The Intergovernmental Panel on Climate Change (IPCC) has just released the Working Group 1 (WG1) report of the fifth Assessment Report (AR5). A difference between what is presented here and what was presented in the fourth Assessment Report (AR4) is that the range for the Equilibrium Climate Sensitivity (ECS) is slightly larger (1.5 – 4.5oC, rather than 2 – 4.5oC) and there is no longer a best estimate. Warren Pearce has written a post on the Making Science Public blog called Just one number: has the IPCC changed its supply of evidence?
My personal view is that this difference is not that significant. The range is slightly larger and the reason why there is no best estimate is, apparently, because there is no agreement as to how to combine the results from the different methods so as to produce a reasonable best estimate. In particular, the more recent observationally constrained results differ from paleo-climatological and modelling estimates. Myself and others made comments along these lines. I, however, ended up in a rather odd exchange with Ben Pile in which he seemed to be suggesting that the IPCC report reflects the consensus view and therefore the lack of a best estimate meant no such estimate existed (he compared discussing it to discussing unicorns). He also implied that actually looking in the literature was no longer reasonable as the IPCC reports now provided the consensus view and that presenting anything that differed was tantamount to being a denier (I thought this would have been seen as a good thing, but maybe only certain people are allowed to question the IPCC).
So, I think Ben Pile is wrong about the role of the IPCC reports. They are not simply reports that indicate the consensus, they are synthesis reports. You may think that this is the same as consensus, but I think there is a subtlety. There is no requirement for everyone involved to agree with all the content of the IPCC reports. It is meant to reasonably reflect our current understanding with respect to climate science. The lack of a best estimate for climate sensitivity may be a prime example. It’s not that such a best estimate is not possible, it’s because there is no agreement as to how to synthesise the results from the different methods so as to produce one. This is not uncommon in science. What is not common is for the different methods to never converge. Just because no agreement can be reached today does not mean an agreement isn’t possible in future. In fact, it would be rather concerning if the different methods didn’t ultimately converge – that would tend to imply some fundamental problem with at least one of the methods.
Anyway, this post has got longer than I intended. What I was really intending to do was highlight Victor Venema’s recent review of the IPCC review. Victor has written a post reviewing what the IPCC report has said about the quality of the land surface temperature observations, Victor’s area of expertise. Victor has also linked to posts by other scientists who have reviewed the aspects of the report about which they have particular expertise. Victor also intends, I believe, to link to newer reviews as they are written. Not all reviews are positive (see Aslak Grinsted’s for example). So, despite Ben Pile’s assertion that questioning the IPCC report is tantamount to denial, some scientists seem comfortable doing so. Personally, I think that this is just healthy disagreements within the scientific community. Would be rather disturbing if everyone agreed with everything. That might make some think that there was a conspiracy or too much groupthink.
Wotts Up With That Blog 
I read a recent op-ed by Michael Mann which you’ve probably seen already – http://www.livescience.com/39957-climate-change-deniers-must-stop-distorting-the-evidence.html – and in it he makes the case for certain projections that differ from the latest IPCC report. I was interested in one of them because it was something I was discussing with someone on your blog recently. It was for sea level rise and Michael Mann says that there’s evidence we will see 2m of sea level rise this century!
Yes, I saw an interview with Michael Mann (by Thomm Hartmann) and I think he was making a similar argument there. We may be underestimating how quickly the Greenland and West Antarctic Ice Sheets may contribute to rising sea levels. In the video he was making the case that we may be close to a tipping point with regards to these ice sheets.
From Victor’s
http://www.glaciology.net/Home/Miscellaneous-Debris/ar5sealevelriseuncertaintycommunicationfailure
http://www.glaciology.net/Home/Miscellaneous-Debris/optimisticicesheetprojectionsinar5
Very interesting counterpoint to “the IPCC is alarmist” meme.
Yes, very interesting. Given that I’m yet to see a credible climate scientist claim that the IPCC reports have over-estimated something, it’s quite hard not to become openly alarmed.
Some day in the future people will criticise the IPCC of today for not being stern enough in their warnings and for failing to mobilise action.
Wotts, thank you for the plug. I hope that helps to get some more reviews of the IPCC report.
“Not all reviews are positive (see Aslak Grinsted’s for example).”
Just to be clear, Grinsted thinks that the IPCC is painting a too rosy picture and that sea level rise could well be much stronger.
You could also claim that my review is not positive. As I wrote, recent work has found a trend bias of 0.2°C in the global mean temperature (the true trend is stronger as the one in the raw data). If you combine this with recent studies suggesting that homogenization algorithms do improve trend estimates, but cannot remove all of the bias. And if you know that the station density over much of the world is not high enough to homogenize very accurately, you may well expect that the real trend bias and thus the real temperature trend is larger. However, I fully understand that as long as this is not well studied and quantified, such as statement would be much to speculative for the IPCC report. It just means that there is work to do for me and my colleagues.
On the other hand, my review is positive in the sense that the text does give an honest representation of the current state of the scientific literature.
The advantage of being very conservative is that you can make statements with confidence.
The scientific “details” are also not important for politics. I do not think it matters.
Somehow I do not think that if the IPCC had written 2 meter sea level rise is possible in 2100, that Saudi Arabia, Exxon, WUWT, Heartland and US republicans would utter an apology for their past behaviour and would stop their opposition.
