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.

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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.