Warming in the Arctic shrank the ice covering the polar ocean this year to its second-lowest extent in four decades, scientists announced Monday, yet another sign of how climate change is rapidly transforming the region.

Satellites recorded this year's sea ice minimum at 3.74 million square kilometers on Sept. 15, only the second time the ice has been measured below 4 million square kilometers in 40 years of record keeping, said researchers at the National Snow and Ice Data Center (NSIDC).

"It's fairly devastating that we've had such consistently low sea ice. But unfortunately, it's not surprising," said Twila Moon, a glaciologist at the research center in Boulder, Colorado.