Note, all NSIDC maps below have been modified with new colour schemes to make them easier to understand.

I did some more analysis of the NSIDC maps. The graph above shows the progression of ice over the past year. The first three columns are measured directly from NSIDC maps, and the last column I took the liberty of advancing all the ages of the ice by one year for week 38. Note that there is more three and four year old ice than a year ago, and less five year old ice.

Note that much of the three year old ice melted during the last winter – before week 20, 2010. The map below from week 37, 2009 shows why it occurred. At the end of summer 2009, much of the three year old ice was doomed – because it was too close to the North Atlantic.

During the winter of 2009-2010 a lot of three year old ice blew out into the North Atlantic and melted. You can see the loss clearly in the week 20, 2010 map below.

By week 37, a lot more three year old ice had melted, leaving very little.

But two year old ice was abundant, and when freeze started in week 38, the two year old ice became three years old. As you can see below, there is more three year old ice now than there was a year ago. And more importantly, the bulk of the three year old ice is located much further away from the North Atlantic. So it is quite likely that more multiyear ice will  survive the winter.

Now, let’s compare vs 1996. The graph below shows that there was a lot more four and five year old ice in 1996, but only half as much three year old ice.

The 1996 map is shown below.

Conclusions :

• Spring 2011 should see a lot more multiyear ice than Spring 2010, and a lot more three year old ice than spring 1997.
• The ice is increasing from the 2008 low.
• PIOMAS is again shown to be off base with their claims that the ice is the thinnest on record. At the end of July, their forecast minimum extent was “3.7 +/- 0.3 million square kilometers” which was 25% too low.
• With the La Niña, we should see ongoing growth of multiyear ice through next year, at least.

Of course, strong winds could change all this.

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Below is the PIOMAS 2010 forecast minimum of 3.7 million km²

Recap: Our method uses estimates of ice thickness from the PIOMAS coupled ice-ocean model as predictors for a statistical forecast of the Sea Ice Index mean ice extent in September.  Fields of ice thickness (H), ice concentration (IC), area with less than 0.40 m thick ice (G0.4m), and area with less than 1.00 m thick ice (G1.0m) are the predictors considered in this forecast.  The method is described in Lindsay et al (2008)