22 January 2009

Global warming hitting Antarctica hard

Agence France-Presse
Scientists have unveiled evidence to suggest global warming is affecting all of Antarctica, home to the world's mightiest store of ice.
West Antarctic warming

Southern heat: This illustration depicts the warming that scientists have determined has occurred in West Antarctica during the last 50 years, with dark red showing the area that has warmed the most. Credit: NASA; Credit E. J. Steig.

PARIS: Scientists have unveiled evidence to suggest global warming is affecting all of Antarctica, home to the world’s mightiest store of ice.

The average temperature across the great southern continent has been rising for the last half century and the finger of blame points at the greenhouse effect, they said.

The research, published today in the British journal Nature, takes a fresh look at one of the great unknowns ¬– and dreads – in climate science.

Coastal risk

Any significant thaw of Antarctica could drown many coastal cities and delta regions. Bigger than Australia, Antarctica holds enough ice to raise global sea levels by 57 metres.

Previous monitoring has already pinpointed the Antarctic Peninsula – the tongue that juts 800 kilometres towards South America – as a “hotspot” where hundreds of glaciers have been in retreat since the start of the decade.

But until now the news has been reassuring regarding Antarctica’s two massive icesheets.

Indeed, a common belief is that the icy slabs have even cooled slightly and possibly thickened, partly in response to the chilling seasonal effects of the ozone hole over the South Pole.

Mistaken belief

Not so, the new study says. It calculates that West Antarctica has been warming by 0.17 ºC per decade over the past 50 years. This is even more than the Peninsula, where the average rise is estimated as 0.11 ºC per decade.

There has indeed been some cooling in East Antarctica, but this was mainly in the autumn, and occurred as a result of the ozone hole. There was also a period of strong cooling between 1970 and 2000.

But, overall and when calculated over 50 years, East Antarctica has warmed too – by an average of 0.1 ºC per decade, a figure that the authors describe as “significant”.

“The sense of ‘oh, it’s cooling in East Antarctica,’ is based essentially on the 1970 to 2000 period, and it’s warmed since then – although we don’t have a lot of data for the most recent period – and it definitely warmed prior to the 1970s,” said Eric Steig, a professor of Earth and space sciences at the University of Washington.

“When you look at the big picture on that, the average [trend in East Antarctica] is actually warming,” he said.

Put together, the average temperature rise for Antarctica is put at 0.12 ºC per decade, the study said.

The work is based on a 25-year archive of observations by satellites measuring the intensity of infrared light radiated by the snow pack. These were buttressed by data from automated weather stations deployed around the Antarctic coast since 1957.

Careless statements

The paper does not venture any estimate about ice loss or predict the icesheets’ stability, but says only global warming can logically explain the temperature trend.

“This shouldn’t cause anyone to worry more than they did before. But what it does do is kill off the rather silly and careless statements out there from some people to the effect that Antarctica’s cooling,” said Steig.

Such comments “put into question all the other science that supports the idea that there is warming and it’s human beings’ fault,” he said.

There could be bad news a few decades down the road, when efforts to fix the ozone hole bear fruit, added Steig.

Ozone hole

“The hole could be eliminated by the middle of this century. If that happens, all of Antarctica could begin warming on a par with the rest of the world,” he warned.

The West Antarctic icesheet, which holds enough ice to boost global sea levels by up to six metres, lies at an average height of about 1,800 metres.

The East Antarctic icesheet, divided from West Antarctica by a mountain chain, has an average elevation of around 3,000 m, which makes it not only bigger but also colder.

If it melted in its entirety – something that most scientists discount except only as a very distant doomsday scenario – today’s coastlines would be drowned to a height of 50 m.

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