by Malte Humpert The extent and volume of Arctic sea ice were the lowest on record for the month of July according to data from the National Snow and ice Data Center and the Polar Science Center. July air temperatures over the North Pole were 11-14 degrees Fahrenheit above average for the first part of the month.
Arctic sea ice extent fluctuates seasonally. It typically starts declining at the end of March before recovering with the onset of Arctic winter in late September.
The all-time low occurred in September 2007, however, 2011 is on pace to break that record. Average ice extent for July 2011 fell to 7.92 million sq km, more than 200,000 sq km below the previous record low from four years ago. Including 2011 ice has declined by 6.8% per decade since 1979.
The decline of ice volume has progressed even faster. Mean sea ice volume since 1979 ranges from 28,700 cu km in April to 12,300 cu km in September. July 2011 set a new record low, 51% below the mean for that month and 62% below the maximum in 1979. New measurements show a rapid decline in oldest and thickest ice. The so-called multi-year ice which survives the melting of the summer months refreezes during the winter.
Age and thickness matter to the overall stability of the ice. Older ice grows stronger over the years while newly formed first year ice is most vulnerable.
The Northwest Passage, along Canada's northern coast, remains choked with ice. According to the National Snow and ice Data Center, however, old ice, which had previously survived throughout the Canadian Archipelago, has declined at 16% between March and July.
The 2011 minimum sea ice extent is expected around September 23rd. Although coverage recovered slightly during the last 10 days of July, 2011 is forecasted to set a new record low.
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