This is the headline on a press release from the National Snow and Ice Data Center (NSIDC) at the University of Colorado at Boulder. They are one of the goto sources for data about sea ice, either arctic or antarctic.
The final extent of arctic sea ice melting this year, as in any other single year, is a product of (large) local weather effects superimposed on (smaller) climate trends. That makes the final minimum extent very hard to predict, which has made it a bit of a horse race for the various scientific agencies that try to understand and model sea ice dynamics.
Not so hard to predict is what the denial-o-sphere’s reaction will be if the current track continues and the final melt comes in lower than last year. If you recall, last year was the second lowest extent on record and somehow the usual suspects managed to see this as sea ice recovering. This year, if last year’s “trend reversal” is re-reversed it will be their silence that will be deafening, not their hysterics.
The year on year change is not significant if you are interested in climatic changes. What is significant is the trend derived from an examination of the entire satellite record available:
From the press release:
During the first half of July, Arctic sea ice extent declined more quickly than in 2008, but not as fast as in 2007. As in recent years, melt onset was earlier than the 1979 to 2000 average. International sea ice researchers expect another low September minimum ice extent, but they do not yet know if it will fall below the 2007 record.
It is worth remembering that this is about ice extent (the area covered at least 15% by ice). If you are interested in the total amount of ice, you need to look at its thickness as well. NASA’s Jet Propulsion Labratory had a news release a couple of weeks ago that shed some more light on this other aspect, and the findings there are similarily dramatic.
From that article:
Arctic sea ice thinned dramatically between the winters of 2004 and 2008, with thin seasonal ice replacing thick older ice as the dominant type for the first time on record. The new results, based on data from a NASA Earth-orbiting spacecraft, provide further evidence for the rapid, ongoing transformation of the Arctic’s ice cover.
Unlike the ups and downs of extent, or temperatures, the average age of the ice is directly dependent on last year’s average age (and the years before that). If last year, nothing was older than first year ice, then this year, nothing could be older that second year ice. So looking at a point to point difference, like 2004 to 2008, while not the whole picture, is not the same meaningless exercise it is when looking at extent.
Putting extent decline together with thickness decline it is not unlikely that 2008 was in fact a record low for arctic sea ice volume.
It will be interesting to watch how this year continues to progress. Regardless of the final numbers, there is no evidence of anything but dramatic decline.