Sep 28, 2007
Arctic sea ice coverage hits a new low
Scientists from the National Snow and Ice Data Centre (NSIDC) in Boulder, US, claim that the extent of Arctic sea ice reached its minimum for 2007 on September 16, shattering all previous lows since satellite record-keeping began nearly 30 years ago.
The Arctic sea ice extent on September 16 stood at 1.59 million square miles, or 4.13 million square kilometres, as calculated using a five-day running average, according to the team. Compared to the long-term minimum average from 1979 to 2000, the new minimum extent was lower by about 1 million square miles – an area about the size of Alaska and Texas combined, or 10 United Kingdoms.
The minimum for 2007 shatters the previous five-day minimum set on September 20–21, 2005, by 1.19 million square kilometers (460,000 square miles), roughly the size of Texas and California combined, or nearly five United Kingdoms.
"The amount of ice loss this year absolutely stunned us because it didn't just beat all previous records, it completely shattered them," said CU-Boulder senior scientist Mark Serreze of NSIDC.
The sea ice extent is the total area of all Arctic regions where ice covers at least 15% of the ocean surface.
Scientists blame the declining Arctic sea ice on rising concentrations of greenhouse gases that have elevated temperatures from –16 °C to –14°C across the Arctic, and strong natural variability in Arctic sea ice, said the researchers.
The CU–Boulder research group said determining the annual minimum sea ice is difficult until the melt season has decisively ended. But the team has recorded five days of little change, and even slight gains in Arctic sea ice extent this September, so reaching a lower minimum for 2007 seems unlikely.
Arctic sea ice generally reaches its minimum extent in September and its maximum extent in March. The researchers used satellite data from NASA, the National Oceanic and Atmospheric Administration and the US Department of Defense, as well as data from Canadian satellites and weather observatories for the study.
Arctic sea ice keeps the polar regions cool and helps moderate global climate. Sea ice has a bright surface, so 80% of the sunlight that strikes it is reflected back into space. As sea ice melts in the summer, it exposes the dark ocean surface. Instead of reflecting 80% of the sunlight, the ocean absorbs 90% of the sunlight. The oceans heat up, and Arctic temperatures rise further.