Sea ice coverage down by 278,000 square miles

Posted by Wolfgang Gruener

Washington, D.C. – Earlier today we learned about the massive retreat of glaciers in Antarctica and now we are hearing from NASA that average Arctic sea ice coverage is decreasing at a stunning pace. Thin seasonal ice – ice that melts and re-freezes every year - now makes up about 70% of arctic ice in the winter, up from only 40 to 50% in the 1980s and 1990s.

Scientists who track Arctic sea ice cover from space announced today that this winter had the fifth lowest maximum ice extent on record. According to data published by the National Snow and Ice Data Center, the maximum sea ice extent for the 2008 to 2009 period was reached on February 28 at 5.85 million square miles. This number is down about 4.5% from an average of more than 6.13 million square miles that was recorded between 1979 and 2000, NASA said.

The 278,000 square mile decrease in coverage compares to the size of California and Arizona combined.

NASA’s satellites also found that the share of Arctic thin ice is growing quickly and that sea ice that survives at least one summer is increasingly rare. Ice that melts and re-freezes every year makes up about 70% of the Arctic sea ice in wintertime, up from 40 to 50% in the 1980s and 1990s. Thicker ice, which survives two or more years, now represents just 10% of wintertime ice cover, down from 30 to 40%. Seasonal thin ice averages about 6 feet in thickness, while ice that had lasted through more than one summer averages about 9 feet, NASA said.

"Ice extent is an important measure of the health of the Arctic, but it only gives us a two-dimensional view of the ice cover," said Walter Meier, research scientist at the National Snow and Ice Data Center and the University of Colorado, Boulder. "Thickness is important, especially in the winter, because it is the best overall indicator of the health of the ice cover. As the ice cover in the Arctic grows thinner, it grows more vulnerable to melting in the summer."

NASA explained that Arctic sea ice works like an air conditioner for the global climate system. Ice naturally cools air and water masses, plays a key role in ocean circulation, and reflects solar radiation back into space. The Arctic ice cap grows each winter as the sun sets for several months and intense cold sets in. Some of that ice is naturally pushed out of the Arctic by winds, while much of it melts in place during summer. The thicker, older ice that survives one or more summers is more likely to persist through the next summer.

Sea ice thickness has been hard to measure directly, so scientists have typically used estimates of ice age to approximate its thickness. Last year, a team of researchers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., produced the first map of sea ice thickness over the entire Arctic basin. Equipped with two years of data provided by NASA's Ice, Cloud, and land Elevation Satellite (ICESat), the JPL team discovered that the average winter volume of Arctic sea ice contained enough water to fill Lake Michigan and Lake Superior combined.