Arctic Ice Minimum
The Arctic is especially vulnerable to the effects of global warming, as has become apparent in the melting sea ice in recent years. Climate models predict much greater warming in the Arctic than the global average, resulting in significant attention to the region. In particular, there are concerns that Arctic shrinkage, a consequence of melting glaciers and other ice in Greenland, could contribute to a substantial rise in sea levels worldwide. Arctic sea ice cover likely melted to its minimum extent for the year on September 16, according to scientists at the National Snow and Ice Data Center (NSIDC). Sea ice extent fell to 3.41 million square kilometers (1.32 million square miles), which is now the new lowest summer minimum extent.
"We are now in uncharted territory," said NSIDC Director Mark Serreze. "While we’ve long known that as the planet warms up, changes would be seen first and be most pronounced in the Arctic, few of us were prepared for how rapidly the changes would actually occur."
In September 2008, the extent of the summer Arctic ice cap was at a near-record low, only 9.01 percent greater than the record low in 2007, and 33.6 percent below the average extent of sea ice from 1979 to 2000. According to the University of Bremen, in September 2011 the Arctic ice cap was smaller than ever before recorded since the satellite measurements started in the 1970s. Arctic ice is declining in area and thinning. Arctic temperatures have risen more than twice as fast as the global average over the past half century.
Arctic sea ice cover grows each winter as the sun sets for several months, and shrinks each summer as the sun rises higher in the northern sky. Each year, the Arctic sea ice reaches its minimum extent in September. This year’s minimum follows a record-breaking summer of low sea ice extents in the Arctic. Sea ice extent fell to 4.10 million square kilometers (1.58 million square miles) on August 26, breaking the lowest extent on record set on September 18, 2007 of 4.17 million square kilometers (1.61 million square miles). On September 4, it fell below 4.00 million square kilometers (1.54 million square miles), another first in the 33-year satellite record.
"The strong late season decline is indicative of how thin the ice cover is," said NSIDC scientist Walt Meier. "Ice has to be quite thin to continue melting away as the sun goes down and fall approaches."
NSIDC scientists have observed fundamental changes in the Arctic’s sea ice cover. The Arctic used to be dominated by multiyear ice, or ice that survived through several years. Lately, the Arctic is increasingly characterized by seasonal ice cover and large areas are now prone to completely melt away in summer.
Arctic sea ice has long been recognized as a sensitive climate indicator. The region’s sea ice extent--defined by NSIDC as the total area covered by at least 15 percent of ice—varies from year to year because of changeable weather conditions. However, ice extent has shown a dramatic overall decline over the past thirty years. This year’s minimum will be nearly 50 percent lower than the 1979 to 2000 average.
NSIDC lead scientist Ted Scambos said that thinning ice, along with early loss of snow, are rapidly warming the Arctic. "But a wider impact may come from the increased heat and moisture the warmer Arctic is adding to the climate system," he said.
NSIDC scientist Julienne Stroeve said, "Recent climate models suggest that ice-free conditions may happen before 2050, though the observed rate of decline remains faster than many of the models are able to capture."
Serreze said, "While lots of people talk about opening of the Northwest Passage through the Canadian Arctic islands and the Northern Sea Route along the Russian coast, twenty years from now from now in August you might be able to take a ship right across the Arctic Ocean."
For further information see Arctic Ice.
Arctic Sea image via Wikipedia.