Sea ice: oh no, not again

ohnonotagain Yay, more nonsense about sea ice: the traditional “US Navy predicts summer ice free Arctic by 201x”, where this time x=6. Does anyone actually believe this rubbish? If so, I have money just sitting around, bored, twiddling its little green fingers and waiting to take your bet. If “summer ice free” means “oh yeah, not actually ice free, but less than 1 million square km” then please form an orderly line. Even odds, let’s say £1k. Who’s first up?

Do I see Nafeez Ahmed there? Or Wieslaw Maslowski? No? How odd.

Found by the lost [*]:

* Ed Hawkins ‏@ed_hawkins: Brave prediction by Maslowski for ice-free Arctic in 2016 (+/-3) | http://www.theguardian.com/environment/earth-insight/2013/dec/09/us-navy-arctic-sea-ice-2016-melt…
* Gavin Schmidt ‏@ClimateOfGavin: @ed_hawkins do you mean ‘brave’ as in unphysical, unpublished and even at the time demonstrably unlikely?

[*] You can have a point if you can find the source for that. Hint: google won’t help you.

Refs

* When will the Summer Arctic be Nearly Sea Ice Free?
* Sea ice betting report for 2012. Yes, I know I haven’t written 2013 yet, but it was dull.
*The Future of Arctic Sea Ice Annual Review of Earth and Planetary Sciences, Vol. 40: 625-654 (Volume publication date May 2012), First published online as a Review in Advance on March 8, 2012; DOI: 10.1146/annurev-earth-042711-105345, Wieslaw Maslowski,1 Jaclyn Clement Kinney Matthew Higgins and Andrew Roberts

This year’s sea ice considered unexciting

Well, you may call me a wild-eyed jumper-in-too-early but I’m going to call this year’s sea ice as “unexciting”.

Sea_Ice_Extent_prev_L-2013-08-12

There’s maybe a month left, but there’s no way its going to fall off the scale in that time [*]. Indeed, its looking pretty middle of the road: about the same as 2010 or 2008. Its important to realise, of course, that this isn’t desperately surprising, unless you’re a “death spiraller”. If you’re an “IPCC is roughly right”-er then that level of decline is quite bad enough to fit in with all the std type projections. If you are a death spiraller, then you’re a looney, but I’ve said that already I think. FWIW, PIOMAS is also showing an uptick for 2013.

[*] If you disagree with this, please be prepared to put up money to support your view in a bet. Otherwise I’ll just laugh at you.

Refs

* 2012/06 – “How’s my seaiceing?”
* 2013/03 – “When will the Summer Arctic be Nearly Sea Ice Free?” and Girding my loins: sea ice
* 2012/11 – “Sea ice betting report”

How’s my seaiceing?

Its well past time to look at the sea ice extent. I don’t have much to say, so here is a picture:

Sea_Ice_Extent_prev_L-2013-06-16

We’re currently well above the minimum – indeed, we’re pushing the maximum of the AMSR era. That’s not as meaningful as it might be, because 2012 was quite well up until only a few weeks back, so this could all change. But PIOMASS, too, is showing a slight recovery from last year instead of monotonic decline. This should all be no great surprise – we don’t expect monotonic decline.

As usual, if you actually care about seaice you’re probably better off with Neven.

Refs

* Girding my loins: sea ice

When will the Summer Arctic be Nearly Sea Ice Free?

Its hardly an original question. And the answer (we don’t know) isn’t original either. In case you were wondering, this is Overland and Wang, GRL 2013, doi: 10.1002/grl.50316 (PDF courtesy of V). Different but not entirely different to A sea ice free summer Arctic within 30 years?, also in GRL; or even A sea ice free summer Arctic within 30 years-an update from CMIP5 models by Wang and Overland.

overland_and_wang

W+O discuss three methods for predicting future Arctic sea ice: extrapolation, wild guesswork, and cherrypicking your favourite model (of course they don’t use those names, they’ve made up some fancier ones, but it comes to the same thing).

Extrapolation is to be done from ice volume, not ice extent. No expense is spared to fully justify this important choice: Their main points are that sea ice volume is decreasing at a rate that is
faster than sea ice extent, and that volume is a better variable than extent to use for sea ice loss
. Well, you can’t argue with that, so I won’t try to.

