The National Snow and Ice Data Center (NSIDC) has tentatively announced that Arctic sea ice has reached its minimum extent for the year. From the NSIDC release:
The blanket of sea ice that floats on the Arctic Ocean appears to have reached its lowest extent for the year. Arctic sea ice extent fell to 4.33 million square kilometers (1.67 million square miles) on September 9, 2011. This year’s minimum was the second lowest in the satellite record, which started in 1979. The lowest extent was recorded in 2007.Over the last thirty years, ice extent, a two-dimensional measure of the ice cover on the Arctic Ocean, has declined in all months, with a more pronounced drop in summer. Scientists attribute this decline in large part to climate change. Arctic sea ice melts and refreezes in an annual cycle, reaching its lowest point in late summer, and its highest point in late winter.
Meanwhile, NASA Goddard Space Flight Center has posted HD video of the decline from the near maximum ice extent in early spring of 2011 through Sept. 9, 2011. The visualization (above) is based on data collected by Aqua’s AMSR-E instrument. From Goddard’s Flickr caption:
Sea ice goes through this shrink-and-swellrhythm every year, but since consistent satellite observations began in1979, both the annual minimum at the end of summer and the annualmaximum at the end of winter continue to decline in area and thickness.Consistent with rising temperatures globally and specifically in theArctic, climate scientists are concerned with this trend both as anindicator of climate change and as a feedback mechanism. As the white,highly reflective ice disappears, darker ocean waters appear. Thisdarker surface absorbs more solar radiation and acts as a positivefeedback to the warming that is already occurring and causing the changein the first place.