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Around the world, glaciers and polar ice sheets are shrinking. Scientists say a warmer atmosphere is the likely culprit. Now they're seeing some new and unexpected things happening that could make these great reservoirs of ice disappear even sooner. NPR's Christopher Joyce has more on glacial earthquakes and sliding ice sheets.
CHRISTOPHER JOYCE reporting:
Think glacial and you think, oh, waiting in line to renew your drivers license. But recently scientists discovered that glaciers can lurch suddenly and cause earthquakes. The man who discovered this, seismologist Göran Ekström at Harvard University, now says glaciers have been causing quakes in Greenland since 1993 and maybe longer.
Mr. GÖRAN EKSTRÖM (Seismologist, Harvard University): What we think is happening is that a piece of the glacier the size of Manhattan and the height of the Empire State Building moves forward about two cab lengths. It's pretty huge.
JOYCE: Not a huge quake, say, for California, maybe a magnitude five or so, but nothing to sneer at for a glacier. What's important here though is that the quakes are a symptom of some big changes in Greenland's vast ice sheet. It starts with increasingly warmer air temperatures melting ice on top. Then, says Ekström...
Mr. EKSTRÖM: Occasionally, that water on top of the ice drains to the bottom of the glacier and we believe that that water at the bottom of the glacier lubricates the sliding of the glacier.
JOYCE: Scientists already know that glaciers normally slide down their channels toward the ocean. But it's a slow regular slide. Now they're sliding twice as fast, at least in Greenland. And there are a lot more quakes.
Mr. EKSTRÖM: It is a very dramatic increase. We've seen a doubling in the number of these events over a period of maybe three or four years.
JOYCE: Writing in the Journal of Science, Ekström says most of the quakes are in the summer when there's more melt water. Glaciologists like Ian Joughin from the University of Washington expected more melting as the earth's atmosphere warms. But he says the faster sliding is curious and it's happening sooner then expected.
Mr. IAN JOUGHIN(Glaciologist, University of Washington): Sort of textbook glaciology would predict that ice sheets response takes sort of hundreds of years to kick in. But what's significant about this paper and several other papers are that they're showing that the ice sheets can actually respond over just the course of a few years.
JOYCE: As more polar ice melts and runs into the oceans, sea level rises. Scientists calculate there's enough ice in Greenland to raise sea levels some 17 feet. There's even more ice at the bottom of the planet, in the Antarctic. Some glaciers and ice shelves there reach out into the sea along submerged valleys.
Robert Bindschadler, a glaciologist at NASA's Goddard's Space Flight Center, also writes in Science Magazine that there may be more warm water in the southern ocean now, and it could be working its way underneath those glaciers.
Dr. ROBERT BINDSCHADLER (Glaciologist, Goddard Space Flight Center): It races down along the bed of these valleys and gets to the base of the glacier, where it melts that ice at a very high rate, and it reduces the friction that holds that glacier back, allowing it to accelerate.
JOYCE: As the glacier accelerates, more ice breaks off at the lip, or front. Think of toothpaste coming out of a tube, except in this case, its giant icebergs getting dumped into the ocean. The faster that happens, says Bindschadler, the faster sea level will rise.
Christopher Joyce, NPR News.
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