Now that August numbers for sea ice area and extent are available from NSIDC, let’s update the prediction of the upcoming September value.



This September we’re sure to see either the lowest or the 2nd-lowest extent value on record. This is clear from looking at daily data from JAXA (this year’s data in red):

We can even take a close-up look at the summer/fall, to see that we’ve almost passed into second place already even though these data only go up to the end of August:

If we look at the monthly averages from NSIDC we see that for August, extent was 2nd-lowest on record (and very nearly as low as 2007):

As for area (rather than extent), this August beat 2007 for lowest on record:

That’s important, because when it comes to predicting September extent, August area turns out to be a better predictor than August extent.

July’s values similarly portend a record minimum this year. For this July, both extent and area were the lowest on record:

If we model the September extent as a function of August values for both extent and area, the model predicts a September value of 4.35 million km^2, which would not break the 2007 record (but it’s close to the NSIDC record of 4.30). However, if we also use extent and area data from July, the model has better AIC value and predicts a September extent of 4.17 +/- 0.4 million km^2 — which would be a new record low:

All this would indicate that it’s likely (but only slightly more likely than not, about 5-to-3 odds) that this September will break the 2007 record.

On the other hand …

If we look at JAXA data, the August 31st value is 4.744 million km^2. This already makes it the 3rd-lowest annual minimum on record, and knocking on the door of being 2nd-lowest (a door it should cross very soon).

Even so, it we compute the changes from the present date (August 31) to the annual minimum in order to estimate how much further it might dip this year, then subtract those values from the present extent, we expect the JAXA minimum to end up somewhere between 4.21 and 4.60 million km^2. Of course, that’s the JAXA minimum not the NSIDC September value which we’re trying to predict, but those two numbers tend to be pretty darn close.

What’s the bottom line? If I had to bet (which thank goodness I don’t), I’d say the odds are just about 50-50 that this year’s NSIDC September extent will set a new record low. Of course, a lot depends on the weather! In fact, the next week or even the next few days may show a sudden turn for the better or the worse, so this 50-50 proposition may become much more lopsided within a handful or two of days.

However it finally turns out, this much is abundantly clear: the trend continues. The reason: global warming. But I’ll make another prediction: if 2011 doesn’t break the 2007 record, then some fake skeptics will refer to the continuing decline as a “recovery,” and/or find an excuse to explain away this year’s appallingly low value as a weather phenomenon in hopes of drawing attention away from the trend. Probably at WUWT.