Month: November 2012

A Reconciled Estimate of Ice-Sheet Mass Balance

Shepherd et al.: Science 30 November 2012: Vol. 338 no. 6111 pp. 1183-1189 DOI: 10.1126/science.1228102:

We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year−1 to the rate of global sea-level rise.

Aunty says Sea-level rise from polar ice melt finally quantified but then immeadiately backs off to the most definitive assessment so far, which seems more accurate. In case you can’t read the abstract, they’re saying that only E Ant is gaining mass, and that at a low rate, so overall Ant is losing, and Greenland is losing even more. Still – that adds up to 0.6 mm/yr. So it will have to grow if its to become interesting by 2100. And undoubtedly it will, but that means predicting it remains interesting, since (linear) extrapolation is obviously pointless.

Oh go on then, I’ll say a bit more. Quoting Aunty:

The lead author of the research, Prof Andrew Shepherd of Leeds University, said the study brought to an end 20 years of disagreement between different teams.

“We can now say for sure that Antarctica is losing ice and we can see how the rate of loss from Greenland is going up over the same period as well,” he added.

“Prior to now there’d been 30 to 40 different estimates of how the ice sheets are changing, and what we realised was that most people just wanted one number to tell them what the real change was.

“So we’ve brought everybody together to produce a single estimate and it turns out that estimate is two to three times more reliable than the last one.”

I’m not sure that “most people just wanted one number so we gave them what we wanted” is a good argument. Not having read the paper, I don’t know how they converted multiple numbers into one (by James’s barometer-dropping perhaps? By actually trying to work out why they differed? Either of those would make sense).

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.]

Manley: Climate and the British Scene

DSC_1880-manley-climate-and-the-british-scene_crop From the department for historical research. I happened to be in the Oxfam bookshop trying to empty our house, when I looked down and saw this in the pile of new arrivals. It hadn’t been priced but they took a fiver for it, which seems fair enough. Its a very British-meteorologist book, you can practically see him puffing on his pipe as he writes it. I am, of course, going to skip over all the nice climate and weather stuff, and look at the climate change, much to his dismay.

Manley factoid: he is buried in Coton churchyard.

You can read a few pages I’ve uploaded if you like, but you’re better off going to the convenient online copy. My copy is the fourth edition, by Collins / Fontana. It is marked as first published 1952, copyright 1952, but first published in Fontana 1962. The preface says that certain tables have been brought up to date (1961). The online one thinks it is from 1971. Manley died in 1980.

What’s the point?

To look at what he said, then, about past variations in climate. Most of the book isn’t: its about the actual climate. But on my page 279, in a table of various periods coming up towards date, we have:

About 500 B.C.

Climate again much damper with considerably cooler and more cloudy summers, less evaporation, more wind and rainfall. Rapid growth of peat over previously forested uplands especially where less well drained. Tree-line lowered by perhaps 1,000 feet. Birch increases in lowlands and in damp sites oak, alder and willow especially prominent. Summers perhaps 4o cooler than previous phase, winters still rather mild due to much wind and cloud (‘early Iron Age’).

Historic.

Possibly minor amelioration and recession in Roman times; improvement about 7th and nth century, wetter around 1100, again more disturbed after 1300. Minor fluctuations with tendency for colder winters after 1550; tendencies probably more or less similar to those shown by Fig. 64. Minor drier and wetter groups of years in S.E., but uncertainty how far these are applicable in N. and W. Prevalence of colder winters in later 17th century, and recurrence 1740 onward; groups of generally warm summers, e.g. 1772-83; and cool, 1692-1700, 1809-18. Tendency in direction of milder winters since 1850 or earlier but not uninterrupted. Appreciable increase of average temperature in spring, summer and autumn since 1930. Despite 1959, the peak may have been passed.

[I’ve correct the OCR a couple of times, but otherwise this is copied from the online text. You can’t tell from this fragment, but from surrounding text I believe that temperatures are in Fahrenheit (good gracious) and so that 4o presumably is.]

DSC_1879-manley-fig-64-crop You’ll want to see fig 64, I imagine, so here it is.

Notice that he doesn’t share our obession with temperature being of overriding interest besides which everything else pales. And that although he describes cold temperatures around what we’d now call “Little Ice Age” kind of times, he doesn’t use the phrase. Of “Medaeival Warm Period” for that matter. And his temperature graph sticks a big upwards spike in “LIA” times.

