The animation which Dr. Meier from NSIDC posted on WUWT is very helpful.
It shows how old NSIDC believes the ice is, for each week from mid-September 2009 to mid-September 2010. So theoretically we should be able to do an apples for apples comparison between the start and end dates. But there is a major problem …
Some years they advance the ice age on week 37, and other years they do it the next week. In 2009 they had already thrown a birthday party for the ice by Sept 15, but in 2010 they hadn’t. So it appears that a lot of older ice has been lost in 2010, which is not the case.
Week 37 2009 Week 37 2010
The images below give the 2010 ice it’s proper birthday party, so that we can do a real apples for apples comparison. It is not clear to me why NSIDC did not shift the start/end dates by a week so that a proper comparison could be made.
Week 37 2009 Week 37 2010
Now that looks better, doesn’t it? Lets do the math and see how much multi-year ice (MYI) there actually is.
There is more three and (a lot more) four year old ice now than in 2009, and less five year old ice. This is what we would expect, because all the first year ice melted in 2007. Because of the loss in 2007-2008, it was mathematically impossible to have a recovery of five year old ice until 2011-2012.
Also, the bulk of the three year old ice is located further west than last year, where it is more likely to survive – so there should be less loss of MYI over the winter.
Conclusions :
- The MYI is recovering. The amount of four year old ice has more than tripled since last year.
- NSIDC should have either shifted the start/end dates of the animation by one week in either direction, or they should have aged the 2010 ice on week 37. The animation they provided shows a steady decline of MYI from frame one to frame fifty-three. One more frame was needed to be a useful representation of the year-over-year change in the ice.