September 27, 2013, by Warren Pearce
Just one number: has the IPCC changed its supply of evidence?
As I have researched online climate scepticism over the last year, its become clear that climate sensitivity has been one of the biggest topics for discussion. This is perhaps one of the easier parts of climate science to understand. Put simply, sensitivity measures the amount by which the Earth’s temperature increases when atmospheric carbon dioxide doubles (more detail here). This is a key question for climate sceptics, and explains how those who accept the existence of the greenhouse effect (most of them) can still be unconvinced about the severity of future climate change. To use a simple analogy, one could imagine sitting on a trolley going down a slope. With a high climate sensitivity the slope is very steep and we roll down very quickly, with low sensitivity we roll much more slowly. All agree hat the trolley is rolling, but the speed of the rolling is likely to affect how quickly we try and put the brakes on.
Today, the Intergovernmental Panel on Climate Change hit the headlines with the release of its Summary for Policymakers from its new Assessment Report (AR5). Section D2 of the Summary tells us that the lower limit of the climate sensitivity range has fallen from 2°C to 1.5°C, while the upper limit remains unchanged at to 4.5°C. This would seem to constitute a small degree of good news. However, perhaps more interesting is the change in approach revealed in the footnote:
No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.
This is a notable change from the approach in the previous report (AR4):
‘Equilibrium climate sensitivity’, is likely to lie in the range 2°C to 4.5°C, with a most likely value of about 3°C. Equilibrium climate sensitivity is very likely larger than 1.5°C.
So the IPCC have broken with their previous approach, opting not to present a single number as the most likely figure for sensitivity, instead relying on reporting a range of likely figures.
The AR5 Summary doesn’t go into any further detail about the new developments which render cross-study comparisons of sensitivity studies invalid. We will have to wait until Monday for that. However, what does the absence of this number mean for policy decisions?
‘Just one number’
In his presentation at STEPS Centre earlier this year, Roger Pielke Jr. discussed a couple of examples of how policymakers express a preference for ‘just one number’ rather than the range of certainties and error bars which scientists are most comfortable with. In particular he quotes from the Danish Prime Minister speaking to scientists before the Copenhagen Climate Conference, expressing a desire for “fixed targets and certain figures, and not too many considerations on uncertainty and risk and things like that.” In this context, one can see how decision-makers are likely to overlook the IPCC’s careful discussion of various climate models and their range of climate sensitivities and concentrate on their supply of a single number:
Pielke Jr. implies that it is unsurprising that politicians seek to shift accountability from themselves to the expert community through demands for just one number. After all, a decision-maker finds themselves with a lot more criteria to factor in to their deliberations if they are presented with a range of future possibilities, than if they are supplied with a ‘best estimate’. Pielke Jr. argues it is the responsibility of experts to resist decision-makers’ calls to make their choices appear simpler than they are in reality. So while many of the headlines have been grabbed by ‘increasing certainty over human-caused climate change’, perhaps decision-makers find themselves with more policy decisions to take today, as the IPCC has kicked away the ‘best estimate’ crutch.
Enter the sceptics
Monitoring social media chatter from the sceptic community this morning, climate sensitivity has been one of the big topics of interest. Marcel Crok notes that the omission of a ‘best estimate’ is a case of “hiding good news from policy makers” based on the presumption that such a number would have fallen along with the lower limit of the sensitivity range. Andrew Montford was very critical of the decision to omit the estimate, calling it ‘disreputable’ in the absence of any discussion of how climate models have been performing against observed temperatures.
@WarrenPearce Without discussion of model vs obs, it represented attempt to "hide the decline". Disreputable.
— Bishop Hill (@aDissentient) September 27, 2013
Montford provides a good summary of his argument on this here: in short, the models are running hotter than reality. Given this argument, it’s perhaps easy to see why sceptics smell a rat on the sudden non-appearance of the best estimate, as lowering the figure cold be interpreted by some as an admission that climate models have not proved up to the task of predicting temperature change accurately.
More certainty about uncertainty?
However, maybe the real story is that the IPCC should never have published such a best estimate in the first place. How much more does one number tell us about what to do (or not do) about climate change, than a range of numbers? And how justifiable is the process of simplification down to that one number? While sceptics may question some of the circumstances around the disappearance of the best estimate, they may welcome it in the long run as an attempt by the scientific community to claim back standards of scientific reporting around uncertainty, and hand back to politicians the decisions about what to do within those parameters.
Maybe, but I suspect you’re making too big a deal of of this whole one number thing. If anything, simply providing a range doesn’t really tell you have the values are distributed within that range. Is it even, or skewed in some way. Ideally you need to know this in order to weight whatever calculations you’re going to make with regards to how climate sensitivities should influence future policy. Even in the past, they didn’t simply publish a best number without a range. The range has always been presented. At the end of the day, I’m confused at to why people would want to present less information rather than more. It may well be that it’s hard to do something more precise given the different lines of evidence, and that may be why it hasn’t been presented but I’m not sure why this should be seen as a good thing.
Policy makers don’t rely on climate sensitivity numbers, I bet few of them know the difference between the various kinds, transient, effective, equilibrium, earth-system etc. More important and easier to understand are most-likely average temperature predictions for a given date and a given scenario. According to the latest RealClimate blog post, the most likely temperature rise for the biggest emissions scenario is still four degrees C by 2100. No change from AR4.
There’s no decline and no hiding. There’s nothing disreputable there, Bishop Hill, you’ll just have to keep looking.
They don’t know and they’re simply covering their tracks.
