March is the time of year when the ice in the Arctic reaches its yearly maximum areal extent. The Vernal Equinox is coming up in a couple of weeks, which means that the Northern Hemisphere is going to start receiving more sunlight than not every day. The National Snow and Ice Data Center released a news update this morning on this subject. Here are a few items worthy of examination.
Ice extent averaged for February 2009 is the fourth-lowest February in the satellite record. February 2005 had the lowest ice extent for the month; February 2006 was the second lowest; and February 2007 is in third place. Including 2009, the downward linear trend in February ice extent over the satellite record stands at –2.8% per decade.
The news release has a times series graph demonstrating this decline. The site also has an ice extent vs. date graph in which it compares winter 2008-09 extent to the climatological average (1979-2000) and to the 2006-07 data. 2006-07 is used because the record minimum extent occurred in the fall of 2007. Comparing today’s conditions to the worst ever is a good idea, I think. I’ve read murmurings from the climate change denialists that things are fine since today’s extent isn’t as bad as the worst case. That’s like saying today’s economy is fine since it’s not quite as bad as the 1st Republican Great Depression. It’s a ridiculous statement to make. The extent of Arctic ice today is nearly 1,000,000 sq. km. below normal (dynamic link – only good for a few days).
The long-term trend is clear and it isn’t good. The Arctic needs but the right kind of summer weather conditions in order for even more ice to melt this year. And that’s what’s hidden in the areal extent data: it says nothing about ice volume, which is dangerously low. The amount of multi-year ice decreased to very low levels last summer/fall. That makes this year’s ice pack all the easier to melt.
Related to the news release is the state of the Antarctic ice sheet. It appears to have reached this year’s minimum areal extent of about 2,000,000 sq. km (dynamic link – only good for a few days). That’s the climatological norm for this time of year, which is quite a different story than what denialists would have the public believe. According to them, Antarctic glaciers and ice are increasing. That is devoid of the requisite detail to describe the actual reality. Compared to this same date last year, there is ~600,000 sq. km. less ice today. I won’t speculate on whether this is indicative of any kind of trend. It’s certainly at the long-term average. My worry last fall was the maximum areal extent reached a near-record low, which was a clear break in a recent trend. How the ice sheet fares this austral winter remains to be seen, of course.
Recent news of melt rates increasing at both poles is very disconcerting. Global ice conditions remain in less than healthy shape, as this graph demonstrates. Last spring saw the only above-average areal ice extent since 2003. Every other data point since then has been at or well below average.