The pink line shows the 1979–2000 average.
March 2007 ice extent is the solid off-white.
Land masses are green; water is dark blue.
Source: NSIDC Sea Ice Index
The maximum reach of Arctic sea ice during the 2007 winter was the second smallest since satellite coverage began, only 1.7 percent larger than minimum record set in March 2006, according to the National Snow and Ice Data Center.
The area of ocean covered with at least 15 percent ice was only 5.7 million square miles (14.7 million square kilometers) during March — compared to 5.6 million square miles seen in March 2006, said a NSIDC report published online this week.
Sea ice has been declining 5 to 7 percent per decade for a generation in a meltdown that has seen record or near record minimums every month since 2000. Scientists blame a combination of natural cycles, Arctic warming and dramatic shifts in ocean and air currents — old ice has been flushed out into the Atlantic and warm ocean water has pulsed north. (See FNS story Arctic ice: the shrink goes on for more details and sea ice links.)
“This year’s low wintertime extent is another milestone in a strong downward trend,” said NSIDC scientist Walt Meier. “We’re still seeing near-record lows and higher-than-normal temperatures. We expect the downward trend to continue in future years.”
To put it into perspective, the average ice cover for March between 1979 and 2000 has been about 6.1 million square miles. As of last month, a frozen floating habitat one-and-half times the size of Texas has simply vanished from the Far North.
Tracking the “recovery” of the winter ice pack gives scientists a fix on what might happen during the summer. It’s the winter chill that manufactures the sea ice and grows existing ice, creating the vast habitat for marine mammals like polar bears and providing the planet with one of its engines for regulating global temperature.
Less ice in March — the climax of the freezing season — can mean another immense loss during the summer. Last March’s record minimum was followed in September by the second lowest ice extent ever recorded.
NSIDC’s Stephanie Renfrow explains:
Scientists monitor the sea ice year-round, paying special attention to extent during March and September. March usually marks the end of winter in the Arctic, a period when sea ice grows, or recovers, from the summer minimum.
Low winter recovery means that the ice is freezing up later in the fall and growing at a slower pace in the winter. September usually marks the end of the summer melting season; low summer extent means that ice is melting faster during the summer and leaving less ice to build on during winter recovery.