After several weeks reporting record lows of summer sea ice in Arctic seas, scientists this week noted that sea ice was starting to form again as fall approaches — but not before one more record low.
Sea ice freezes and melts seasonally, but never in 30 years of satellite records has it ebbed to this small a patch, the National Snow and Ice Data Center said in a statement Thursday.
"The amount of ice loss this year absolutely stunned us because it didn't just beat all previous records, it completely shattered them," Mark Serreze, a senior scientist at the center, said in the statement.
On Sept. 16, the sea ice extent
stood at 1.59 million square miles, or 4.13 million square kilometers, as calculated using a five-day running average. Compared to the long-term minimum average, that was lower by about 1 million square miles — an area the size of Alaska and Texas combined, the center said.
And compared to the previous end-of-season record, set on Sept. 21, 2005, "the Arctic has lost an area of sea ice the size of the states of Texas and California combined," or about 460,000 square miles, it added. That's more than double the drop between 2005 and 2002, the previous record-holding year.
'Really accelerating the trend'
"It's the biggest drop from a previous record that we've ever had and it's really quite astounding," said Walt Meier, a research scientist at the center in Boulder, Colo. "Certainly we've been on a downward trend for the last 30 years or so, but this is really accelerating the trend."
The minimum amount of ice occurred on Sunday and freezing has already begun in some places, according to satellite imagery used by the center.
Melting sea ice, unlike the melting glaciers of Greenland and Antarctica, does not contribute to global sea level rise, much as an ice cube in a glass of water does not make the level of liquid rise when it melts.
However, without the bright white of sea ice to reflect the sun's rays, the Earth loses what some climate scientists call its air conditioner. The less ice there is, the more dark water there is to absorb the warming solar radiation.
Less sea ice also means less habitat for polar bears. The Bush administration is now weighing whether to list the species as endangered due to habitat loss.
'Perfect storm' of factors
This year's record was caused by a "perfect storm" of interacting factors, Meier said. These included:
- A long-running high pressure system that kept skies cloudless over the Arctic.
- A circulation pattern that pushed ice out of the Arctic towards Greenland, instead of letting it circle around the Beaufort Sea north of Alaska as it usually does.
- Also, there was thinner ice to begin with.
While this particular year's ice minimum cannot be directly attributed to anthropogenic, or human-caused, global climate change, the trend that brought it about can, he said.
"This year, the reason why (the ice) was so low was not because there's more anthropogenically generated carbon dioxide dumped in the last year, it's because of this high pressure ... but you can't really explain the overall trend without invoking anthropogenically global warming," Meier said.
He also noted that the decrease in Arctic sea ice was forecast in models used by the U.N. Intergovernmental Panel on Climate Change, which this year said with 90 percent probability that global warming exists and that human activities contribute to it.
However, the sea ice is diminishing much faster than any of the models predicted, Meier said.
Background on the sea ice monitoring is online at nsidc.org/news/press/2007_seaiceminimum/20070810_index.html