Wild guesswork is the idea that ice loss occurs primarily through big loss years like 2007 and 2012, so we sort-of think of a trend, and then guess that things like 2007 or 2012 might happen, errm, sometimes.

Cherrypicking your favourite model is when you look at the sea ice observations (oddly, at this point you silently switch back to extent from volume, but since you do this silently you don’t have to explain why) plotted on top of spaghetti diagrams from CMIP and realise that you can make nothing of them. So perhaps you should throw the slower ones away.

These three different methods produce completely different answers, and so you end up concluding that you know nothing.

How might we do things better? Weeeeeellll, I’m not in the game anymore, so I can have fun. The O+W approach reminds me of Lord Dorwin, the aristocrat in Foundation whose idea of research is only to re-read the works of others. I’ve always thought (though I may not have said it very loudly, so please don’t challenge me to find me saying it somewhere) that plotting all the CMIP models is silly: some of them aren’t very good (I have a paper sort-of saying this: An Antarctic assessment of IPCC AR4 coupled models). Fig 3, reproduced above, needs to have the goo-n-dribble models removed (ah yes, cherrypicking: but no, it needs to be done on some objective grounds; see my paper). The most obvious thing about fig 3 isn’t that the obs disagree with the models, but that the spread in the models is enormous. But even with the junk removed I fear you’d find the obs retreat faster than the models; and I’m beginning to wear thin the idea that this is just a few years anomaly. So, really, we need better models and a better understanding of what is going wrong with the current models. That won’t come from spaghetti graphs or equation-free papers, though.

Girding my loins: sea ice

This is not the sea ice post you were looking for. However, it is a placeholder for putting comments, including linking to previous comments.

If I’m feeling energetic I may even make the linkages myself.

The pic shows seaice at “normal” ish; but that means little, as 2012 was also “normal” at this time of year. PIOMASS might be more interesting (thanks CR) but a month of more will make that clearer.

Early update: Oh well, since its there, Open Mind’s Arctic Sea Ice Loss, part 1 is worth a look, esp. figs 2 and then fig 6 (though I don’t think the quadratic fit is meaningful. Unless you can bring yourself to believe that the implied long-term-trend was an increase in the early 80’s).

Sea ice betting report

And not before time, you might say. Sea ice this year reached a new record minimum in the Arctic (though not in the Antarctic, which begins to look wind-driven. And before you think the two trends might be opposite-and-nearly equal, look at Tamino’s convenient analysis which I can never find). Which means I lost some of my bets. Now, what exactly was I betting on?

Crandles helpfully points me at Betting on sea ice: $10,000 although the $10k doesn’t fall due until 2016. But in the comments (the one from 2011/07/04, since perma-linking here remains invisible to all but me) we agreed:

we are betting £x that either 2011, 2012 or 2013 will beat the minimum extent record of 2007, based on daily IJIS SIE numbers (which makes it more fun), but the record has to be confirmed by the monthly NSIDC extent number.

where x=100. Neven had the same bet (recorded in Sea ice, part 2, but for E50. In defence of my own tattered reputation I’ll point out that I said at the time So to re-visit some earlier stuff: I said the chance of something beating 2007 and setting a new record low within the next 3 years (including 2011) seems quite good. So I’m not betting on that in response to Neven’s offer. But if I switch to the not-so-safe green line I think that just about fits the error bounds and only took it on for the thrills. But now I’ve lost so N and C need to email me their bank account details or some other such method of xfer (paypal would be convenient for me).

And what of the future? Who knows. Closer inspection of this post will reveal traces of me intending to talk about the actual ice, but I think I’ll postpone that for a while.

[Update: per agreement in the comments (see! I can do permalinks), Neven and I are converting our bet to double-or quits: “either 2013, 2014 or 2015 will beat the minimum extent record of 2012, based on daily IJIS SIE numbers (which makes it more fun), but the record has to be confirmed by the monthly NSIDC extent number” for E100.]