Judith Curry is shaking her Ph.D climate scientist head today over the INCREASE in certainty claimed by the IPCC in their latest report: http://judithcurry.com/2013/09/27/95/
This, in spite of the fact that they implicitly acknowledge that their previous best (consensus) estimate of sensitivity was wrong, and their inability to either predict or explain the 16 year halt (not ‘pause’) in the previous global temperature trend. So how, exactly, do you get two fundamental facts of your subject wrong, and then claim GREATER certainty?
Was your question rhetorical or not? There is an answer, I’m just not sure if I should spend the time presenting it or not.
You hit on the key point, its not the range nor the single number that matters but the frequency distribution. IPCC now refuses to publish either the distribution nor their best estimate of one of the key parameters. Of course I am suspicious because of recent studies from observations (not models) which indicate that the distribution of this variable is both highly skewed and with a central estimate not very far away from 1.5 which would not even be an alarming figure let alone a catastrophic one.
IPCC had two major problems with AR5: explaining the pause/hiatus in temperature rise was one but climate sensitivity was the other. They appear to be doing their very best to mislead using accurate data. That is not science, that is politics.
Is it true that they refuse to publish the distribution? What they’ve released today is only the summary for policy makers, so we don’t yet know what is in the report itself. The distributions are also available in the literature. As for the recent observational estimates are concerned, even some of the authors acknowledge that this work is very sensitive to variability in the surface temperature record and in the ocean heat content data. It’s a reasonable bit of work but probably not nearly as robust as many would like it to be and quite likely a lower estimate rather than something we should take as being a better estimate than others that are available.
Your beliefs appear to pre-suppose that the IPCC has an agenda, whereas, in point of fact, its purpose was – and is – solely to summarise the state of scientific knowledge. Sadly, only governments do policy change; and policy will not change until the majority of people demand that it does. Saddest of all, interests vested in the continuance of business as usual know this very well. Thus, just like the tobacco industry did, they perpetuate unreasonable doubt despite increasing certainty in the science (67% in 2001, 90% in 2007 and, now, 95% in 2013); and they perpetuate the false belief that people are in a fight to preserve their liberty. Why is it that so many people can be fooled twice by the same tricks?
The theme seems to be developing that sceptics are stupid for making a big deal about global average surface temperature, and the pause in it.. (ie Carrington in the Guardain, a good example)
Not withstanding it has been THE measure of global warming for 30 years 😉 and there is that very high profile limit the world to 2C Global Air Surface temperature political target…. and the sceptics were of cause discussing the measure, when it paused…
I wonder if this new direction, ways of measuring GW will take a hold?
Marcel Crok notes this footnote (ref sensitivity) in the SPM
16 No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies.
So amongst the scientists there is now no consensus on the consensus any more, ie the previous 3C consensus on sensitivity, they could not now get a consensus figure for AR5
So looks like a big climate science internal ‘debate’ between the modellers vs empiricists.
A further 2- 5 yrs flattish temps in global surface temp, will be interesting,should they occur.
Barry – two excellent observations here. Until the last few years, global surface air T was *the* iconic index to reveal human influence on the system – and of course the global policy goal is terms of global T. As temperature flattened, attention moved first to Arctic sea-ice and now, also, it seems to ocean heat content. In today’s Independent for example of 4 graphs included the one of global T was missing. Unthinkable that this would have happened 6 or 12 yrs ago.
The other point is about the spread betting on the climate sensitivity. If there is now no agreement amongst scientists across lines of evidence it is a great illustration of the futility of relying on consensus claims to coerce the population (cf. Cook et al and the 97% claim). In 2007 there *was* agreement on this crucial index of human influence; in 2013 this is *no* agreement. Was the 2007 agreement premature? Not necessarily – but science often works this way – it doesn’t progress in a straight line towards the truth, but meanders around not quite knowing where it is going to end up. This seems the case of the climate sensitivity – and also the high end of the SL rise scenarios.
I’m glad to see these remarks of dissensus in AR5. I’ll be looking out for more of them on Monday. Dissensus in science, as much as consensus, is of great public value.
Thank you Mike –
Did you see Damian Carrington’s article in the Guardian with respect to the surface temperature measure of climate change?!
“Yet before the ink is even dry critics are trying to obscure this stark message behind a mirage: the supposed halt in global warming over the last 15 years. This willful idiocy is based on the fact that air temperatures at the Earth’s surface have more or less plateaued since the record hot year in 1998.
What critics choose to ignore is that of all the extra heat being trapped by our greenhouse gas emissions – equivalent to four Hiroshima nuclear bombs every second – just 1% ends up warming the air. By choosing to focus on air temperatures critics are ignoring 99% of the problem.” Carrington
‘willful idiocy’?, that it was the sceptics who focussed on global surface air temperature!?
Had he just forgotten the last 30 years? Thus, the IPCC hockey stick graph air temp anomalies icon, most importantly the 2C air temp political target, anything anybody has seen on the media about global warming air temps, are just forgotten? goalpost shift, and it is the sceptics fault for ‘focusing’ on air temps? sceptics are only sceptics, because of behaviour like that by Carrington.
