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What Happens When Ice Bridges Start Shattering?

If you're looking for more news on the shattering of that massive ice bridge that was holding Antarctica's Wilkins Ice Shelf in place, Charlie Petit has a great round-up. Or you can watch the video here, which is grimly fascinating.

The Wilkins is roughly the size of Connecticut and is the largest of ten or so shelves to have shrunk or collapsed on the Antarctic Peninsula in recent years. Everyone's fingering climate change as the culprit, as the continent has warmed by about 3C (or 5.4F) in the past half-century. (Here's a good summary of why the poles heat up more rapidly than the rest of the planet.) The good news is that the ice shelves are already submerged in water, so if they do start washing away or melting, it won't directly impact sea levels. The bad news is that when the shelves start shrinking, the glaciers and landed ice behind them start to slide into the ocean more quickly—and that does raise sea levels.

Joe Romm has a post today asking a pressing question: "How much can West Antarctica plausibly contribute to sea level rise by 2100"? His read of recent studies suggests that if we do nothing about emissions, the answer could be as high as three to five feet—and that's just the West Antarctic ice sheet's contribution (melting inland glaciers, Greenland's ice sheet, and the thermal expansion of the oceans will also pitch in). Romm also surveys the debate over how stable the West Antarctic Ice Sheet really is, and comes away with a more mixed, though not terribly consoling, picture. The whole thing probably won't collapse this century, fingers crossed, but enough of the sheet can still plunge into the ocean to cause very large sea-level rises.

Anyway, it's the same story in Antarctica as you see pretty much anywhere else—the changes are happening more quickly than most scientists had expected. (See, for example, this Reuters write-up of two new studies showing faster-than-projected melting at both poles.) Turns out the skeptics were right. The models and forecasts were mistaken. They were just off in the wrong direction...

--Bradford Plumer