Time for another look at sea ice. Here is the familiar IARC-JAXA plot:
And we see: well, it is looking low, and has been consistently all winter. Not record-breakingly, like it was last December, but even so. Interesting.
This year, I’m not planning to run a book, unless anyone offers to make a worthwhile bet. I’ll put up my “prediction”, which is the same as ever: the mean prediction is for the trend amount, i.e. the same as last year minus a little bit (5.235, as I recall), and the “bet range” is that plus or minus interannual variation, which as I recall is around 0.5 units. If you happen to believe that this year’s ice will be stonkingly low (or, indeed, high), then perhaps we have something to bet about.
C points out that Intrade is offering prices on 2011 being greater than 2007:
and hopefully that chart will make sense for a while. I think I should probably be buying at that price (42.5) since I think 2011 will be greater than 2007. And so, I did.
But the other seaice-y thing I was supposed to do was go back and rip to shreds Gareth’s prediction of an ice-free Arctic by 2016 (I know, he didn’t quite say that, but never mind, I’m eggagerating for effect). Tell yer what, I’ll quote him:
if the relationship between ice volume and extent evident in the NSIDC and PIOMAS data over the last 21 years continues in the near future, then the Arctic will be effectively ice-free in late summer sometime between 2015 and 2020
Now there area couple of problems with what Gareth has done. The first is (on taking a second look) rather striking: he hasn’t done the projection properly. He has taken the trend-line over the last, say, decade; but he has anchored that trend on the last value. Which is lower than the trend line. So he hasn’t projected the trend line itself forward, though he has (I assume) used the right slope. For volume, that makes a difference of about 2 units (by eye) which is worth about 5 years (on the 2001-2020 version). Similarly, the thickness will be strongly affected. However, I disagree by more than that.
Fundamentally, I think his projection of volume and thickness trends forwards, and using them to derive extent, is non-physical. Or perhaps, not using the best quantities. I think the extent (or, equivalently, the area) is more fundamental.
This is driven by my view of the sea ice as part of the energy balance of the Arctic. Ice free ocean (in winter) is going to freeze and make metre-thick ice. And if it survives the summer, it will thicken over time, until advected away and melted, or melted in place. And there is a certain “natural” area of winter ice. So unless something unusual and exciting happens during the spring and summer (as it did in 2007) the ice will follow its usual patterns. I’m not explaining myself very well, I can tell. Let me try just a little bit more: in winter, there is “excess cold” available: the ice freezes up, till it is ~1m thick, and then it doesn’t grow much more, because of the insulating effect (waves hands for effect). But in summer, melt is ~linear on the warmth available. So there is a sort of stabilising effect.
Of course, I may be wrong; this isn’t my field any more. And its not as if I’m betting the farm on this. But it is what I’m basing my “predictions” on, and why I still expect there to be summer ice in 2050.
I still need to fold this pic I drew last year:
into my analysis. That suggests that I am over predicting ice by ~0.4 units.
ps: via the Baron, I see that Curry is still pulling numbers out of her hat instead of doing science. But that is blog science for you: you can just make stuff up and no-one cares. When did Curry change from being a serious scientist into a comic turn?
pps: I’m finding Early Warning interesting reading nowadays. Lots of graphical analysis of oil prices.