Thursday, November 12, 2015

Past the point of no return

It won’t take much to cause the entire West Antarctic Ice Sheet to collapse—and once it starts, it won’t stop. In the last year, a slew of papers has highlighted the vulnerability of the ice sheet covering the western half of the continent, suggesting that its downfall is inevitable—and probably already underway. Now, a new model shows just how this juggernaut could unfold. A relatively small amount of melting over a few decades, the authors say, will inexorably lead to the destabilization of the entire ice sheet and the rise of global sea levels by as much as 3 meters.

Previous models have examined the onset of the collapse in detail. In 2014, two papers, one in Science and one in Geophysical Review Letters, noted that the Thwaites Glacier, which some scientists call the “weak underbelly” of the West Antarctic Ice Sheet, has retreated dramatically over the past 2 decades. Most Antarctic researchers chalk this up to warm seawater melting the floating ice shelves at their bases; seawater temperatures there have risen since the 1970s, in part because of global temperature increases. Right now, an underwater ledge is helping anchor the glacier in place. But when the glacier retreats past that bulwark, it will collapse into the ocean; then seawater will intrude and melt channels into the ice sheet, setting the juggernaut in motion.

And we haven't even talked about the Greenland equation. Click albedo effect to see how disappearing ice transforms the uncovered ocean into a heat sink, thus helping to push the state of GW past the point of no return.

Region where collapse is imminent.

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