ARTIC (24 Sep 2003) -- The largest ice shelf in the Northern Hemisphere has broken in two, draining a freshwater lake beneath the ice and providing further evidence of climate change in the Earth's Arctic reaches, scientists said yesterday. The researchers said a fissure appeared in the Ward Hunt Ice Shelf in 2000 and it was cleaved completely by the following year. In 2002, the original fissure had widened to 85 yards in some spots, many other fissures had opened and a 2.4-mile-square area of free-floating ice blocks had appeared. "We believe that these events fit into a bigger picture of climate [warming] in the Arctic," said geophysicist Martin O. Jeffries of the University of Alaska at Fairbanks. "There is growing evidence of Arctic-wide warming in the last 10 to 15 years." Jeffries joined the team of researchers led by Warwick F. Vincent and Derek R. Mueller of Laval University in Quebec. The Ward Hunt Shelf was the largest remaining piece of an ice shelf that a century ago rimmed the entire northern coast of Canada's Ellesmere Island, the northernmost land mass in North America, the researchers said in an upcoming article in Geophysical Research Letters. By 1982, about 90 percent of the shelf was gone, but melting and breakup appeared to stabilize for the next 20 years, the article said. Then, in April 2000, Canadian satellite images showed the beginnings of cracking from the eastern side of Ward Hunt Island into 20-mile long Disraeli Fjord. The ice shelf had served to dam fresh water trapped beneath the fjord's surface ice. The fissure had breached the shelf, however, draining the lake, the scientists said. | | Weather stations in the Canadian Arctic have recorded average temperature increases of about four-tenths of a degree Fahrenheit every decade since 1967, a dramatic change that has raised the average July temperatures on the Ward Hunt shelf slightly above freezing. That causes puddles to form on the ice sheet, which are darker in color than the ice itself and absorb heat more readily, noted Kevin E. Trenberth, a senior scientist at the National Center for Atmospheric Research in Denver. "Once the puddles are started, the melting can accelerate very rapidly." Jeffries said, "It has been accepted for some time that should the global climate start to warm, the effects would be felt first in the polar regions, and they would be amplified. This could be part of that signal." Trenberth and others cautioned that the current rise probably has more to do with long-term world climate patterns than with the release of carbon dioxide and other greenhouse gases because of modern-day human activities. "But even though this ice melt and permafrost thawing is happening too fast to be due to global warming, this is the kind of prototype of what we should expect after the next few decades," added atmospheric chemist Ralph J. Cicerone of the University of California at Irvine. "This is a good dress rehearsal for the kinds of things we could see later. SOURCE - Washington Post |
