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Then there are those gigantic stores of ice in Greenland and Antarctica. During the last interglacial period, sea level rose 10 meters due to the melting of all that ice – without any help from humans. New data suggests that the sea-level rise in the oceans took place over a few centuries, according to Hay. “You can lose most of the Greenland ice cap in a few hundred years, not thousands, just under natural conditions,” says Hay. “There’s no telling how fast it can go with this spike of carbon dioxide we are adding to the atmosphere.”
This possibility was brought home this last summer as Greenland underwent a stunning, record-setting melt. The ice streams, lubricated by water at their base, are speeding up. Hay notes, “Ten years ago we didn’t know much about water under the Antarctic ice cap.” But it is there, and it allows the ice to move – in some places even uphill due to the weight of the ice above it. “It’s being squeezed like toothpaste out of a tube,” explains Hay. The one thing that’s holding all that ice back from emptying into the sea is the grounded ice shelves acting like plugs on bottles at the ends of the coastal glaciers. “Nobody has any idea how fast that ice will flow into the oceans once the ice shelves are gone.” Another missing feedback is the groundwater being mined all over the world to mitigate droughts. That water is ultimately added to the oceans (a recent visualization of this effect in the U.S. was posted by NASA’s Earth Observatory.
All of these are positive feedbacks speeding up the changes in climate and sea-level rise. “You would expect negative feedbacks to creep in at some point,” says Hay. “But in climate change, every feedback seems to go positive.” The reason is that Earth’s climate seems to have certain stable states. Between those states things are unstable and can change quickly. “Under human prodding, the system wants to go into a new climate state.”
2012-11-05 21:24:48
Source: http://coyoteprime-runningcauseicantfly.blogspot.com/2012/11/global-warming-why-seas-are-rising.html