Key Concepts

• The land-based ice sheets of Greenland and Antarctica hold enough water to raise global sea level by more than 200 feet.
• A complex “plumbing system” of rivers, lakes and meltwater lies under the ice sheets. That water “greases” the flow of vast streams of ice toward the ocean.
• For millennia, the out­going discharge of ice has been balanced by incoming snowfall. But when warming air or surface meltwater further greases the flow or removes its natural impediments, huge quantities of ice lurch seaward.
• Models of potential sea-level rise from climate change have ignored the effects of subglacial water and the vast streams of ice on the flow of ice entering the sea.

As our P-3 flying research laboratory ­skim­med above the icy surface of the Wed­dell Sea, I was glued to the floor. Lying flat on my stomach, I peered through the hatch on the bottom of the plane as seals, penguins and icebergs zoomed in and out of view. From 500 feet up everything appeared in miniature except the giant ice shelves—seemingly endless expanses of ice, as thick as the length of several football fields, that float in the Southern Ocean, fringing the ice sheets that virtually cover the Antarctic landmass. In the mid-1980s all our flights were survey flights: we had 12 hours in the air once we left our base in southern Chile, so we had plenty of time to chat with the pilots about making a forced landing on the ice shelves. It was no idle chatter. More than once we had lost one of our four engines, and in 1987 a giant crack became persistently visible along the edge of the Larsen B ice shelf, off the Antarctic Peninsula—making it abundantly clear that an emergency landing would be no gentle touchdown.

The crack also made us wonder: Could the ocean underlying these massive pieces of ice be warming enough to make them break up, even though they had been stable for more than 10,000 years?

   
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