Floating ice, like the kind that covers the Arctic Ocean in wintertime and comprises ice shelves, doesn’t raise sea levels. Ice comes in many forms, with different consequences when it melts. In the past few years, scientists have identified marine ice-cliff instability as a feedback loop that could kickstart the disintegration of the entire West Antarctic ice sheet this century - much more quickly than previously thought. “We need to know how fast it’s going to happen.” “Ice is only so strong, so it will collapse if these cliffs reach a certain height,” explains Kristin Poinar, a glaciologist at NASA’s Goddard Space Flight Center. Once they start to crumble, the destruction would be unstoppable. Ice gets so heavy that these taller cliffs can’t support their own weight. The ocean floor gets deeper toward the center of this part of Antarctica, so each new iceberg that breaks away exposes taller and taller cliffs. The bad news? There’s growing evidence that the Pine Island Bay glaciers collapsed rapidly back then, flooding the world’s coastlines - partially the result of something called “marine ice-cliff instability.” To figure that out, scientists have been looking back to the end of the last ice age, about 11,000 years ago, when global temperatures stood at roughly their current levels. To support our nonprofit environmental journalism, please consider disabling your ad-blocker to allow ads on Grist. For that reason, finding out how fast these glaciers will collapse is one of the most important scientific questions in the world today. (A Rolling Stone feature earlier this year dubbed Thwaites “ The Doomsday Glacier.”) Together, they act as a plug holding back enough ice to pour 11 feet of sea-level rise into the world’s oceans - an amount that would submerge every coastal city on the planet. The glaciers of Pine Island Bay are two of the largest and fastest-melting in Antarctica. There’s no doubt this ice will melt as the world warms. Further inland, the glaciers widen into a two-mile-thick reserve of ice covering an area the size of Texas. Stretching across a frozen plain more than 150 miles long, these glaciers, named Pine Island and Thwaites, have marched steadily for millennia toward the Amundsen Sea, part of the vast Southern Ocean. In a remote region of Antarctica known as Pine Island Bay, 2,500 miles from the tip of South America, two glaciers hold human civilization hostage.
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