I do not think that sort of reporting has helped over the years, I imagine like political reporting, environmental reporting draws those that are passionate about the subject. But this can lead to reporters going native – see here http://bishophill.squarespace.com/blog/2012/10/3/broken-filter-seminar.html
I spent a couple of days once trying to persuade Louise Gray Environmental journalists of the Telegraph, that she had misunderstood the decadal forecast graph from the Met Office. And I don’t think she was listening at all, because of ‘who’ I was, not what I was saying.
she had tweeted 0.8C since 1850, + 0.43C by 2017 = 1.2 C of global warming! and how silly sceptics were saying pause was continuing according to the Met Office
Even the BBC had a graphic on Newsnight +0.43C by 2017..
see it here:
When the science was actually saying on the actual Met Office web page! that the 2017 projection was 0.43C above the baseline average, ie the projection was about the same as now! I said to Louise, please read this Met Office webpage, to check for yourself, but no.
Not one of them thought, hang on, an extra 0.43C by 2017, that’s half of last century warming in 5 years? and check. Especially as this had all kicked off because of the BBC’s Roger Harrabin, reporting accurately, that the new forecast was suggesting temperatures would plateau to 2017, according to the new Met Office forecast….
Eventually, the BBC/Guardian and Louise agreed I was right (David Shukman) corrected his misleading BBC article, as did Leo Hickman the Guardian, but I think that Only happened, because Prof Richard Betts (and BBC’s Paul Hudson), chimed in to say I was actually right, otherwise they would have ignored me.
Louise has just started hew own blog page, and just come across to me as an environmental campaigner rather than someone who objectively will look at the data/facts.
I personally have said for a long time, that many of the public are not sceptical of climate science, but sceptical of the media version of climate science. An example being Prof Wadham (a consensus outlier) getting all the attention about Arctic meltdown last year (there is a video of him saying that the Met Office was in Denial about the Arctic, and the sad thing was he was sharing the stage with John Vidal (Guardian Environment editor, just back from a trip on a Greenpeace vessel in the Arctic)
An environmental journalist was self aware to write an article a while back, explaining how other journalists/editors perceived environmental reporters as having, indeed gone native, post Copenhagen/climategate emails.
03 Nov 2010 ABC – A stormy forecast for climate change reporting – Margot O’Neall
“….here’s how some senior journalists described what it was like in their newsrooms after hacking:
“sense of betrayal”
thought we’d “gone native”
“you told me the science was settled – and it isn’t!”
“Climate-gate was extremely damaging in many ways. It gave the impression that journalists had been duped. I think in the end it was mountains out of mole-hills but it looked really bad,” said a print journalist.” Margot O’Neall
Did you see Margot’s article.
most sceptics (especially the general public) are sceptical of the media version of climate science, full of ‘climate p0rn’ and that perhaps over half of the environmental reporters have gone native (to some degree), I would say 97%, but I have no evidence for that (my little joke)
I do think with AR5 (post Copenhagen really, NOT climategate), there will be a sea change in journalism, a little more cynical perhaps, harder questions, and environmental activists (or activists)will not get a free pass with the majority of the media any more.
I do hope the media ask why there is no consensus, on the previously high profile consensus value of 3C for sensitivity.
Ref footnote 16 SPM AR5
With the greatest of respect, Barry, your argument would be valid but for three things:
1. There have been other pauses in warming; and yet each decade is warmer than its predecessor.
2. You cannot explain the 40% increase in atmopsheric CO2 since the Industrial Revolution without reference to human activity and, given this 40% increase (i.e. outside the 180-280 ppm envelope of the last 1 million years), the MWP and LIA are utterly irrelevant.
3. You cannot explain the totality of post-Industrial warming unless you concede that this 40% extra CO2 is the primary driver (i.e. because multi-decadal warming cannot be explained by factors operating on shorter-timescale or those that are random).
No, the modelers and empiricists (paleoclimatologists) are in agreement that it’s 2 to 4.5°C, most likely 3°C. It’s only the combination of models with recent observational data that puts the value potentially a bit lower. The problem with that approach is that there are major uncertainties. They’re using a limited amount of data and short-term variability can be confused for a long-term change, the forcings (especially aerosols) have significant uncertainties, etc. If you were to wager, you’d be unwise to put your bet on the latter against the paleoclimate- and model-based estimates.
I’m just going to ignore Prof. Hulme’s consensus comment, other than to say it really doesn’t make sense.
Actually Dana it is 1.5 – to 4.5C now… (not the AR4 value)
and if you read the SPM, you will find AR5 has ‘most likely 3C’ anymore, they could not agree.
which is why we are talking about it…
16 No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies
screen capture if you don’t believe me, or haven’t read the AR5 SPM
oops, meant to say..
you will find AR5 does NOT have ‘most likely 3C’ anymore, they could not agree
Barry, try reading my comment again, more carefully this time please.
Thanks for commenting here again, much appreciated. Your comment brought three things to mind. Any answers you have on 1 and 2 would be v helpful to clarify the science, while 3 is hopefully helpful re dissensus
1. You say that the most likely ECS is 3°C. As the IPCC don’t seem to have come to a consensus on this, is there another good meta-review you could point me to which comes to this conclusion?
2. I’m probably displaying my ignorance here, but it seems as if you are saying that the models are more trustworthy than the observations, because of various uncertainties over short-term forcings such as aerosols. Are you saying these uncertainties will reduce as we move into the future? That doesn’t really make sense to me, as intuitively uncertainties increase as we predict further into the future. Perhaps I am missing something.
3. To try and clarify the dissensus point for you, the argument is that the IPCC reports would be stronger if they incorporated a number of views, rather than attempting to alight on one monolithic view of ‘the science’. Mike Hulme’s short talk on this matter is worth a look here https://www.youtube.com/watch?v=qT02RDqwRyw
Perhaps the best known analogy, if somewhat imperfect, would be the US Supreme Court which always publishes the minority dissenting views alongside the majority judgement. So rather than attempting to squeeze out alternative views, they are brought into the official picture. It will be interesting to see if this is a one-off or whether there will be more of this in the full report.
