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Chapter Four Excerpt: The Hell and High Water Scenario

We could get a meter [of sea-level rise] easy in 50 years.

— Bob Corell, chair, Arctic Climate Impact Assessment, 2006

The peak rate of deglaciation following the last Ice Age was . . . about one meter [39 inches] of sea- level rise every 20 years, which was maintained for several centuries.

— James Hansen, director, Goddard Institute for Space Studies (NASA), 2004

Sea-level rise of 20 to 80 feet will be all but unstoppable by midcentury if current emissions trends continue. The first few feet of sea-level rise alone will displace more than 100 million people worldwide and turn all of our major Gulf and Atlantic coast cities into pre-Katrina New Orleans — below sea level and facing superhurricanes.

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Sea-level rise is a lagging indicator of climate change, in part because global warming also increases atmospheric moisture. More atmospheric moisture probably means more snowfall over both the Greenland and Antarctica ice sheets, which would cause them to gain mass in their centers even as they lose mass at the edges. Until recently, most scientists thought that the primary mechanism by which these enormous ice sheets would lose mass was through simple melting. The planet warms and ice melts — a straightforward physics calculation and a very slow process, with Greenland taking perhaps a thousand years or more to melt this way, according to some models.

Since 2001, however, a great many studies using direct observation and satellite monitoring have revealed that both of the two great ice sheets are losing mass at the edges much faster than the models had predicted. We now know a number of physical processes can cause the major ice sheets to disintegrate faster than by simple melting alone. The whole idea of “glacial change” as a metaphor for change too slow to see will vanish in a world where glaciers are shrinking so fast that you can actually watch them retreat.

The disintegration of the Greenland and Antarctic ice sheets is a multistage process that starts with the accelerated warming of the Arctic….