He doesn’t explain these variations, though there is speculation about solar variation, perhaps acting via changes in circulation. The greenhouse effect isn’t mentioned; CO2 is, briefly: The atmosphere which envelops us is in the main a mixture of gases ; some of these are the permanent constituents, about one-fifth oxygen and nearly four-fifths nitrogen with small quantities of other gases. Water-vapour is the principal variable constituent; carbon dioxide is a minor variable constituent of potential importance. But the “potential importance” teaser isn’t followed up, as far as I can see.

He’s also very unclear about what might have caused the ice ages. Milankovitch doesn’t get a look in: Other suggestions have been made which postulate considerable variations in the intensity of solar radiation. It has been demonstrated by Sir George Simpson that a small increase in the power of the sun would ultimately give rise to increased cloud and precipitation in highland regions towards the poles; assuming that the land was already sufficiently elevated, the resultant increased cloudiness and snowfall would gradually give rise to an ice cap. He points out the importance of the fact that a widespread cloud sheet, once formed, reflects a great deal of the radiation falling upon it. The elegance with which his theory can be extended to explain the occurrence of cooler and warmer interglacials is attractive; it was published in the Quarterly Journal of the Royal Meteorological Society for 1934, with some revision in 1957. But unfortunately, sufficient geological evidence is not forthcoming with regard to the relative coolness or warmness of the several interglacials which Simpson’s theory would require; interglacial deposits are rare, as they are generally removed by the succeeding glaciation. For this reason the elucidation of the full story of the British glaciations is tardy. Moreover full agreement has not been reached with regard to the number and extent of the several glaciations in other parts of the world.

None of which matters, really: its just an illustration of what people thought, then. And is perhaps some counter to the “Age of Gold” nonsense that some people spout.

Why a 4°C Warmer World Must be Avoided (part 2)

4oc Previously I criticised this world bank report, because of some injudicious choice of phrasing. However, various people suggested that I could consider actually reading the report and seeing what it had to say. Obviously I’m not going to do that in detail, but I can try skimming it. I wrote some stuff whinging that their use of “likely” and “could” was ill-defined, but decided that was boring, so deleted it and started again.

Oh, and yes this is yet another excuse for not writing about sea ice; but I can at least formally acknowledge losing my bet with Neven (and one of them with Crandles).

How Likely is a 4°C World?

They ask. And its a good question, well at least if you’re writing a report about a +4oC world its an essential question. So, what’s their answer?

The emission pledges made at the climate conventions in Copenhagen and Cancun, if fully met, place the world on a trajectory for a global mean warming of well over 3°C. Even if these pledges
are fully implemented there is still about a 20 percent chance of exceeding 4°C in 2100 [10]. If these pledges are not met then there is a much higher likelihood—more than 40 percent—of warming exceeding 4°C by 2100…

I’m not sure that’s a desperately useful way of looking at future CO2 trajectories, but its plausible, at least to the sort of people that probably went to C or to C and took them seriously (I did neither; that reminds me, Timmy has another excellent article about carbon tax which you should certainly read, unless you already agree with everything he says there. Perhaps …Texas becomes uninhabitable for weather reasons not cultural ones… is enough to tempt you?).

Footnote 10, which is their methodology, is interesting:

Probabilities of warming projections are based on the approach of (Meinshausen et al. 2011), which involves running a climate model ensemble of 600 realizations for each emissions scenario. In the simulations each ensemble member is driven by a different set of climate-model parameters that define the climate-system response, including parameters determining climate sensitivity, carbon cycle characteristics, and many others. Randomly drawn parameter sets that do not allow the climate model to reproduce a set of observed climate variables over the past centuries (within certain tolerable “accuracy” levels) are filtered out and not used for the projections, leaving the 600 realizations that are assumed to have adequate predictive skill.

I’ve heard of this idea, but its not something I’m used to seeing being used. I assume it produces answers not too dissimilar to the usual throw-a-stack-of-GCMs-against-the-wall kind of stuff in IPCC, and who is to say which is better. Probably they should all be looked at more as representative and scenario-generating rather than serious attempts to constrain likely future ranges. But then, I’m getting increasingly out of touch with this stuff. Ask that nice Dr Annan instead.