We have a winner:
That’s exactly where the so-called sceptics are making the mistake. I also find it hilarious that Pile is now hammering that this is the consensus while they’ve been rejecting the scientific consensus for decades.
There is no consensus.
If there was, we wouldn’t know.
If we knew, we wouldn’t be able to spell it out.
If we could spell it out, it would not matter.
H/T to Gorgias:
http://en.wikipedia.org/wiki/Gorgias
No problem, I’d be quite interested to see if you can collect a large sample of links.
Thanks for the clarification. I had intended “positive” to mean the sense that you indicate in your last paragraph, but that probably wasn’t all that clear.
Yes, Ben Pile’s argument that the IPCC defines the consensus when he was previously arguing that Cook et al. was illustrating a consensus without an object does seem rather ironic. The whole discussion was so absurd, I didn’t really know what to make of it (I’m going to refute your argument by telling you that you’re no longer allowed to make that argument). It reminded me of the how does one critically analyse a pile of horse shit? letter that Rachel highlighted a while back.
That was an interesting letter to read.
I just love reading that letter. It always makes me laugh. I love the bit, “It is, in all respects, a dud.” I don’t really understand the point that Ben Pile is trying to make but perhaps we can just regard them as “amusing spam”.
So claiming that ECS is 6C makes one a denier, but claiming it is 0.5C or 0C (as Richard LIndzen and Roy Spencer have done) does not?
I sensed a sort of veneer of sophistry about Pearce & Pile rather than real intellectual heft – it seems to be pretty clear now.
Victor,
if even these “conservative” estimates were have a chance of being widely accepted as a basis for policy, I know that I would sign on the dotted line, and smile.
Actually as I understand Grinsted, his beef is not that the IPCC would be dishonest in reporting the state of the science (but you don’t suggest that), but rather that they are lousy at communicating in a way that is not guaranteed to be misunderstood — accidentally or otherwise. I think he has a point.
Martin, yes that may be a fair way of putting it for the sea level rise. I got the impression that Aslak was somewhat more directly critical of the numbers they’d actually presented for the ice sheets though (although I guess sea level rises and ice sheets are related).
Martin, that is what I was trying to say, whether science, or the IPCC, is conservative or not, it does not make any difference. Maybe in the 1990’ies the uncertainties were still so large that the scientific state of the art was policy relevant.
Nowadays there is no relation between science and politics any more. If humanity/politics fails to take the problem seriously, it is not because of a paragraph in a scientific report or scientific article or even general lack of scientific understanding. (For the details of adaptation strategies, science is important and for human curiosity.)
Thus I would argue that scientists can simply do their work the way they see best and write it down the way they feel comfortable. It is a good tradition to want to be able to make strong claims and thus to be conservative. That tradition is likely productive and furthers scientific progress.
Yes, there is a remarkable amount of irony associated with some of these discussions.
I’ve written before about the Making Science Public blog and am still a little confused about it’s goal. It is associated with research into the role of climate sceptics in the climate science debate. So, maybe the goal isn’t actually to Make Science Public as such, but to simply be a forum where controversial topics can be presented so as to attract a variety of comments (i.e., the blog is driven by a desire to understand the role of skeptics in the debate, rather than by any real desire to aid public understanding of science). I’ve had some reasonable exchanges with Warren Pearce, but I still can’t work out if he is an objective observer, has views about climate science (which would appear – based on his typical retweets – to be on the climate skeptic side), or is playing some kind of role in order to carry out his research.
The latter, he says. It’s an accepted research mode in the social sciences, but IMO offering that guest blog opportunity to Pile amounted to going native.
I too would jump with joy if the latest IPCC report was taken seriously and adopted as a basis for policy. My comment about how future people will criticise the report as being conservative – if this turns out to be the case – was simply because I think this is what humans do. Look at all the criticism climate models get for deviating slightly from observations. If it turns out that sea level rises 2m this century, people will say the IPCC got it wrong.
I can understand the desire for scientists to be conservative but when the worst case scenario is pretty bad, then I think we need to manage that risk. No-one builds a nuclear power plant without reducing the risk of a nuclear meltdown even though the chance of this is minuscule. When there is some chance of a catastrophic outcome, we have a greater duty to reduce that risk.
The other thing I have been thinking about is this image I have of the proverbial scientist who is a quiet, shy and unemotional type and when he finds himself in a crowded theatre and discovers there is a fire, he politely stands up and begins to explain in confusing language that there are sparks of high temperature in the centre left corner of the theatre and it is very likely that we should all carefully and politely leave the building. Sometimes we need to stand up and shout in simple language FIRE, EVERYBODY GET OUT!
So you’re suggesting that Warren Pearce is partly playing a role? I agree though about giving Ben Pile a blog opportunity. Very odd unless, again, it’s just part of the whole research strategy.
> I sensed a sort of veneer of sophistry about Pearce & Pile rather than real intellectual heft […]
You want heft? You can’t handle heft!
Here is heft:
http://neverendingaudit.tumblr.com/post/25231421098
Rachel, also if a scientist states that with high confidence there is very likely a pyrotechnical morbidity problem if the theatre audience follows a business as usual scenario there does not have to be a problem. More communicative scientists, citizens, environmental and political groups can translate this in FIRE, EVERYBODY GET OUT!
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