How a melting ice sheet could actually lower sea level in some places

NASA Goddard Space Flight Center/Flickr (CC BY 2.0)

How a melting ice sheet could actually lower sea level in some places

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WASHINGTON, D.C.The Greenland ice sheet is melting. If you live in nearby Norway, how worried should you be about that sudden influx of water flooding your house? It turns out, not nearly as worried as you should be if you live in Chile. People tend to imagine that when an ice sheet melts, it adds water to all of the world’s ocean uniformly, like a bathtub filling up. “That isn’t even close,” Harvard University geophysicist Jerry Mitrovica told attendees yesterday at the annual meeting of AAAS (which publishes Science) in Washington, D.C. “Each ice sheet has its own pattern of sea level rise.” Mitrovica mapped what would happen to the world’s ocean if the rapidly melting Greenland ice sheet collapsed (as seen above). Right now, that ice is a huge weight pushing down Earth’s crust in and around Greenland. So when it’s gone, that land will pop up. An intact ice sheet also has a noticeable gravitational pull, which attracts water to the region. No ice means that water will rush away. Both of those effects actually add up to lower sea levels in the area right around the former ice sheet, Mitrovica said. When Greenland melts, places as far away as Norway and Scotland could actually see the sea level fall by as much as 50 meters. “But you pay the price somewhere,” Mitrovica said. In the Southern Hemisphere, you get more [sea level rise] than you bargained for.” The same counterbalancing effect holds for the West Antarctic Ice Sheet. If it were to collapse, the seas would rise the highest near Washington, D.C., and Northern California.

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