{"id":11663,"date":"2011-03-09T15:08:34","date_gmt":"2011-03-09T23:08:34","guid":{"rendered":"http:\/\/blogs.kqed.org\/climatewatch\/?p=11663"},"modified":"2011-03-09T15:08:34","modified_gmt":"2011-03-09T23:08:34","slug":"melting-ice-sheets-spur-sea-level-rise","status":"publish","type":"post","link":"https:\/\/ww2.kqed.org\/climatewatch\/2011\/03\/09\/melting-ice-sheets-spur-sea-level-rise\/","title":{"rendered":"Melting Ice Sheets Spur Sea Level Rise"},"content":{"rendered":"

By Michael D. Lemonick<\/a><\/p>\n

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\nA new study says melting ice sheets will likely be “the dominant contributor to sea level rise in the 21st century.\u201d<\/strong><\/p>\n

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A tidewater glacier in Greenland, pictured in 2008. (Photo: Michael Lemonick)<\/figcaption><\/figure>\n<\/div>\n

About 110,000 years ago, global sea level began to drop as the planet cooled, and evaporating seawater was transformed into massive ice sheets that covered large parts of the Northern Hemisphere. About 10,000 years ago, the Earth warmed up again. The ice retreated dramatically, and sea level rose. Since then, the planet\u2019s ice, and the level of the ocean have been more or less stable.
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\nNot any more, though. Thanks largely to human-generated greenhouse gases, the ice that remains in mountain glaciers and ice caps \u2014 and more significantly, in the massive ice sheets that smother Antarctica and Greenland under frigid blankets up to two miles thick in places \u2014 is moving to the sea once again. Just how high and how fast global sea level will rise as a result is still uncertain, though. One big reason: scientists haven\u2019t been able to get a firm handle on how ice melting has already changed as a consequence of the warming that\u2019s already taken place.<\/p>\n

A new paper<\/a> in the journal Geophysical Research Letters<\/em> is sure to help, though. Using two different measurement techniques, a team of geophysicists from the U.S. and Netherlands has shown that the ice in Antarctica and Greenland is not only vanishing into the sea: the rate of disappearance has been accelerating over an 18-year period, with about 36.3 billion metric tons more ice lost each year compared to the year before.<\/p>\n

By 2006, a year in which a total of about 475 billion metric tons of ice were lost, the acceleration in ice mass loss from the ice sheets had already surpassed acceleration in ice mass loss from mountain glaciers and ice caps \u2014 and that lead is likely to grow over the coming century, the study indicates, to the point where ice sheets will be “the dominant contributor to sea level rise in the 21st<\/sup> century.\u201d<\/p>\n

What makes this study so important, says co-author Isabella Velicogna, of the University of California, Irvine and NASA\u2019s Jet Propulsion Laboratory<\/a> in Pasadena, is that the ice loss was measured in two entirely independent ways. The first involved the Gravity Recovery and Climate Experiment, or GRACE<\/a>. It\u2019s a pair of satellites that measure the local gravity at every spot on Earth. In both Greenland and Antarctica, the ice generates some of that gravity \u2014 and as the ice melts in response to warming air and ocean temperatures, the gravity diminishes. \u201cGRACE basically weighs the ice every 30 days,\u201d says Velicogna, \u201cand sees how much it\u2019s changing.\u201d<\/p>\n

How Do We Know: Greenland\u2019s Melting Ice Sheet<\/a> from Climate Central<\/a> on Vimeo<\/a>.<\/p>\n