But anyway: what I’d take from that, summarised in a way I could agree with, is that given the CO2 scenarios we can’t rule out, it is possible but less than even-odds-likely, that we’ll exceed 4oC by 2100. Note that (their fig 20) RCP 6 is somewhat lower than A1B from the olde dayes.

They then point out that lots of CO2 leads to ocean acidification as a problem of its own, which I assume is correct (I didn’t read it, or the drought stuff, or the cyclones stuff). And so on. It becomes clear that this is mostly the std stuff, and they are drawing from the std resources that you’d hope they’d use.

So if you strip away the over-emotive language used in some parts of the report, most obviously in its foreword, you’re left with this from the executive summary:

A 4°C world would be one of unprecedented heat waves, severe drought, and major floods in many regions, with serious impacts on ecosystems and associated services. But with action, a 4°C world can be avoided and we can likely hold warming below 2°C

which seems fair enough (apart from the extraneous comma in the last sentence, of course, which isn’t fair at all).

Turn Down Heat: Why a 4°C Warmer World Must be Avoided?

4oc Says the World Bank [*]. I could see why an imminently 4 oC world would be problematic. But the problem, as Timmy rather bluntly pointed out, is the report saying it spells out what the world would be like if it warmed by 4 degrees Celsius, which is what scientists are nearly unanimously predicting by the end of the century, without serious policy changes (my bold) which is, errm, bollocks. Note that they really are talking about global average temperature here, so it isn’t possible to fix this up by saying they are talking about land, or NH land, or somesuch.

That’s from the foreword, which is presumably designed to gain attention at the expense of accuracy. The Exec summary is a bit better, reporting Even with the current mitigation commitments and pledges fully implemented, there is roughly a 20 percent likelihood of exceeding 4°C by 2100. That’s starting to become something believable. There’s rather a degree of vagueness about whose estimates and scenarios are being used at that point; we’ll need to read further to find out, into chapter 3, 21st Century Projections.

Even there things are a touch vague, but The nonmitigation IPCC Special Report on Emissions Scenarios (SRES) (Nakicenovic and Swart 2000), assessed in the IPCC AR4, gave a warming range for 2100 of 1.6–6.9°C above preindustrial temperatures. In these projections, about half the uncertainty range is due to the uncertainties in the climate system response to greenhouse gas emissions. Assuming a “best guess” climate response, the warming response was projected at 2.3–4.5°C by 2100, the remaining uncertainty being due to different assumptions about how the world population, economy, and technology will develop during the 21st century. No central, or most likely, estimate was provided of future emissions for the SRES scenarios, as it was not possible to choose one emissions pathway over another as more likely (Nakicenovic and Swart 2000). The range from the SRES scenarios, nevertheless, indicates that there are many nonmitigation scenarios that could lead to warming in excess of 4°C indicates, I think, that we’re in IPCC land: these are std climate model projections. And However, RCP6, one of the RCP mitigation scenarios that assumes only a limited degree of climate policy intervention, already projects warming exceeding 4°C by 2100 with a probability of more than 15 percent is, I think, where they are getting their 4 oC from.

So, OK, it is possible to find 4 oC from the std projections. However it isn’t possible to say what they do say, viz “warmed by 4 degrees Celsius, which is what scientists are nearly unanimously predicting by the end of the century”. Its only a possibility. Now you could say, as mt does and I largely agree, that you need to weight these less-probable-but-not-clearly-assessable probabilities carefully – but that is a different matter. As is all the response and impacts stuff in this document, which I haven’t read.

[*] Or do they? Actually This work is a product of the staff of The World Bank with external contributions. The findings, interpretations, and conclusions expressed in this work do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. So maybe not.

Update: AA makes a good point in the comments, which I should have said upfront: that focussing on 2100, as though the warming will stop then, isn’t good. The graph here makes that clear. Nonetheless it doesn’t get the Bank out of their textual hole, since they very clearly said “by the end of the century”.

Refs

* Climate Scientists Applaud Dire World Bank Report – LiveScience (that’s “Dire” as in “worring”, I think, not as in “hopeless”).

When will it start cooling? (again)

The Watties are back to plaintively whistling for cooling. This time its “Dr.” Norman Page, and just like last time there isn’t really any point wading through the details because its all self-deluding nonsense.

