns.

Natural climate cycles are also thought to be important, as different rainfall patterns were noted in the era before ozone depletion and late 20th Century warming.

“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 UK 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.

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

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 Organization 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.

23 April: This article has been changed to correct misinterpretations of the Science paper that were contained in the original.

Source: bbc.co.uk