The Envisat satellite measures trace gases in the atmosphere as well as temperature of the sea surface. What it found was that in March of this year the levels of ozone over the Arctic, especially over the area between northwestern Russia and Greenland, were much lower than they were the previous year. Ozone levels were down in 1997, which was also an exceptionally cold winter. But the levels measured in 2011 were a record, according to the ESA."
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