There are 3 main ways to estimate ECS. Paleoclimate, complex global climate models, and simpler climate models using recent observational data as a constraint. What I was trying to say is that the first two methods agree (2 to 4.5°C, most likely 3°C), while the third method has recently produced somewhat lower estimates in a few studies. Each method has its drawbacks. ‘Skeptics’ focus on the third method because it gives a result they prefer (confirmation bias). It has some serious drawbacks, however. There are significant uncertainties involved, especially in the aerosol forcing and ocean heat content. While OHC measurements are improving quickly, exactly how fast OHC is rising is still an uncertainty. Levitus is the main dataset, but others suggest it’s an underestimate (e.g. see Balmaseda and Trenberth or Lyman).
It also only produces relatively low sensitivity estimates when the last decade of data is incorporated, which strongly suggests the method is overly sensitive to internal variability (because sensitivity should be fairly constant and should not change dramatically just by incorporating another decade’s worth of data).
The other methods have their drawbacks too. Personally I find paleoclimate the most convincing because it’s based on how the climate has actually behaved, while the other two rely on models. PALEOSENS is an excellent paper on paleoclimate-based ECS estimates.
Their main results illustrated here:
General overview of sensitivity studies:
I think I addressed this above. The lower estimates are also model-based. But they incorporate recent data that has significant uncertainties. Also see Dessler’s short video discussing this.
That seems like a strawman argument to me. The IPCC is a summary of all available climate science research. Perhaps the criticism is of their consensus statements, like 95% confidence that humans are the primary cause of global warming? What use is the report to policymakers if it doesn’t establish these consensus conclusions?
Dana: “There are 3 main ways to estimate ECS. Paleoclimate, complex global climate models, and simpler climate models using recent observational data as a constraint. What I was trying to say is that the first two methods agree (2 to 4.5°C, most likely 3°C), while the third method has recently produced somewhat lower estimates in a few studies. Each method has its drawbacks. ‘Skeptics’ focus on the third method because it gives a result they prefer (confirmation bias).”
That is naked framing. If sceptics prefer the third method because of confirmation bias then their alarmist counterparts prefer the methods that produce the higher estimate. It’s easy, climate science, when you can just work out which science is correct based on ‘motivations’.
Either way, it would seem that the consensus isn’t as keen on the paleo and model-based estimates as Dana is.
“What use is the report to policymakers if it doesn’t establish these consensus conclusions?”
‘We don’t know’ is a perfectly respectable consensus statement.
you read my comment more carefully , please.
or better still read the SPM. the range now is 1.5 -4.5 (not 2-4,) and they could not agree a consensus value anymore… there is no consensus 3C published in SPM.
Barry, maybe I shouldn’t speak on Dana’s behalf but he was (I think) referring to the evidence one can find in the scientific literature (or by talking to scientists) rather than what was presented in the SPM. If one reads the literature, I think one would find that most studies suggest a range of 2 – 4.5 degreees and a reasonable “most likely” would be 3 degrees.
This is your usual style. An assertion with no supporting evidence, that turns out to be false. The recent Otto et al paper came up with a figure for best estimate of about 2, and the Lewis paper 1.6, Masters about 2 I think, Bengtsson et al around 2.
Basically right. My response to Warren goes into more detail.
Paul, I didn’t say others don’t exist. I was simply pointing out that the majority of the evidence would support a range of between 2 and 4.5 degrees with a best estimate of 3. There are more then 4 studies that have considered climate sensitivity. The other point of my comment, which you’ve chosen to ignore, was that Dana was probably referring to the scientific literature in general, not to the SPM specifically.
By the way, Paul, I had a quick look at your new blog. Welcome to the blogosphere, but – seriously – Christopher Monckton – UK – Universally acknowledged as a top expert in the field. And you say I make assertions with no supporting evidence.
Still no evidence for your claim then. There is a graph of the results of several recent studies at
I’m delighted that you’ve read my blog (I’ve given up reading yours) but disappointed by your sense of humour failure.
Paul, I’m not sure why you think I’ve had a sense of humour failure. What was I meant to find funny? I completely accept the existence of the studies that you present. I wasn’t disputing their existence or suggesting that they have no merit. I’m sure they do. However, certainly one of them (Otto et al.) acknowledges that their results are sensitive to short term variations in the surface temperature, in the ocean heat content data, and in aerosol forcing.
Here’s a link to a page showing various different studies that show ranges mainly above 2 degrees for climate sensitivity.
Here’s what I think is a very good video by Andrew Dessler suggesting that climate sensitivity is unlikely below 2 degrees
So, yes it is possible that climate sensitivity (by which I mean equilibrium) could be below 2 degrees. However, I do think most studies would still suggest that the equilibrium is likely above 2 degrees and probably close to 3. Assuming that it’s most likely near 1.5 would, currently, seem to be giving undue weight to recent studies that are likely sensitive to short-term variations in the data that they’re using to estimate climate sensitivity.
Paul, my apologies. I think I may just got the joke. Very subtle, so I didn’t at first realise you were intending it to be funny 🙂
Morning everybody! I will be offline for a bit, so I trust everyone will have a robust, but reasonably polite discussion around the topic of climate sensitivity and/or the effect of the IPCC’s actions in the policy world 🙂 No off topic comments please…
Am I missing something here? Reviewing the ‘literature in general’ is surely the IPCC’s job. One cannot reasonably stress the importance of consensus/IPCC, but then, when the consensus/IPCC does not produce what is expected, instruct people to take a selective view of the ‘literature’.
