Protecting vital infrastructure as sea levels rise

front is 25 kilometers across and 500 meters thick, and moves at over 10 meters per day. The seabed there is 1000 meters down and is made of sediment hundreds of meters thick and the consistency of toothpaste.” Not an ideal building site.

A slightly more subtle scheme to rein in the glaciers was proposed more than twenty years ago by Douglas MacAyeal of the University of Chicago. His idea is to fight ice with ice. The big outlet glaciers feed into giant floating shelves of ice, which break off into icebergs at their outer edges. MacAyeal suggested pumping water up from beneath the ice and depositing it on the upper surface, where it would freeze to form a thick ridge, weighing down the floating ice shelf. Add enough ice in this way, and the bottom of the ice shelf would eventually be forced down onto the seabed. Friction with the seabed would slow down the shelf’s movement, which in turn would hold back the glaciers feeding into it. It would be like tightening a colossal valve.

“I think it’s quite an inspired idea,” says Bindshadler. Nobody, however, has followed it up to work out how practical the scheme would be. “On the back of an envelope it has promise — but these ice shelves are big. You would need a lot of drilling rigs all over the ice shelf, and my intuition is that if you look at the energetics of it, it won’t work,” Bindshadler says.Reversing sea level riseEven if we could apply brakes to glaciers, this would only slow down sea level rise. Could we do better than that and reverse it — actually make the sea retreat? If you think of the sea as a giant bathtub, then the most obvious way to lower its level is to take out the plug.

“One of the oldest notions is filling depressions on the land,” says MacCracken. Among the largest of these is the Qattara depression in northern Egypt, which at its lowest point is more than 130 meters below sea level. Various schemes have been proposed to channel water from the Mediterranean into the depression to generate hydroelectric power, and as a by-product a few thousand cubic kilometers of the sea would be drained away.

Unfortunately, this is only enough to shave about 3 millimeters off sea level: a drop in the ocean. There would also be