NewsJuly 18, 2012

Greenland Glacier Sheds Two Manhattans' Worth of Ice

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Michael D. Lemonick

By Michael D. Lemonick

Greenland’s massive ice sheet drains slowly to the sea, but until the last decade or two, the drainage was balanced by new snow that fell every winter. Not anymore, though: thanks to rising global temperatures. Greenland has begun shedding ice at a prodigious rate, a major factor in the sea level rise that poses a greater threat to life and property with every passing year. 

Usually, glacial ice enters the sea in chunks the size of buildings, but satellite images are showing the Petermann Glacier, in northwest Greenland, has let go of a slab of ice twice the size of Manhattan. It isn’t the first time the Petermann has lost so much ice at once: back in 2010, an even bigger piece — as big as four Manhattans put together — broke free. And last year, glaciologist Jason Box of the Byrd Polar Research Center at Ohio State University’s told the New York Times that another big piece was set to go.

The Petermann Glacier. Credit: NASA.

Now it has: the vast new ice island is floating toward the Nares Strait, a body of water that separates the Arctic Ocean from Baffin Bay. Unlike some icebergs, this one won’t add to sea level rise itself because the end of the Petermann Glacier is already floating. The breakup is probably caused by rising air and ocean temperatures, which had until recently spared the northernmost parts of Greenland.

As the Petermann Glacier and other tidewater glaciers (that is, glaciers that reach the sea) lose ice at their seaward ends, the uphill parts can slide more easily — so even if the new ice island doesn’t add to rising seas, it could eventually make the Petermann a significant contributor, as glaciers in the south of Greenland already are.

That also goes for glaciers much further to the south — glaciers at the other end of the world, in Antarctica. Recent studies have shown that warmer ocean temperatures could soon be causing significant ice loss from the ice sheets that blanket the South Pole. The last time it was as warm as it is now, about 120,000 years ago, sea level was up to 29 feet higher than it is today. And for it to have gone that high, Antarctic melting must have been part of the mix.

No one knows for sure what that means for our own future. But if the air and water keep warming, and ice keeps plopping into the sea, it can’t be good.