Antarctica's ice sheet melting naturally

Searching for rocks in West Antarctica's mountains

The West Antarctic Ice Sheet (WAIS) has been melting naturally and releasing water to the ocean for the last 10,000 years.

Research published in the journal Science suggests that the last Ice Age never really ended in that part of the world.

If the melting continues at its current rate then the WAIS could disappear in 7,000 years, possibly raising worldwide sea levels by five metres.

However, scientists warn that a sudden rapid melting of the WAIS could cause serious problems for some coastal regions.

Rock climbing

Geologists measured the chemical composition of rocks collected on seven mountains in the Ford Ranges near the Ross Sea.

Some of the peaks are almost a mile high (1.6 kilometres), but were completely covered in ice 10,000 years ago.

As the ice began to melt away and the glaciers retreated, rocks where left behind on the freshly uncovered mountains.

The rocks were exposed to cosmic rays from deep space and so their chemical make-up changed.

By looking at the composition of the rocks, the geologists could calculate how old they were and therefore when the ice melted.

Ice Age

Professor John Stone from the University of Washington, US, led the teams behind the work.

He said: "In all cases we got very tight, consistent correlations of age with altitude, so we are able to track the margins of the ice sheet coming down the mountain sides with this approach."

Antarctica's Ice Age may not be over

The most surprising finding though is how recently the ice has thinned in West Antarctica.

Ice sheets in North America and Europe had nearly all melted 10,000 years ago, but this process had only just started in West Antarctica at that time.

"The Ice Age never really came to an end in that part of the world," Professor Stone said.

The WAIS, which covers an area of 360,000 square miles (580,000 km), is currently melting at a slow and steady rate and if this continues it will disappear in another 7,000 years.

Professor Stone says this would raise the global sea levels by about five metres.

But he warns: "A rapid melting event that released even a small fraction of this amount could have disastrous consequences for coastal regions."

The scientists stress this melting of the WAIS is a natural process but they cannot rule out that global warming may now be playing a part.

As much of the ice sheet is below water, the WAIS could be very sensitive to the warming of the oceans.