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 metres (23 feet), flooding New York and London, and drowning 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 (50 miles) 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 (624,000 cubic miles) 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 U.S. government advisory committee on abrupt climate change.
In the past 15 years, winter temperatures have risen about 5 degrees Celsius (9 Fahrenheit) on the cap, while spring and autumn temperatures increased about 3 degrees Celsius (5 Fahrenheit). Summer temperatures are unchanged.
Swiss-born Steffen is one of dozens of scientists who have peppered the Greenland ice cap with instruments to measure temperature, snowfall and the movement, thickness and melting of the ice.
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 Celsius (minus 22 Fahrenheit) to scrutinise 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 (9 miles) 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."
FISH AND TOURISTS
Two to three days' worth of icebergs from this glacier alone produce enough fresh water to supply New York City for a year.
The rush of new water leaves scientists with crucial questions about how much sea levels could rise and whether the system of ocean currents that ensures Western Europe's mild winters -- known as the "conveyor belt" -- could shut down.
"Some models can predict a change in the conveyor belt within 50 to 100 years," said Steffen. "But it's one out of 10 models. The uncertainty is quite large."
If you're a fisherman in Greenland, however, global warming is doing wonders for your business.
Warmer waters entice seawolf and cod to swim farther north in the Atlantic into Greenlandic nets. In this Disko Bay town, the world's iceberg capital, the harbour is now open year-round because winter is no longer cold enough to freeze it solid.
Warmer weather also boosts tourism, a source of big development hopes for the 56,000 mostly Inuit inhabitants of Greenland, which is a self-governing territory of Denmark.
Hoping to lure American visitors, Air Greenland launched a direct flight from Baltimore last month, and there is even talk of "global warming tourism" to see Warming Island.
One commentator, noting the carbon dioxide emissions such travel would create, has called that "eco-suicide tourism".
(To read more, including excerpts from the Reuters interview with Konrad Steffen, director of University of Colorado at Boulder's Cooperative Institute for Research in Environmental Sciences, go to the Reuters Environment blog at http://blogs.reuters.com/category/from-reuterscom/environment)