麻豆av在线看,欧美黑人猛交,在线播放国产精品,亚洲欧洲日产专区,国产精品国产三级国产专播i12

Slides
Photos

Fast-melting glaciers puzzle scientists

(China Daily)
Updated: 2009-09-16 11:41

University of Maine glaciologist Gordon Hamilton and graduate student Kristin Schild working on a GPS receiver tracking the flow speed of Helheim Glacier in southeast Greenland last month. Like Greenland's other major glaciers, it accelerated earlier this decade, contributing to the melt of the ice sheet and sea-level rise. [Agencies]

HELHEIM GLACIER, Greenland: Suddenly and without warning, the gigantic river of ice sped up, causing it to spit icebergs ever faster into the ocean off southeastern Greenland.

The Helheim Glacier nearly doubled its speed in just a few years, flowing through a rift in the barren coastal mountains at a stunning 30 meters (100 feet) per day.

Alarm bells rang as the pattern was repeated by glaciers across Greenland: Was the island's vast ice sheet, a frozen water reservoir that could raise the sea level six meters if disgorged, in danger of collapse?

Half a decade later, there's a little bit of good news and a lot of uncertainty.

"It does seem that the very rapid speeds were only sustained for a short period of time, although none of these glaciers have returned to the 'normal' flow speeds yet," says Gordon Hamilton, a glaciologist from the University of Maine who has clocked Helheim's rapid advance using GPS receivers on site since 2005.

Understanding why Greenland's glaciers accelerated so abruptly in the first half of the decade - and whether they are now slowing down - is crucial to the larger question of how fast sea levels will rise as the planet warms.

The issue has gained urgency as scientists rush to supply their latest findings in time for negotiations on a new global climate pact, set for December in Copenhagen.

Previous page 1 2 3 Next Page