Arctic sea ice extent as observed by Envisat

September 2007 saw a low sea ice extent record in Arctic with 4.10 million km² . September 2010 is the third low sea ice extent record with 4.60 million km²  and 2011 shows a comparable low record than 2007. This has been seen by several sensors onboard satellites, the altimeter on Envisat among others. Indeed, for the first time in 2007, an altimetry satellite has measured open water sea surface height North East Siberia up to 82° during September.

The decrease of the sea ice extent is a problematic phenomena since the ice reflects the sun energy. Without ice, the sun radiations are absorbed by the ocean, thus increasing the warming.

Monthly sea ice coverage averaged in 1°x1° boxes over September 2007 (left) September 2010 (middle) and September 2011 (right) derived from RA-2 data. White area is open water. (Credits CLS).

Daily Arctic sea ice extent derived from microwave measurements on September 16, 2007 (left) and September 19, 2010 (right). The pink and orange line show the 1979 to 2000 median extent for these days. Credits National Snow and Ice Data Center.

Sea ice coverage averaged in 1°x1° boxes over September 2007 with respect to a mean over the previous years (2003-2006) derived from RA-2 data. Dark blue is open water (0), White (2) is the ice in September as usual; light blue (1) shows where ice has been observed previously and is not in 2007. (Credits CLS)

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