Arctic sea ice still on track for extreme melt

Arctic sea ice extent has declined through the month of May as summer approaches. Daily ice extents in May continued to be below the long-term average and approached the low levels seen at this time last year. As discussed in our last posting, the spring ice cover is thin. One sign of thin and fairly weak ice is the formation of several polynyas in the ice pack.

No surprise that a recent survey of leading experts with the international Arctic science community found they expect a "continuation of the recent trend of sea ice loss" this summer. How exactly does this year's sea ice extent compare with last year and with the 1979-2000 average? NSIDC has a great figure (click to enlarge):

Although ice extent is slightly greater than this time last year, the average decline rate through the month of May was 8 thousand square kilometers per day (3 thousand square miles per day) faster than last May. Ice extent as the month closed approached last May's value.

OK, so the ice area is shrinking fast. What about thickness -- an equally important determinant of how fast the ice will disappear?

Multi-year ice continues to be low

The relative lack of thick, resilient multi-year ice in the Arctic discussed in earlier postings finds further support in the latest analysis from the United States National Ice Center (NIC). NIC uses a variety of satellite imagery, expert analysis, and other information to provide information on the amount and quality of sea ice for ships operating in the Arctic. NIC scientist Todd Arbetter suggests that much of the first-year ice is likely to melt by the end of summer, saying that despite the total ice extent appearing normal, the relative amount of multi-year ice going into this summer is very low when compared to climatological averages. NIC has found that the relative fraction of multi-year ice in the central Arctic has plummeted since the mid-1990s, creating an Arctic prone to increased melt in summer. Arbetter said, "This may be a primary reason for record summertime minimums in recent years."

How hot is it in the Arctic Ocean?

Average Arctic Ocean surface air temperatures in May were generally higher than normal. While anomalies were modest (+1 to 3 degrees Celsius, +2 to 5 degrees Fahrenheit) over most of the region, temperatures over the Baffin Bay region were as much as 6 degrees C (11 degrees F) above normal. The atmospheric circulation in May was highly variable. The first half of the month saw strong winds blowing from east to west over the southern Beaufort Sea. This wind pattern probably contributed to polynya formation near Banks Island and along the northwestern coast of Alaska.

The Study of Environmental Arctic Change (SEARCH) -- (Note to self: Next time a good acronym is needed, talk to some Arctic scientists) -- prepared its May Sea Ice Outlook report for the September 2008 sea ice extent "based on a synthesis of 19 individual outlooks from the international arctic science community." They found:

Of the individual responses that included quantitative outlooks, three (3) suggest a return toward the long-term trend of summer sea ice loss; six (6) anticipate the 2008 extent to be close to the 2007 record minimum; five (5) respondents suggest additional ice loss compared to the 2007 minimum. None suggested a return to the historical average (mean 1979-2000 September values) of 7.0 million square kilometers.

I think it's going to get harder and harder to find people to take my bet.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.