What's Making Glaciers Melt Faster

The

earth’s climate is so complicated that science is still struggling to figure it out. That’s why — unlike something like, say, quantum physics — it’s hard to make accurate predictions about what will happen. So it came as no surprise, in a sense, that climate observers announced a huge surprise yesterday at the American Association for the Advancement of Science’s annual conference, in St. Louis: the glaciers of Greenland, which carry ice from the interior out to the sea, have gone on a tear. They’re flowing, on average, about twice as fast as they were a decade ago — and even back then, says glacier expert Julian Dowdeswell, of the University of Cambridge, "I was telling my students that they were among the fastest-flowing glaciers on Earth."

The apparent cause of this suddenly far from glacial flow rate is global warming — not because all of the ice itself is melting so fast, but because record melting at its upper surface is letting water percolate down to the bedrock, where it acts as a lubricant. Another factor, says Dowdeswell: ice "tongues" that form where glaciers meet the ocean have broken up over recent years, removing a sort of roadblock that holds them in check.

If all of Greenland’s ice were plopped into the ocean, sea level would rise a catastrophic 20 feet or more. Until yesterday, most experts thought global warming might make it happen in a couple of thousand years. Now they’re talking hundreds. It still sounds like a long time, but, says Michael Oppenheimer, a professor of geosciences and international affairs at Princeton, "that comes to a couple of feet per century, and that’s more than society is equipped to handle." It doesn’t, moreover, take into account the two mammoth ice sheets of Antarctica, which pack about 20 and 200 feet of potential sea-level rise, respectively, if some new process is discovered that speeds their disintegration. Given what’s being reported in Greenland, the fact that nobody knows what that process might be should be little comfort.

One interesting political note: Eric Rignot, the lead author of the Greenland study and an accompanying report in Science magazine, works for NASA’s Jet Propulsion Laboratory (the glaciers’ speedup was detected with a satellite). Just a couple of weeks ago, another NASA scientist named James Hansen claimed he’d been silenced by the agency for speaking out about evidence for global warming; the resulting furor led the NASA official who was involved to resign. Hansen’s commentary on the Greenland result appears here. And when Rignot was asked yesterday whether anyone at the agency had tried to shut him up, he said he’d been subjected to no such pressure.