Wind-driven trends in Antarctic sea-ice drift

holland-sea-ice There’s a nice paper out by Holland and Kwok, attributing much of the somewhat-hard-to-understand change in Antarctic sea ice to changes in wind forcing. The growth in Antarctic sea ice, although much smaller than the decrease in the Arctic, is still a bit embarassing; it would be much tidier if it were decreasing. The abstract says:

The sea-ice cover around Antarctica has experienced a slight expansion in area over the past decades [1,2]. This small overall increase is the sum of much larger opposing trends in different sectors that have been proposed to result from changes in atmospheric temperature or wind stress [3–5], precipitation [6,7], ocean temperature [8], and atmosphere or ocean feedbacks [9,10]. However, climate models have failed to reproduce the overall increase in sea ice [11]. Here we present a data set of satellitetracked sea ice motion for the period of 1992–2010 that reveals large and statistically significant trends in Antarctic ice drift, which, in most sectors, can be linked to local winds. We quantify dynamic and thermodynamic processes in the internal ice pack and show that wind driven changes in ice advection are the dominant driver of ice concentration trends around much of West Antarctica, whereas wind driven thermodynamic changes dominate elsewhere. The ice-drift trends also imply large changes in the surface stress that drives the Antarctic ocean gyres, and in the fluxes of heat and salt responsible for the production of Antarctic bottom and intermediate waters.

The pic I’ve nicked is Autumn (April–June) 1992–2010 ice motion and concentration trends and their relation to wind forcing. Wind-driven changes in ice motion are clearly linked to changes in ice concentration. Ice-motion trend vectors overlaid on ice-concentration trends.

So the theory is that sea ice on the edge of the pack (well, in those areas where the wind forcing is southerly) is there because its been advected north (it can’t form there thermodynamically, and is indeed melting there). And so if you increase the southerlies, you get more ice; because further south its cold enough to produce as much ice as you like, as long as you can export it. Of course all of this (assuming for the moment they are correct) just pushes the question one step further back, because they leave the changes in wind forcing unexplained. It may also help with the why-oh-why don’t GCMs produce the observed Antarctic response: because it isn’t the rather simpler to get right thermodynamics. Of course that’s probably part of why they don’t do so well in the northern hemisphere, too.

I used to share an office with Paul, BTW.

There’s also a Grauniad article. Lets take a look, and see how they do, shall we?

The mystery of the expansion of sea ice around Antarctica, at the same time as global warming is melting swaths of Arctic sea ice, has been solved using data from US military satellites.

A poor start. As I said, it hasn’t been solved, just pushed back one step to winds. And the “US military satellites” is a bit woo: they are just the satellite-derived sea-ice motion vectors, from DMSP I think.

Paul Holland at the British Antarctic Survey. “Our study of direct satellite observations shows the complexity of climate change. The Arctic is losing sea ice five times faster than the Antarctic is gaining it, so, on average, the Earth is losing sea ice very quickly. There is no inconsistency between our results and global warming.”

Accurate, and probably a good idea before the fools get overexcited. “In some areas, such as the Bellingshausen Sea, the sea ice is being lost as fast as in the Arctic,” is a useful reminder that the Antarctic trends are very regional (again, consistent with dynamics rather than thermodynamics). Overall, by newspaper-reporting-climate standards pretty good.

How about comparing the Graun to the Torygraph? Headline: Antarctic sea ice is increasing, byline The amount of ice in the Arctic may be at a record low but Antarctic sea ice is increasing, according to a new study. First two sentences rctic summer sea ice reached a minimum 3.41 million sq km this year, around 50 per cent lower than the 1979-200 average. However a study by the British Antarctic Survey (BAS) and NASA found sea ice in the Anatarctic has been increasing over the same period. Yes, they really are doing their best to mislead you. The next few sentences actually tell you something about the paper. Um, and that’s about it. A fail, I’d say.

[Update: I should have pointed out that there is a pile of existing literature about how ozone depletion has affected the surface circulation. Thanks to Eli for reminding me; I think stuff like http://www.sciencemag.org/content/302/5643/273.short is relevant; see comments -W]

Refs

* Nature Geoscience (2012) doi:10.1038/ngeo1627
* BAS press release