WASHINGTON (AP) — Critical ice in the Arctic Ocean melted to record low levels this sweltering summer and that can make weather more extreme far away from the poles, scientists say.
The National Snow and Ice Data Center reported Monday that the extent of Arctic sea ice shrank to 1.58 million square miles and is likely to melt more in the coming weeks. That breaks the old record of 1.61 million square miles set in 2007.
The North Pole region is an ocean that mostly is crusted at the top with ice. In the winter, the frozen saltwater surface usually extends about 6 million square miles, shrinking in summer and growing back in the fall. That's different from Antarctica, which is land covered by ice and snow and then surrounded by sea ice.
Normally sea ice in the Arctic reaches its minimum in mid-September and then starts refreezing. But levels on Sunday shrank 27,000 square miles — about the size of West Virginia — beyond the old record.
Figures are based on satellite records dating back to 1979. The ice center bases its figures on averages calculated over five days.
Data center scientist Ted Scambos said the melt can be blamed mostly on global warming from man-made emissions of greenhouse gases. There are natural factors involved too, including a storm that chewed up a significant amount ice earlier this month. But, he said, dramatic summer sea ice losses in all but one year since 2007, continuous thin ice, and warm air temperatures show a pattern that can only be explained by climate change.
"It really does imply that the Arctic is moving to a new state," said NASA ice systems program scientist Tom Wagner. "The Arctic is changing."
Wagner and Scambos said in 2007 some people thought it was just an odd year that caused the dramatic melt, but years like this one show something bigger is happening.
This milestone is a "substantial step" to the day when there will be no significant sea ice in the Arctic in the summer, said NASA chief scientist Waleed Abdalati.
"Why do we care?," Abdalati, an ice scientist, asked. "This ice has been an important factor in determining the climate and weather conditions under which modern civilization has evolved."
Scientists sometimes call the Arctic the world's refrigerator and this is like leaving the fridge door open, Scambos said.
"This is kind of a knob on global weather," Wagner said. "We don't know the impact yet" of fiddling with it.
Scientists say Arctic sea ice helps moderate temperatures further south in the winter and summer. A study earlier this year in the peer-reviewed journal Geophysical Research Letters linked some of the factors behind Arctic sea ice loss to higher probabilities of extreme weather "such as drought, flooding, cold spells and heat waves."
Scientists also say sea ice is crucial for polar bears and other animals.
Wagner said the changes in Arctic sea ice fits with glacier loss in Alaska and Canada and ice loss in Greenland. Earlier this summer, NASA satellites reported a dramatic melt in Greenland, where nearly every part of its massive ice sheet started melting, something that last happened in 1889.
Ohio State University ice scientist Jason Box has been monitoring Greenland, where he said temperatures have sometimes been 9 to 18 degrees warmer than normal this summer and the ice is reflecting far less heat — and thus absorbing more energy — than ever before.
Global warming physics for years has been saying if greenhouse gases are causing climate change, the Arctic will feel it first with loss of sea ice and melt in snow and ice on land, Box said.
"We're in a declining trend because the Earth is getting warmer," Scambos said. "It's going to continue to be a series of shrinking ice extents year by year... We're not going back."
National Snow and Ice Data Center: http://nsidc.org/arcticseaicenews/
Seth Borenstein can be followed at http://twitter.com/borenbears