Wednesday, September 23, 2009

arctic sea ice reaches annual minimum

NSIDC | Arctic sea ice reflects sunlight, keeping the polar regions cool and moderating global climate. According to scientific measurements, Arctic sea ice has declined dramatically over at least the past thirty years, with the most extreme decline seen in the summer melt season.

Arctic sea ice appears to have reached its minimum extent for the year, the third-lowest extent since the start of satellite measurements in 1979. While this year’s minimum extent is above the record and near-record minimums of the last two years, it further reinforces the strong negative trend in summertime ice extent observed over the past thirty years.

Overview of conditions
On September 12, 2009 sea ice extent dropped to 5.10 million square kilometers (1.97 million square miles). This appears to have been the lowest point of the year, as sea ice has now begun its annual cycle of growth in response to autumn cooling. The 2009 minimum is the third-lowest recorded since 1979, 580,000 square kilometers (220,000 square miles) above 2008 and 970,000 square kilometers (370,000 square miles) above the record low in 2007.

The 2009 minimum is 1.61 million square kilometers (620,000 square miles) below the 1979 to 2000 average minimum and 1.28 million square kilometers (490,000 square miles) below the thirty-year 1979 to 2008 average minimum.

Conditions in context
This year, the minimum extent did not fall as low as the minimums of the last two years, because temperatures through the summer were relatively cooler. The Chukchi and Beaufort seas were especially cool compared to 2007. Winds also tended to disperse the ice pack over a larger region.

While the ice extent this year is higher than the last two years, scientists do not consider this to be a recovery. Despite conditions less favorable to ice loss, the 2009 minimum extent is still 24% below the 1979-2000 average, and 20% below the thirty-year 1979-2008 average minimum. In addition, the Arctic is still dominated by younger, thinner ice, which is more vulnerable to seasonal melt. The long-term decline in summer extent is expected to continue in future years.

Final analysis pending
In the beginning of October, NSIDC will issue a formal press release with full analysis of the melt season, and graphics comparing this year to the long-term record. We will also announce the monthly average September sea ice extent, the measure scientists rely on for accurate analysis and comparison over the long term. We will continue to post analysis of sea ice conditions throughout the year, with frequency determined by sea ice conditions. The near-real-time daily image update will continue each day.

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