Freedman: Arctic Sea Ice May Set Record Low
The Interior Department's decision last week to list the polar bear as a "threatened" species under the Endangered Species Act (ESA) may soon be seen as either a prescient move, or possibly even as too little too late, if scientists' ominous predictions for this summer's Arctic sea ice melt and for future seasons prove correct. A number of predictions have been issued in the past several months, all indicating that 2008 has at least a decent chance of beating out 2007 for the title of the greatest summer sea ice loss on record.
In fact, some experts have concluded that the North Pole itself may be covered by water, rather than ice, during the peak of the annual melt season at the end of the summer, and that the Northwest Passage could be ice-free for a time as well.
The recent predictions offer an unsettling picture of the astonishing rate of environmental changes that have been taking place in the far north. Sea ice loss also puts the pace of climate change policymaking into perspective, since there is a stark disparity between the rapidly melting Arctic and the slow pace of Washington policymakers.
An examination of new information about Arctic sea ice dynamics illustrates this point. According to recent analyses of Arctic sea ice, the ice that is entering the 2008 summer melt season is thinner and younger than the ice that melted like butter on a frying pan last summer. With sea ice, the opposite of the Hollywood ideal of young and thin is desirable, since new and thin ice melts more rapidly than thicker, older ice.
Late last month, University of Colorado at Boulder researchers found that only two percent of Arctic sea ice was older than normal (defined in that study as the period between 1982 to 2007), while 63 percent was younger than average. Consistent with this assessment, National Snow and Ice Data Center (NSIDC) researchers reported in April that first-year ice covered a whopping 72 percent of the Arctic Basin, including the area around the North Pole. The NSIDC noted that Arctic sea ice had recovered in terms of geographic extent from last summer's record melt, but that last summer's decline was so large that there was precious little older ice left over to build up during the winter.
Recent atmospheric conditions have also contributed to the Arctic sea ice's young and thin problem, including a positive phase of the Arctic Oscillation in which pressure patterns steer storms farther north, bringing stronger surface westerly winds in the North Atlantic and warmer and wetter than normal conditions to the Arctic and northern Europe. Such winds helped to flush older ice out of the region this winter, leaving a large expanse of younger and thinner ice to enter the 2008 melt season. Last summer, unusually sunny weather during portions of the summer season contributed to the record melt.
Although it remains to be seen whether atmospheric and ocean conditions will combine to create another record sea ice melt this year, most predictions indicate that there is a high likelihood that this year's melt season will at least result in well below average Arctic sea ice extent (average here refers to the 1979-2000 period).
"Even if more first-year ice survives than normal, the September minimum extent this year will likely be extremely low," the NSIDC stated on April 7.
The University of Colorado's sea ice forecast indicated that there is a three-in-five chance that the 2007 record low for Arctic sea ice extent will be exceeded this year due to the combination of warming temperatures and the preponderance of younger, thinner ice. And the NSIDC has declared that it is "quite possible" that the North Pole will be ice free during this melt season.
According to a study published in February in Geophysical Research Letters, computer model predictions show a 50 percent chance that the Northern Sea Route and the Northwest Passage will be "nearly ice free" in September of 2008. The study indicated that sea ice loss this year is likely to progress more slowly than last year, and reach a low but not necessarily record-breaking minimum.
The NSIDC's May 5 sea ice news and analysis stated that only 30 percent of first-year ice typically survives the summer melt season, compared to a 75 percent survival rate for older ice. NSIDC scientists compared survival rates from past years with the 2008 April sea ice coverage and determined that in order to avoid breaking last year's record, more than 50 percent of this year's first-year ice would need to make it through the melt season. To put this into further perspective, only 13 percent of first-year ice survived last year's record melt.
Last year, sea ice melted to a record low that far exceeded 2005's record melt. In September of 2007 (September marks the end of the summer melt season), the sea ice cover was 23 percent below the 2005 level and 39 percent below the long-term average from 1979 to 2000.
The melt was so rapid last year that, according to Sheldon Drobot of the University of Colorado, during a two-week period the area of sea ice lost was equivalent to losing the area of Kansas every day.
Scientists blame human emissions of greenhouse gases for much of the Arctic sea ice decline, but natural factors are also at work in the region, such as variations in ocean currents and atmospheric cycles including the Arctic Oscillation. The interactions between natural cycles and human influences is a key research area during the current International Polar Year.
Whether or not sea ice cover hits a new record low this year, however, it's likely that the overall decline in sea ice will have negative repercussions on polar bears and other ice-dependent species. This is, of course, the reason for the Interior Department's begrudging polar bear listing last week. The Interior Department's press release stated as much when it said, "loss of sea ice threatens and will likely continue to threaten polar bear habitat. This loss of habitat puts polar bears at risk of becoming endangered in the foreseeable future, the standard established by the ESA for designating a threatened species."
However, assuming a strong relationship exists between sea ice loss and species decline, after looking at the latest predictions and the recent Arctic sea ice data, I wonder how soon it will be before polar bears are pushed into the endangered category. Hopefully policymakers will catch up to the scientists, who are themselves struggling to stay abreast of the rapidly changing environment. According to NSIDC, one sea ice expert, Ron Lindsay of the University of Washington, has cautioned that "sea ice conditions are now changing so rapidly that predictions based on relationships developed from the past 50 years of data may no longer apply." In other words, we're now in uncharted territory.
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