Take a look at the latest charts from the National Snow and Ice Data Center. After running for several months above the refreeze trend line for 2007-2008, the 2008-2009 line is now poised to dip below last year’s.
As I have already reported, 2008 was the 2nd lowest year for summer sea-ice extent falling just short of the record set in 2007. Moreover, 2008 set a record for lowest sea ice volume. Despite the fact that 2008 was colder than 2007, the sea-ice melt rate for 2008 nearly equaled the previous year. Why did that happen? Well, in 2007 a lot of the ice that melted was multi-year ice. In 2008 after 2007’s record melt a lot of new ice formed in the fall, but it was thin being first year ice. Such ice melts more easily.
Now take a look at the amount of first year ice in 2008 compared with 2007.
The increase in first-year ice is very large, which brings us to the significance of this year’s refreeze trend line. The science-impaired denailist/delayers were getting all excited about this year’s refreeze rate, because, even though it was well below the 1979-2000 average it was above the 2007-2008 refreeze rate. Now, of course they didn’t mention what I’ve just written about first-year versus multi-year ice, but that is precisely the point.
Just as last year, much of the 2009 ice cover will be first year ice which will be easily susceptible to melting, and, now, it appears that the refreeze rate for 2008-2009 is about to go below last years rate. (For a possible reason for this, see this post: Changes Taking Place in Arctic Sea-Ice Growth and Melt Cycles)
What does this mean for next summer’s sea-ice melt? Maybe nothing, but allow me to speculate a little. If much of the sea ice come next summer is first year ice and it will be, (and a lot of the rest will be second-year ice), and if this years refreeze trend line does go below last year’s line and stays there so that we start out with a smaller ice extent, and the La Niña pattern that we’ve been having shifts to an El Niño we could easily have a new record for sea ice melt come September 2009. I should point out that the World Meteorological Organization stated in late November that it could not, at this point, make a prediction regarding El Niño-La Niña for spring 2009.
Forecast models are in general agreement that near-neutral conditions will prevail through the remainder of 2008, and that there is no substantial risk of El Niño or La Niña through the remainder of 2008 and indeed into early 2009. However, confidence in projections into early 2009 carry increased uncertainty. Expert interpretation refrains from drawing any robust conclusions at this time about the likelihood of El Niño or La Niña development during the historically favoured time of year of March-May.
So, two of my three if’s may not happen. The refreeze rate may move back up and we may not have an El Niño next year, but if we do we’re going to see a new record for summer sea-ice melt and my guess is that it will be by a big margin. Just another step to a summer-sea-ice-free Arctic, decades before when the IPCC and others said it could happen.