The lowest four Arctic wintertime maximum sea ice extents in the 39 years of satellite records have all occurred in the last four years. Photo by Nathan Kurtz/NASA
March 23 (UPI) -- The maximum extent of the Arctic's wintertime sea ice, reached last week, marked another historic low. According to the latest analysis, it was the second lowest since satellites began tracking the phenomenon 39 years ago.
Every year, the Arctic's sea ice grows in the winter and shrinks in the summer, reaching two extents, a maximum and a minimum. In recent years, both extents have been increasingly small.
Just ahead of the official end of winter, the Arctic sea ice reached its maximum extent on March 17, a grand total of 5.59 million square miles, 448,000 fewer square miles miles than the average maximum extent measured between 1981 and 2001.
This year's maximum extent measure just 23,200 more square miles than last year's record low maximum extent.
The four smallest maximum extents on record have occurred during the last four years.
Scientists at NASA and the National Snow and Ice Data Center use satellite observations to precisely measure the surface area of the Arctic's sea ice throughout the year, calculating monthly averages in addition to annual maximum and minimum extents.
"The Arctic sea ice cover continues to be in a decreasing trend and this is connected to the ongoing warming of the Arctic," Claire Parkinson, senior climate scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, said in a news release. "It's a two-way street: the warming means less ice is going to form and more ice is going to melt, but also, because there's less ice, less of the sun's incident solar radiation is reflected off, and this contributes to the warming."
Scientists at the NSIDC suggest the reduced ice coverage across the Bering Sea and Barents Sea can be explained by an especially late autumn freeze-up, in addition to high air temperatures throughout the winter.
Climate models suggest global warming has been most pronounced at Earth's poles, and the latest findings confirm as much. The melting of Arctic sea ice does not directly contribute to sea level rise. However, the absence of sea ice can leave Greenland's glaciers vulnerable to additional melting, and the same warming trends that have triggered the loss of sea ice is believed to be driving the destabilization of glaciers across the globe, ensuring seas will continue to rise well into the next century.