RealClimate has an interesting post on arctic sea ice from Dirk Notz at the Max Planck Institute, which discusses (among other things) the obsession with the summer minimum extent. He adroitly points out several interesting points. One is that weather conditions strongly affect the summer minimum, so it’s really too early to know whether this summer’s minimum will be a record-breaker or just ho-hum. Another is that the decline in arctic sea ice thickness is where the real story lies, but for the moment thickness is not nearly so well-observed as extent so it’s extent that captures the most attention.
In spite of the uncertainties (or perhaps because of them), it’s still fun to predict what the future will bring. Everybody seems to want to get a piece of the action; the June outlook from SEARCH offers predictions from a number of researchers:
We can’t let professional arctic researchers have all the fun! After all, Shemp has his forecast for the summer minimum in arctic sea ice extent. Here’s mine.
NSIDC has posted their monthly figures through June, and of course we have access to daily data (for the northern hemisphere at least) from JAXA, although those data don’t begin until 2002. In my opinion, it’s important to incorporate the long-term trend, which just isn’t as well defined by the briefer JAXA data. I also note that the September average from NSIDC is a pretty good match to the recent summer minima from JAXA:
There are notable differences, but those are mainly in winter. I think (but I’m not sure, perhaps some knowledgeable reader can enlighten) that the JAXA group doesn’t count certain southern areas that only freeze over in winter, so there’s a notable difference in winter maxima but little in summer minima. In any case, the NSIDC September average is a pretty good proxy for the JAXA summer minimum — and it goes back over 30 years, not just 8.
What has the September average done for the last three decades? This:
The decline is obvious. What may not be obvious (without the regression line) but is still clear, is that the decline has accelerated. That’s why I’ve fit a quadratic trend line. So here’s a simple projection: I’ve extrapolated the trend line to this year. Which gives a predicted September extent of 4.78 million km^2 (plotted as the red dot on the graph). I’ll call that my forecast for the summer minimum.
We can also use the scatter in the residuals from the trend-line fit to estimate the uncertainty in that prediction. Make that 4.78 +/- 0.95 million km^2 (plotted as the “error bar” on the red dot in the graph).
That puts my forecast for the summer minimum extent at somewhere between 3.83 and 5.73 million km^2. My low end is lower than any of the pros prognosticated (except for Wilson, that Maverick!), but my high end is about equal to the most conservative professional opinions.
If the range I’ve outlined seems kinda uncertain, well, that’s the way forecasts are. As Dirk Notz emphasizes in his RC article, this summer’s weather will have a lot to do with the minimum, and that’s something we really can’t predict. The uncertainty is in the system.
Nonetheless, I expect this summer’s extent to be less than last year’s. I’ll give that an 89% chance of happening. As for who’s prediction will be closest to reality — time will tell.