Ancient coral heads, white and dead, record an earlier time when the climate warmed and the seas rose. Found just inland in the Florida Keys, Bermuda, and the Bahamas, they date from roughly 130,000 years ago, before the last ice age. These corals grew just below the sea surface, and are now marooned well above it. When they flourished, sea level must have been 15 to 20 feet (five to six meters) higher—which means that much of the water now in Greenland’s ice was sloshing in the oceans.
All it took to release that water was a few degrees of warming. Climate back then had a different driver: not fossil-fuel emissions but changes in Earth’s tilt in space and its path around the sun, which warmed summers in the far North by three to five degrees Celsius (5° to 9°F) compared with today. At the rate the Arctic is now warming, those temperatures could be back soon—“by mid-century, no problem,” says Jonathan Overpeck of the University of Arizona, who has studied the ancient climate. “There’s just unbelievable warming in the Arctic. It’s going much faster than anyone thought it could or would.”
Computer models that forecast how ice sheets will react to the warming tend to predict a sluggish response—a few thousand years for them to melt, shrink, and catch up to the reality of a warmer world. If the models are right, rising seas are a distant threat.
Yet what is happening on the Greenland ice sheet is anything but leisurely. For the past 15 years, Konrad Steffen of the University of Colorado at Boulder has spent each spring monitoring the ice from a camp deep in the interior. Back again in the coastal village of Ilulissat last summer, the Swiss-born climate researcher, lean and weathered from wind and glacial glare, sits with colleagues in a waterfront hotel, waiting out fog that has grounded their helicopter. “Things are changing,” he says. “We see it all over.”
Offshore, flotillas of icebergs drift silvery in the half-light—tangible evidence of the change. Their voyage began nearby in a deep fjord, where a glacier called Jakobshavn Isbræ flows to the sea.
Ice seems rock hard when you crunch an ice cube or slip on a frozen puddle. But when piled in a great mass, ice oozes like slow, cold taffy. On Greenland, it flows outward from the heart of the ice sheet, a dome of ice the size of the Gulf of Mexico, and either peters out on land or follows fast-flowing ice streams all the way to the ocean. Four miles (six kilometers) wide and several thousand feet thick, Jakobshavn is an icy Amazon, disgorging more ice than any other Greenland glacier.