Wednesday, April 22, 2009

Antarctic sea ice increasing: study

By Simon Santow for AM

ABC News Online

23 April 2009

In recent years all the headlines have been about ice melting in some of the globe's chilliest places. But it seems that global warming may actually be leading to an increase in sea ice in parts of the Antarctic.

Scientists in the United Kingdom have produced a study which shows ice has grown by 100,000 square kilometres each decade in the past 30 years.

And perversely the increase is being put down to the hole in the ozone layer.

Scientists such as Julienne Stroeve from the National Snow and Ice Data Centre in the United States say they are not that surprised by the news of the study and its findings.

"There's been a change in atmospheric circulation around Antarctica related to the stratospheric ozone depletion and this actually causes stronger winds, which then pushes the ice away from the coast in some regions of Antarctica, which actually then causes more new ice formation and increases the overall sea ice in that region," she said.

The British Antarctic Survey combined with NASA to look at the levels of ice in the region over the long term.

What was clear was that climate change produces complex results. Instead of a widening hole in the ozone layer, produced by human activity, warming temperatures as they have in the Arctic, in Antarctica it was having the opposite effect.

"In other parts of Antarctica the temperatures have been decreasing and this is again sort of what we've expected to see, at least according to what the climate models tell us should be happening," Dr Stroeve added.

"But if you look at the Antarctic Peninsula for example, that's where you've had really strong warming and you've had a warming of about 3 degrees Celsius in the last 50 years.

"And if you look at changes in sea ice in that region they all show very strong negative trends.

"The paper shows an overall positive trend if you look at all of Antarctica, but there's regional differences that are quite different from different regions.

"We have to deal with what we know about warming in certain regions and changes in circulation and wind patterns in other regions."

Dr Stroeve argues that the rate of ice expansion, even as it translates to hundreds of thousands of square kilometres, is relatively insignificant.

"This recent paper shows you know a change in the annual mean ice extent of Antarctica of only 0.97 per cent per decade which is really close to zero," she added.

"In contrast if you look at the Arctic, you see statistically significantly trends of about 4 per cent per decade in the opposite direction right now if you look at the annual mean. Certainly it's a very small change for the Antarctic.

"The Antarctic is very different than the Arctic and what we're noticing is that you'll see negative trends in some areas of the Antarctic and positive trends elsewhere."

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