Atop Greenland's Suicide Cliff, from where old Inuit women used to hurl themselves when they felt they had become a burden to their community, a crack and a thud like thunder pierce the air.

"We don't have thunder here. But I know it from movies," says Ilulissat nurse Vilhelmina Nathanielsen, who hiked with us through the melting snow. "It's the ice cracking inside the icebergs. If we're lucky we might see one break apart."

It's too early in the year to see icebergs crumple regularly but the sound is a reminder. As politicians squabble over how to act on climate change, Greenland's ice cap is melting, and faster than scientists had thought possible.

A new island in East Greenland is a clear sign of how the place is changing. It was dubbed Warming Island by American explorer Dennis Schmitt when he discovered in 2005 that it had emerged from under the retreating ice.

If the ice cap melted entirely, oceans would rise by 7 meters, flooding New York and London, and drowning whole island nations like the Maldives.

A total meltdown would take centuries but global warming, which climate experts blame mainly on human use of fossil fuels, is heating the Arctic faster than anywhere else on Earth.

"When I was a child, I remember hunters dog-sledding 80 km on ice across the bay to Disko Island in the winter," said Judithe Therkildsen, a retiree from Aasiaat, a town south of Ilulissat on Disko Bay.

"That hasn't happened in a long time."

Losing more ice than the Alps

Greenland, the world's largest island, is mostly covered by an ice cap of about 2.6 million cubic km that accounts for a 10th of all the fresh water in the world.

Over the last 30 years, its melt zone has expanded by 30 percent, and now the cap loses 100 to 150 cubic km of ice every year - more than all the ice in the Alps.

"Some people are scared to discover the process is running faster than the models," said Konrad Steffen, a glaciologist at University of Colorado at Boulder and a Greenland expert who serves on a US government advisory committee on abrupt climate change.

In the past 15 years, winter temperatures have risen about 5 C on the cap, while spring and autumn temperatures increased about 3 C.

Since 1990, Steffen has spent two months a year at Swiss Camp, a wind-swept outpost of tents on the ice cap, where he and other researchers brave temperatures of minus 30 C to scrutinize Greenland's climate change clues.

The more the surface melts, the faster the ice sheet moves towards the ocean. The glacier Swiss Camp rests on has doubled its speed to about 15 km a year in the last 12 years, just as its tongue retreated 10 km into the fjord.

"It is scary," said Steffen. "This is only Greenland. But Antarctica and glaciers around the world are responding as well."

Source:China Daily/Agencies