Similarly, Dana emphasises the importance of expertise in the climate debate. But when that expertise doesn’t — per Hulme, Curry, Pielke — adhere to the desired narrative, it is not longer fit for purpose.
If the SPM no longer seems adequate to the job of crystallising the scientific literature, and expertise is not allowed to deviate from the position defined by Wotts/Nuccitelli, we’re no longer talking about science.
One way of moving past statements from scientists, or from attempts to review ‘the scientific literature in general’ when they apparently don’t ‘make sense’ or challenge our perspectives is to interrogate or challenge them. But this creates a problem for Consensus Policing: If you do not permit challenges to consensus on any basis, either from within or without, you necessarily eschew the scientific method.
More broadly, across debates about climate science and politics, a healthy, Socratic dialogue is absolutely refused by a number of people involved in climate policy. Such institutionalised intransigence is not merely grist to the climate sceptic mill, it is its mother.
If the IPCC has determined that there is no best estimate of climate sensitivity to give to policy-makers, one cannot defend the proposition that CS *is* important while maintaining the argument that the IPCC process (or consensus) is fit for purpose (the purpose being an organisation/process which can provide a summary of the best evidence to policy-makers).
George Monbiot has returned from his own climate change hiatus to announce that the IPCC presents a more conservative picture of the climate than reality. Yet he speaks in no uncertain terms about anyone who would deviate from the consensus position. He wants to sustain his cake and eat it. Others seem equally — and wilfully — immune to their own logic.
Ben, Dana was specifically referring to modelers and paleoclimatologists. If you were to look at the literature I think you would find that most of these studies do indeed regard the likely range as being between 2 and 4.5. So, yes there are new studies (mainly using recent observations) that have brought the bottom of the range down to 1.5 degrees. This may indicate that it is smaller than other studies indicate (which would be a good thing) or it may be a consequence of the short time periods being used by these studies making their results more sensitive to short-term variations in the datasets that are used. I hope that it is indeed closer to 1.5 than to 3. The evidence, at the moment, would suggest that that is unlikely. Assuming that it is likely closer to 1.5 than to 3 would, in my opinion, be overly optimistic (especially as even the SPM gives the range as 1.5 – 4.5).
“If you were to look at the literature I think you would find…”
I think you have missed the point: that it is the role of the IPCC to define the consensus, by looking at the literature, and that we are encouraged to observe the consensus. It doesn’t matter what you think I will think once I have read the same literature as you. Indeed, I know precisely from my own looking at the literature that it suggests a range wider than you (or the IPCC) suggest. However, I don’t expect you to be convinced merely by what ‘I think you’ll find…’, as I have found.
“The evidence, at the moment, would suggest that that is unlikely.”
The evidence, if the IPCC’s advice to policymakers is to be taken as representative of the evidence, is that it is not possible to make an estimate, given the disagreement discussed above. Simply asserting otherwise — that you know better than the advice offered by the consensus — defeats your own arguments that have emphasised the value of the IPCC, the evidence, the consensus, etc. Moreover, picking and choosing in that way seems like an attempt to move the discussion back to technical, scientific points, when it is really about the process by which those points have been produced, and the expectation of it.
Ben, I was being quite specific. If you look at the paleoclimatological studies and at modelling studies you will likely find a range of 2 – 4.5 degrees. I completely agree with you that you can find other studies that show a wider range and some that show much smaller values for the bottom of the range. I’m not disputing that in any way.
I’m not really trying to make any kind of argument as such and I’m not really asserting anything. I was simply pointing out that there are many studies that would support a range of 2 – 4.5 and that would support a likely values of around 3 degrees. However, as you point out, the range presented by the IPCC is 1.5 to 4.5. We, therefore, cannot rule out the possibility of the ECS being around 1.5 degrees. I would argue, however, given this range that assuming that it is likely 1.5 is overly optimistic. Basing our policy on an assumption that it is likely 1.5 would, therefore, also seem overly optimistic. You, of course, are welcome to draw your own conclusions though.
“Basing our policy on an assumption that it is likely 1.5 would, therefore, also seem overly optimistic. You, of course, are welcome to draw your own conclusions though.”
If we’re talking about policy, nobody is welcome to draw their own conclusions though, though; we’re all obliged to the policy.
I’m confused about your confusion about not making an argument/assertion, which would be a ‘this page is intentionally left blank’ claim. The non-inclusion of a best estimate appears, from the SPM itself that there is not sufficient agreement to make a best estimate. This has the consequence of highlighting a wider disagreement in climate science as well as demonstrating a problem with expectations of the IPCC. You say basing policy an an ‘assumption’/estimate of 1.5 is optimistic, the IPCC says ‘we can’t tell’. If 1.5 is an assumption, so is 4.5 and all values between.
So what do we do? Do we presume, opposite the ‘optimist assumption’ is a pessimistic assumption of 4.5, and that the balance between optimism and pessimism lies at the precise centre? Is that what the consensus is? Is it just a matter of finding the mid-point between a range of possibilities? So what does it mean to say we’re 95% sure of it?
Ben, I think we’re entitled to express an opinion with regards to policy. We’re just not entitled to insist that that is the policy that we should follow though.
