Monday, June 05, 2017

How Is Worldwide Sea Level Rise Driven by Melting Arctic Ice?

I get the print edition of Scientific American at my local Barnes and Noble store.

Read the print article or the link below for additional ways warming temperatures cause sea level rise.

Experts explain how land ice thaw and the dynamics of warming water are raising ocean levels
By Annie Sneed on June 5, 2017

Climate change is warming the Arctic more than twice as fast as anywhere else on the planet. One of the most serious consequences is sea level rise, which threatens nations from Bangladesh to the U.S. But exactly how does melting Arctic ice contribute to sea level rise? Scientific American asked Eric Rignot, professor of earth system science at the University of California, Irvine, and Andrea Dutton, assistant professor of geology at the University of Florida, how changes in this particular northern region are driving the oceans to dangerous heights.

Seas are now rising an average of 3.2 millimeters per year globally, and are predicted to climb a total of 0.2 (7.9 in) to 2.0 meters (6.5 feet) by 2100. Rignot and Dutton say that in the Arctic, the Greenland Ice Sheet poses the greatest risk for ocean levels because melting land ice is the main cause of rising seas—and “most of the Arctic’s land ice is locked up in Greenland,” Rignot explains. That’s 2.96 million cubic kilometers of ice now covering land areas—and it’s melting into the ocean. If the entire Greenland Ice Sheet thawed, Dutton says, it would raise sea levels by an average of seven meters (23 feet). That would significantly flood coastal megacities such as Mumbai and Hong Kong.

Greenland’s land ice is already thawing fast enough to raise worldwide seas 0.74 millimeter per year. “The melt rate has been increasing,” in large part because the ice sheet’s surface thawing has picked up as global temperatures warm, Dutton says. “This acceleration of surface melt has doubled Greenland’s contribution to sea level rise” compared with the period from 1992 to 2011, Dutton adds.


In addition to simply adding water to the ocean, thawing Arctic land ice can raise sea levels even more via a mechanism called thermal expansion. “In a warmer climate the ocean absorbs a lot of extra heat from the climate system, and as a result it becomes less dense,” Rignot explains. As Arctic land ice melts into the sea, there is more ocean water overall—and thus more water to heat up and expand as the climate warms, which drives up sea levels even more. “The amount it expands is significant, enough that we can measure it,” Dutton says. From 1993 to 2010 thermal expansion added an average of 1.1 millimeters of sea level rise per year, according to the International Panel on Climate Change Fifth Assessment Report.


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