Satellite imagery shows the melting is happening much faster than climate models had predicted.
The amount of sea ice in the Arctic Circle has shrunk to a new low, scientists have discovered - providing more evidence of global warming, but also raising the prospect of new northern shipping routes and exploration for oil.
The melting is happening faster than computer models had predicted, according to the scientists at the federally supported National Snow and Ice Data Center at the University of Colorado at Boulder.
At this rate, a complete melting of Arctic sea ice could happen by 2030 - far sooner than expected.
"We've been seeing this loss of ice. What has greatly surprised us is how quickly we are losing it," said Mark Serreze, senior research scientist at the center, who led a team of six
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analyzing new satellite imagery received Friday.
"This is telling us the Arctic is on a fast-track of change. It may well be unstoppable ...," Serreze said. "The numbers that come to us day-to-day leave us agog, ... somewhat blue, yes. This is disturbing stuff we are seeing."
Arctic sea ice keeps polar regions cool and helps control the global climate, reflecting sunlight back into space. As the ice melts in summer, oceans heat up. Scientists at the center here in Colorado measure the amount of sea ice using imagery from U.S. Department of Defense satellites delivered by NASA. The National Oceanic and Atmospheric Administration and National Science Foundation support the monitoring.
Five years ago, 2070 was thought to be the soonest a total summer meltdown was possible, based on the computer modeling scientists worldwide use to try to anticipate global climate change.
New Arctic sea ice still will form in the winter, though it may be thinner than before. Scientists said they think Arctic ice seems to be melting more in summer and growing back less in winter.
New data received Friday showed 2.02 million square miles of ice in the Arctic. That's significantly less than the previous minimum of 2.05 million square miles measured on Sept. 21, 2005.
Arctic ice normally melts into October. Scientists said much more ice is likely to melt before temperatures drop. The ice appeared to have thinned most on the Siberian side of the Arctic, where Russian oil exploration has increased, and north of Alaska and Canada.
Ships now move more easily in some northern areas, though no major route from the Pacific to the Atlantic has opened. The ice hadn't shrunk as much on the Atlantic side, according to the data.
Some scientists say climate changes may be the result of natural fluctuations, but a growing number point to intensifying human industrial activity that releases greenhouse gases into the atmosphere as a driving cause.
"We lose that sea ice, that refrigerator in the Arctic, and we can start to have impact down in the mid-latitudes, including Colorado - on agriculture, on the ski industry," said the center's Serreze, a climate specialist who has been studying the Arctic for 25 years.
"Just how it will pan out, we don't know. It's not so much what we know that concerns me. It's what we don't know."