My comment with regards argument/assertion was simply an attempt to suggest that all I’m doing is making a comment and expressing a view based on my understanding of the scientific literature. If you think that qualifies as argument or assertion, that’s fine.
I guess, I’m slightly confused as to what you’re suggesting or if you’re suggesting anything at all. The range presented is 1.5 to 4.5 degrees. Firstly, this is from the SPM so do we know that they won’t present a best estimate in the actual report? I don’t know the answer to this. My basic suggestion was that assuming that it is likely near the bottom of the range would seem overly optimistic. Similarly, assuming that it’s near the top would seem overly pessimistic. Should we assume it’s near the middle? I don’t know and that’s not actually what I’m suggesting. Given that all estimates actually produce a distribution, producing some kind of best estimate would seem possible, although how to combine the different estimates may be what is those involved can’t agree on.
I would like to think that we’re not going to simply throw up our hands and say “well we can’t tell anything from this, so let’s do nothing for the moment”, but maybe that is what some are concluding from this.
I doubt they will put forth a best estimate in the report. Reason being that there are basically 2 methods that agree, 1 that disagrees, hence there’s no longer a consensus on the best estimate. So I can understand why they left it out. I discuss further in my response to Warren’s comment.
“we’re entitled to express an opinion with regards to policy” – well the issue was science. The context was scientific advice policy-making. Hence, it seems absurd to say ‘we’re all entitled to our opinion’ (or somesuch) in a discussion about policy, since the only people suggesting otherwise are typically Policing the Consensus, or otherwise jumping on the expression of opinion. I digress.
“this is from the SPM so do we know that they won’t present a best estimate in the actual report?”
It is of no consequence, since the SPM is guidance for policy-makers, hence the ‘Summary for Policymakers’. If it’s not in the SPM, the consensus is that climate science cannot produce a best estimate sufficient to inform policy-making. QED. The same points about the problems of non-agreement were also discussed at the press conference.
Ben, yes “[t]he context was scientific advice policy-making” and that was the context I intended when I said “we’re entitled to express and opinion with regards to policy”. Given that my earlier comment had been an “[b]asing our policy on an assumption that it is likely 1.5 would, therefore, also seem overly optimistic,” I had assumed that I didn’t need to explicitly state that the opinion I was expressing was related to what scientific evidence to use when deciding on policy.
It seems to me that what you’re suggesting is that the lack of an agreement with respect to a best estimate introduces a level of uncertainty that means that we can’t trust climate sensitivity estimates when making policy decisions. Is that a fair representation of what you’re suggesting?
No, I was pointing out that you (and others) seem to want to eat your cake and sustain it — where ‘cake’ stands for what is and what is not part of the consensus that informs policy-making.
“….the lack of an agreement with respect to a best estimate introduces a level of uncertainty…”
Uncertainty has nothing to do with it. It’s either in the consensus (SPM), or it’s not. It’s not in the consensus, and the reason for its non-inclusion has been given by WGI. It doesn’t matter what I think should or shouldn’t be in the consensus, because ‘consensus’ isn’t an important concept to *my* argument, which is that it precludes an understanding of, and discussion about what to do about climate change.
Ben, I do think you’re over-interpreting what I’m saying and rather guessing at what I want. What I want (or would like) is for climate sensitivity to be low. What I’m suggesting, in the comments I’ve made so far, is that assuming that it is low is over-optimistic. Most evidence would suggest that it is likely above 2 degrees. Given this, it’s my view that basing climate policy on an assumption that climate sensitivity is low would be unwise and not consistent with the current evidence.
I’ve got to say that I’m somewhat confused as to why you’re including some kind of discussion of consensus and how this discussion benefits from you trying to point out what you think I (and others) seem to want. What I (and others) want is – I would have thought – irrelevant. What is relevant (and what I think I’ve largely focused on in my comments) is the scientific evidence.
Yes, it seems obvious that you are confused — mostly about the IPCC and the SPM.
Whether X degrees is too high or too low an estimate of CS is completely immaterial to the discussion.
You seem to confuse the IPCC AR SPM and discussions about it, the process of producing and interpreting it with ‘the scientific evidence’. The IPCC is not ‘the evidence’. One can’t interrogate the expectations of the IPCC/consensus by arguing the toss about the actual best estimate of CS — there isn’t one any more.
Ben, my apologies. I hadn’t appreciated that there were a set of rules as to what I’m allowed to discuss and what I must not mention. I didn’t realise that now that the SPM has been publised, we’re no longer allowed to consider the actual scientific evidence, but must instead stick rigidly to what is said in the SPM. As you mention, I am clearly confused, as I really did not realise that the SPM now defines the consensus that we must all follow. My mistake and, once again, my apologies for getting this wrong. I shall endeavour to do better in future now that you’ve enlightened me with regards to what is acceptable and what is not.
Nobody said anything about you not being allowed to. But it seems to be off-topic, in spite of Warren’s request that discussion relate to the blog post above.
Necessarily, if there is no consensus on the best estimate for CS, there is no best estimate. Discussing what it might be, in a conversation about the expectations of science/the IPCC process to produce single numbers seems to be daft, not just off-topic. It’s not unlike arguing about how many unicorns would be in a field if they did exist, subsequent to having established that they didn’t exist, and that all talk of unicorns was a bit of a distraction from the real world.
But by all means, please don’t let me stop you going on and on about what the ‘real’ (but non-existent) best estimate of CS is. Just don’t complain when I say that going on and on about it is a symptom of your confusion about the debate you make a lot of noise about.
