Glacial ghosts set sea-level trap for East Coast

Paul Voosen in E&E News: The United States has a debt, etched in stone, to pay back to the sea. Across the world, the oceans are rising. Because of human-caused warming, global sea level has increased at 3 millimeters a year for the past two decades. Sucking in 90 percent of the excess heat trapped by greenhouse gases, the ocean is the world's thermometer, running hot. It's the largest sign, and impact, of climate change.

But as the surge sloshed into New York Harbor last week by Superstorm Sandy made clear, sea-level rise is also a deeply local phenomenon. There is no average ocean. There are only particular coastlines, shaped by geology, currents and gravity. The past matters. And in few places does it matter more than the United States.

Most of the country's eastern coastline is caught at the end of an unstoppable collapse, stemming from the loss of ice sheets many millennia ago. It's a complex process, with one succinct outcome: The ice age set a sea-level trap for the United States. From Massachusetts to the Carolinas, the Eastern Seaboard is sinking.

"[It's] going to experience significantly more sea-level rise than the global average," said Jerry Mitrovica, a geophysicist at Harvard University and expert on the continent's glacial legacy. "The U.S. East Coast could be at double the global average."...

The Greenland Ice Sheet from the air, shot by Hannes Grobe, Alfred Wegener Institute for Polar and Marine Research, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 2.5 Generic license