This year's sea ice extent is substantially higher than last year's record low minimum. On Sept.16, 2012, Arctic sea ice reached its smallest extent ever recorded by satellites at 1.32 million square miles (3.41 million square kilometers). That is about half the size of the average minimum extent from 1981 to 2010.
This summer's minimum is still the sixth lowest extent of the satellite record and is 432,000 square miles (1.12 million square kilometers) lower than the 1981-2010 average, roughly the size of
The 2013 summertime minimum extent is in line with the long-term downward trend of about 12 percent per decade since the late 1970s, a decline that has accelerated after 2007. This year's rebound from 2012 does not disagree with this downward trend and is not a surprise to scientists.
"I was expecting that this year would be higher than last year," said
The ice cap covering the
This year, Arctic temperatures were 1.8 to 4.5 ° Fahrenheit (1 to 2.5 degrees Celsius) lower than average, according to
"The trend with decreasing sea ice is having a high-pressure area in the center of
The remaining Arctic sea ice cover is much thinner on average than it was years ago. Satellite imagery, submarine sonar measurements, and data collected from
Most of the
"Thinner ice melts completely at a faster rate than thicker ice does, so if the average thickness of Arctic sea ice goes down, it's more likely that the extent of the summer ice will go down as well," said
Comiso added that the slight rebound in the 2013 sea ice minimum extent is consistent with a rebound in the multiyear ice cover observed last winter.
"The character of the ice is fundamentally different: It's thinner, more broken up, and thus more susceptible to melt completely," Meier said. "This year, the cool temperatures saved more of the ice. However, the fact that as much of the ice melted as it did is an indication of how much the ice cover had changed. If we had this weather with the sea ice of 20 years ago, we would have had an above-normal extent this year."
The sea ice minimum extent analysis produced at NASA Goddard - one of many satellite-based scientific analyses of sea ice cover - is compiled from passive microwave data from
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