Ben, how can it possibly be off-topic to discuss “best estimates” for climate sensitivity in comments to a post about the significance of the IPCC no longer providing a best estimate? You appear to be saying that them not providing such an estimate now means it no longer exists and therefore we can no longer discuss it. Is that a fair assessment of what you’re saying?
However, if you actually go into the literature (which you also seem to be suggesting is no longer appropriate) you will discover a number of methods for estimating climate sensitivity. These methods all provide best estimates. The issue appears to be that they cannot (at the moment) be combined so as to give a single best estimate. So, yes we do not have a single best estimate based on a combination of all the different methods, but we do have best estimates for the different methods and discussing this issue would seem highly relevant to this post.
No, I explained why I prefer paleoclimate estimates, for example. Paloeclimate also has the advantage of being based on large changes (much larger than the anthropogenic change to date), and having many different examples for comparison (as opposed to the effective sensitivity estimates that are only based on the one example of the past ~century). It’s hard to come up with valid reasons why the recent estimates are more reliable than those from paleoclimate or complex models. One obvious exception being confirmation bias, of course. If you have a better justification, please enlighten us.
“If you have a better justification, please enlighten us.”
Sure. I think sceptics broadly have a preference for temperatures being measured in the present, with thermometers, rather than through reconstructions through proxies which may or may not be well calibrated. (I could add a number of things here, but we all know what the justifications and criticisms are). That’s not a sinister preference. It doesn’t betray any malice or motivation. Yet that is how you’ve presented dissent from the consensus.
You draw attention to the fact of your own preferences by dividing the scientific debate on political lines. But a maxim that everybody understands intuitively is that what is sauce for the goose is sauce for the gander. Once you let the ‘preference’ cat out of the bag, everything that follows is special pleading that will only appeal to a diminishing number of increasingly alienated people. In terms of ‘method’, yours precludes a synthesis of what you admit are approaches that do not produce agreement, none of which are sufficient to produce the knowledge we want from them — a conclusion that the IPCC seem to have drawn for the time being.
It’s very easy to pick and chose. My point was that your preference — and its justification — was as transparent as the one you attributed to sceptics. The point is not to argue the toss. The point is that your own loud and angry interventions in the debate preclude a sober dialogue about the demerits of any technique, the consequences of their results, and any possible attempt to mitigate those consequences.
If you hadn’t made such statements, and if you hadn’t helped to deepen the polarisation of the climate debate, it wouldn’t be such a problem for you that the consensus can no longer produce a best estimate of climate sensitivity. And the putative hiatus would not be an obstacle to progress.
How likely is it that all proxies (e.g. tree rings, corals, ice core and seafloor sediment isotope ratios, etc) are poorly calibrated and inaccurate 100% of the time? Irrespective of their accuracy, how likely is that they would all produce the similar graphs revealing overall downward trend over last 6k years ending 200 years ago; after which increase has been 20 times faster than any such similarly-sustained increase in 4.6 billion years? The answer – in both cases – is ‘highly unlikely’.
Rejecting any evidence that conflicts with your world-view (by invoking conspiracy theory) is not scepticism. It is a form of willful ignorance and ideological blindness. As such, it is the territory occupied those who deny the reality of evolution and the age of the Earth.
I liked the comment of Sir Mark Walport (UK Govt chief scientific advisor) on BBC News 24 on Friday morning, to the effect that: ‘Whether or not anthropogenic climate disruption (ACD) is happening is not a subject upon which we can vote; there is a right answer’.
I think the IPCC’s omission of a best estimate value for climate sensitivity is a tacit admission that it no longer matters. As was stated in the press conference, ACD is now the greatest existential threat that humanity faces. David Grist once expressed this sentiment on the Grist blog as, ‘We either do something or we’re screwed’… The US Department of Defense, the International Energy Agency and International Monetary Fund have all said the same thing: Further delay in decarbonising our global power generation systems will not be cost effective (as the longer we take to do it the greater will be the adverse consequences). Even the Communist Party of China has admitted this to itself and its people. I think it is time Western governments did the same.
I have given up trying to reason with people like Barry Woods (who prefer to feign indignation over the use of terms like ‘climate change denier’) but I do wish that he – and all other supposed ‘sceptics’ could tell me why they dispute the reality, reliability, or reasonableness of the modern day consensus regarding climate science? Do such ‘sceptics’ really want us to believe that they are just smarter than everyone else? To put the question another way, do they think the majority of genuine experts are stupid, mistaken, or deceitful? Which is it; and what actual evidence have they to support their beliefs?
Unless or until such ‘sceptics’ come up with an alternative explanation, it would appear that their continuing refusal to accept the near-certainty that humans are causing most of the ongoing warming (ice melting, coral bleaching and die-back, sea level rise, etc) can only be justified by believing that the consensus is either a scientific conspiracy designed to perpetuate research funding or a political conspiracy designed as a pretext to tax people more heavily. Sadly, there is no evidence to support either assertion; whereas there is a great deal of evidence to justify taking seriously the refreshingly blunt warnings from the IPCC.
calm down Martin… you’ll be talking about fossil fuel funded conspiracies next.. as for you giving up trying to reason. you never started.
and i do not ‘feign’ anything, that is your imagination.
What, you mean like the fossil fuel industry funded campaign of obfuscation documented in the movie, Greedy Lying Bastards, Barry? Accusing me of being irrational is no substitute for falsifying the logic of my argument. But, of course, you are only interested in discussing your cherry-picked quanta of data capable of supporting your laissez-faire attitude (plucked from a mountain of evidence that does not).
you said ‘irrational’ not me…
Barry, please stop hiding behind a wall of pedantic obfuscation: You said (of me), “As for you giving up trying to reason, you never started” …How else am I supposed to interpret that remark than as an attempt to suggest I am being ‘irrational’?
