Antarctic ozone hole alters Southern Hemisphere climate

Nacreous clouds or 'mother of pearl' clouds photographed in the sky over Mawson, Antarctica.
These rarely seen 'nacreous' clouds in the stratosphere over Mawson, Antarctica, promote chemical changes in the atmosphere that destroy ozone. The clouds only occur at high polar latitudes in winter at temperatures less than -80 degrees Celcius. (Photo: Renae Baker)
A scientist releases an ozone balloon at Davis

The Antarctic ozone hole has caused significant changes in Southern Hemisphere surface climate in the summer, according to the latest scientific assessment for ozone depletion released today.

The Assessment for Decision Makers, published by the World Meteorological Organisation, reports that ozone depletion in the Antarctic stratosphere (10-50 km above the Earth’s surface) is very likely the dominant cause of a southward shift of summertime weather patterns in the Southern Hemisphere.

Australian Antarctic Division atmospheric scientist, Dr Simon Alexander, who co-authored a chapter of the Assessment, said cooling in the Antarctic lower stratosphere, as a result of ozone depletion, had very likely shifted the region of mid-latitude strong westerly winds and associated rainfall southward.

“Antarctic ozone depletion has also likely contributed to a southward expansion of the tropical circulation in summer and it may have increased subtropical rainfall,” he said.

Dr Alexander said the Antarctic ozone hole would continue to form each spring, and its recovery is not expected until the middle of the century, due to the long lifetime of ozone depleting substances, such as chlorofluorocarbons (CFCs), in the stratosphere.

“We will continue to observe unnaturally high levels of harmful UV radiation over Antarctica for many years to come,” he said.

Australia was amongst the first countries to ratify the Montreal Protocol to phase out ozone depleting substances, after it was opened for signature by the United Nations General Assembly on 16 September 1987.

The 2014 Assessment for Decision-Makers finds that the amount of these ozone depleting substances continues to decrease in the troposphere (0 -10 km above Earth’s surface), as a result of the phasing out of CFC production. It also finds that the abundance of stratospheric chlorine and bromine (which separate from CFC molecules upon exposure to sunlight) has decreased by 10–15% from its peak level observed around year 2000.

The Assessment for Decision-Makers marks the culmination of two years work by 282 scientists from 36 countries. The Assessment will be used by the parties to the United Nations Montreal Protocol to inform policy decisions on the future protection of the ozone layer and control of ozone depleting substances.