Posted by There has been lots of discussion of this year’s arctic sea ice extent. Last year was a shocking 23% lower record breaker. That’s 23% lower than the previous record, for which one had to go all the way back to….2005! That’s not 23% below the 1979-2001 average, but 23% below the lowest previous measurement! 2005, aside from being the previous record, was also remarkable for being the fourth consecutive year that fell below the trend line. (With a steady decline in noisy data one would expect equal probablities of data points falling above the trend line as below.)
Here is a graph made at that time (2005). 2007′s record breaking minmum falls well off that chart, where 4 would have been on the x-axis if it had gone that low:
So, as the discussions discuss, here comes 2008, hot on 2007′s smokey trail…
Image from the NSIDC
So close! But we are down to the last two or three weeks of melting now, I’d say 2007 will squeak by.
William Connolley long ago took the boringly scientific position that it was pretty unlikely that such a dramatic record as 2007′s would be broken anytime soon, much less the very next year and has made a game of betting on it. I dare say it is a much closer call than he ever expected!
But like certain other horse races, the outcome is pretty irrelevant to the long term and substantive issues**. We do not need a new record this very year to still gasp at the rapidity of ice loss, something that not even those eco-alarmist-nazis at Greenpeace were moaning about in 2001. The ice is melting. Fast. The pretty pictures paint a not so pretty picture of a rapidly changing planet. The loss of a summer arctic ice cap also heralds the arrival of a new and potentially dramatic feedback in the form of lowering earth’s albedo. Darker sea water will absorb alot of solar radiation that white ice would have shot straight back into space. Not good news for the local permafrost.
So what was the point of this post again…oh yeah “The other arctic sea ice loss”, that’s what I called it. All of the above graphing and betting is about ice extent, that is to say it is about the area of ocean surface that is at least 15% covered by ice. But there are different kinds of ice, specifically there is new ice and multi-year ice. The graphic below is a pretty kewl illustration of what is happening to multi-year ice. I know you looked at it already, but now I will explain it a bit.
This is a composite of week by week ice thickness maps from 1981 to 2007, you can see the week count and year count in the bottom left of the image. Watch the whole thing to see the exent to which the ice is becoming younger. Five+ year ice (red) is just a shadow of what it was in the 1980′s by 2007.
Old ice is thicker, it has had multiple seasons to grow. First year ice is thinner and more vulnerable to melting. In fact, on average the sea ice there has thinned by half as of 2007. That’s thinned by half since 2001, not 1981! In 2001, ice on average was about 4 metres thick, it was down to 2 metres in 2008.
Now, I don’t know about no book lernin’ and no compooter models, but I do know about snow melting on the front lawn and ice unfreezing on the local pond-slash-skating rink, and this vast body of knowledge tells me that, new record in 2008 or not, it won’t be long now till the record low extent is 0.
That will be a record that may well go back to the Eemian, though it is hard to know for sure. But regardless, we most certainly do live in interesting times.
** talk to me later if Obama wins and does even one of the following: meaningfully reduce the military budget, establish universal health care, withdraw from Iraq, balance the budget, abolish Guantanamo and other “black sites”, take nuclear warfare “off the table”, restore FISA law.
September 3, 2008
September 3, 2008
September 3, 2008
September 3, 2008
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September 10, 2008