But what’s funny is to realise how throw-away all this is, how it lacks any coherent theory, and how they are effectively admitting that themselves. If this actually meant anything, if it fitted together, then the new post would reference the old one. Obviously. Because the old post was valuable – wasn’t it? The new post advances the state of the art the old post represents, or perhaps provides a newer interpretation. But either way, the old post is relevant – isn’t it? And yet neither the new posts author, nor any of the commentators, think that the old post is even worth mentioning.

Its almost as though this stuff is just throwaway tabloid fodder.

climatedialogue.org

Go visit; its at climatedialogue.org. And Bart is involved, so it is at least promising. On the other hand the About Page says it exists because the Dutch Parliament… asked the government ‘to also involve climate skeptics in future studies on climate change’. That’s pol-speak, therefore stupid. Any scientists with anything valuable to say, via the peer-reviewed literature or, I suppose, in other ways, is or can be already involved. However, don’t let me be too negative too soon.

The first topic up is Melting of the Arctic sea ice and that’s not a bad idea for a start. Inevitably, the discussion focusses almost immeadiately on “woz it us wot dun it?” I skimmed Walt Meier’s stuff, and Ron Lindsay, because they’re giving the std line I believe fundamentally the main process causing the decline in Arctic sea ice is increasing greenhouse gases (that’s Ron’s take, Walt’s isn’t too different). Since I agree with that, its a bit dull. The interesting bit, of course, is how Curry is going to wriggle out of agreeing, whilst not sounding too wild-eyed.

The answer of course begins with obfustication (we don’t have a great long-term record, etc; a long list of possible processes, carefully qualifying radiative forcing by claiming dominance from clouds; an “explanation” for the recent decline that carefully “attributes” most of it to mysterious “circulation changes” and so on). But eventually there’s no avoiding some kind of assessment, and Curry opts for

My assessment is that it is likely (>66% likelihood) that there is 50-50 split between natural variability and anthropogenic forcing, with +/-20% range.

So… what does this mean, if anything? There is a 66% (or more) likelihood that is 50-50 (or so) anthro/var. So the remaining 33% is filled up by, errm, what? 100% anthro? 100% var?

Marcel Crok (who I don’t think I have much time for) does perceptively home in on this asking “Now what exactly does this mean?”. Her answer seems, to me, to shift meaning, by rephrasing it as “I think it [sic] a simpler way to look at this would be to attempt to put bounds on the AGW contribution to the recent sea ice melt. I propose a range of 30-70%”. So now I think she is 100% confident that the recent melt is at least 30% anthro, and not more than 70%.

Does this matter? Weeeell yes: you’d expect Curry to have got her thoughts into order on this; after all she starts off her posting by listing 4 previous blog postings she’s done. And surely she gets quite a lot of comments on her blog; at least some of those must be signal rather than noise, and there must of been some debate, which she must have listened to, about her rather odd notions of probability. She has form, as James Annan has had cause to complain before.

For myself, I wouldn’t rule out anthro as causing 100% of the decline (this essentially means that I’m saying I don’t trust at least the GCM ensemble very much, which I don’t). Walt wimps out of offering a number; Ron is vague but goes for about 50%. How useful is this as a question? We don’t really have the tools, at the moment, to pin down the exact number, and we know that full well.

How does the discussion then fare? That, after all, is the point of this stuff. The first CAGW nutter turns up as comment 3. Nutter then keeps turning up, says that even Curry “routinely chooses topics for discussion which assume CAGW is correct”, when asked to propose a “skeptic” scientist who should have been involved suggests “Anthony Watts, Richard Courtney, Christopher Monkton…”. Then nutter #2 turns up, and I stopped counting at nutter #3 a little later.

Rob Dekker makes the first comment that really attempts to discuss the science. After that it gets better, with four or five comments actually about science. Those comments really deserve answer from the three guess bloggers, to make this actually work as a dialogue. And they’re going to have to work out how to suppress the nutters, if they don’t want to drown in noise (update: I see they’ve moved some to “Off-topic comments” – that’s a good start).

Update: well, I commented there, but my fine comment got moved into the “off topic” section with all the nutters (webcite). So, I’m not exactly impressed by their quality control. Indeed, I’m offended. Perhaps they don’t really want a dialogue with the likes of me at all?

Uupdate: I’m back, it would appear (webcite), as though I’d never been away (I think it would be more honest of them to keep the to-and-fro history of the comments available, though that may be hard).

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