Jakobshavn Glacier, Greenland ? If Manhattan floods, it may start here, on an ice field that stretches in frozen silence to every horizon.

Global warming is working away at the Greenland ice cap. The frozen interior of the Arctic island is shedding ice much faster than simple melting should explain. And George Tsoflias wants to know why.

A sharp wind knifes at the hands of the scientist as he struggles – gloves off in the bitter cold – to make adjustments to his radar. His instrument is strapped to an unwieldy wooden sled adorned with batteries and cables and two sets of flat antennas that extend like flapping wings over the snow. He hopes it will peer through the ice to the ground two miles below.

Dozens of scientific teams are scattered over the frigid Greenland snowscape, sent by the National Science Foundation, NASA and universities around the world. They are drilling the ice to collect samples, flying over it with radar and lasers, listening to its creaks and groans with seismometers, fitting it with GPS receivers to measure its pace, and photographing it as it slides to the sea and breaks into icebergs.

Their quest is crucial: If all the ice on Greenland were to melt, the seas around the world would rise by 23 feet, submerging countless coastal cities. A modest 3-foot rise would endanger 70 million people. “Greenland has the potential to put a lot of water, a lot of ice, into the sea,” said Tsoflias, a researcher from Kansas University.

Greenland’s ice cap contains 800 trillion gallons of water and several outlet glaciers, huge rivers of ice that act as faucets from the ice cap. Those faucets are running faster. The Jakobshavn Glacier where Tsoflias works has doubled its speed in five years and every day dumps enough ice into the sea to supply 20 to 30 New York Cities with water.

“It’s the fastest-flowing glacier in the world,” said Don Voigt, huddled in a tent a few yards from Tsoflias’ people. “The question is, why is it flowing so fast?”