Wotts: “Ben, how can it possibly be off-topic to discuss “best estimates” for climate sensitivity in comments to a post about the significance of the IPCC no longer providing a best estimate? ”
All I can say, Wotts, is that you haven’t understood the discussion you’ve got yourself involved in. The unicorns example was the most straightforward way of explaining the problem.
I see, so discussing a “best estimate” for climate sensitivity is comparable to considering the existence of unicorns. I had no idea. My apologies to Warren then for making such off-topic comments.
Not really. The point was that talking about the ‘real’ best estimate is like talking about ‘real’ unicorns when it has been established that they don’t exist. Only the consensus can determine the best estimate. You encouraged people to go and survey the literature, which, you thought we’d find, would reveal such a metric. However, it had already been pointed out to you that the review of the literature had already been done… by the IPCC… and that it had not found one. Thus, determining a best estimate for ourselves would be to contradict the consensus (which is Verboten).
You can say, of course, that the IPCC process is not adequate. But that would put you in the same category as a ‘denier’ — outside of the consensus. The discussion is not about what the BE of CS is. It is about how things like CS ranges or BEs are (or are not) useful to policymaking. So, of course, you are free to say, as often as you like, ‘CS is X’. But it doesn’t seem to relate to any points being discussed here, and is not what I questioned you about. You really might as well talk about unicorns.
Thanks to all for comments so far. Can I pose two slightly different questions?
1. What, if any, difference does the absence of an ECS figure in AR5 make for climate policy?
2. A lot of the discussion has been about whether the search for an ECS figure should take place in IPCC AR5 or in the wider literature. If the answer is the latter (e.g. because of very recent developments in the literature), does that mean that the IPCC AR reports have outlived their usefulness?
“1. What, if any, difference does the absence of an ECS figure in AR5 make for climate policy?”
None. The IPCC — in particular the cycle of Assessment Reports — are ritual much more than they are science. The ritual supplies moral authority — rather than information — to advocacy and policy-making. But the farce of the UNFCCC, the absurdities of EU policies, and the UK’s banal Climate Change Act 2008 owe almost nothing to the IPCC at all, much less an ECS. This much is obvious from the statements made by policy-makers (and even UN/IPCC/FCCC members/staff/authors), which routinely and radically depart from the IPCC ARs and SRs ‘consensus’.
“1. What, if any, difference does the absence of an ECS figure in AR5 make for climate policy?”
Not much. Policymakers may feel that they have a little more uncertainty to address, but there isn’t a one-one correspondence between scientific evidence and policy; and policy doesn’t change as a result of small and subtle changes of presentation in scientific reports. There is a sense that Ben Pile is correct in that the IPCC reports supply a reinforcement and a justification of policy as it is enacted (since it’s obviously appropriate that policy that relates to scientific issues has an important justification in the science!).
So the science and policy making go-hand in hand, and that’s pretty much as it should be. The particular policy enacted (e.g. Germany’s strong drive towards greenhouse gas reduction and renewable energy sources which is now around 25% of total) has a certain inertia of its own which v small changes in the science or its presentation are unlikely to influence.
“2. …does that mean that the IPCC AR reports have outlived their usefulness?”
Really?! The whole point of scientific input to policy is that the science and its implications are addressed faithfully and in its entirety, especially in the case of climate change where the scientific imperative to policy response relates to surface warming, glacier and ice cap melt, sea level rise, ocean acidification, hydrological cycle changes, extreme weather intensification, and so on. The idea that the IPCC reports “have outlived their usefulness” because the ECS is presented with a greater level of uncertainty that in the previous report is pretty silly.
I haven’t read the discussion on this thread fully, but I suspect that the saner side of the argument relates to the fact that the issues are rather more complex that can be addressed in single sentences and short paragraphs in the Summary for Policymakers, and that if one requires a fuller account of ECS as currently understood, a little more work is required (e.g. by reading the relevant sections of Chapter 12 of the full report, especially in relation to Box 12.2 Figure 1, discussions with relevant climate scientists and reference to the scientific literature). One should also recognise that the IPCC reports are conservative and attempt at all-inclusivity. That may be considered either a failing or a bonus, depending on how one looks at these things!
What is that if not a working definition of ‘irrational’? As usual, you are hiding behind a wall of pedantic obfuscation.
Are you ‘projecting’ Martin
In what way am I obfuscating anything, or being pedantic, Barry? Granted, I refuse to debate the validity of your cherry-picked data (when you bother to cite it) but that is simply because it has always been previously debunked by others. All I have ever asked you to do is justify your distrust of the 95% confidence the IPCC says it has regarding primary human causation of ongoing climate disruption.
Since our governments clearly do not like what the IPCC tells them, it does not make sense to argue that the consensus is a consequence of political correctness or convenience. For governments all around the World with a vast array of problems to deal with imperil their success at the next election, the consensus of climate scientists – warning that anthropogenic climate disruption will get worse the longer we argue about it – is a very inconvenient reality.
Given all of this, I just want to know whether you think the vast majority of climate scientists are either stupid, mistaken, or willfully trying to deceive governments. Alternatively, if you think there is an alternative justification for remaining ‘sceptical’, then please tell me what it is.
By the way, this comment was not meant to appear here (that is why it is more-or-less repeated above).