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Bishop Hill Sep 26, 2014 Climate: sensitivity One criticism of the energy budget model approach that lies behind these kind of studies is that it doesn't take into account the role of the oceans in taking up excess heat. Other estimates of climate sensitivity using climate models support the higher end of the IPCC's likely range.
Carbon Brief is struggling again.
Bishop Hill Sep 24, 2014 Climate: sensitivity Nic Lewis and Judith Curry have a new paper out in Climate Dynamics and report that climate sensitivity is even lower than previously thought. There is a long but somewhat technical writeup at WUWT, so this is my attempt to explain it all in layman's terms.
There seem to be two main strands of innovation in the paper. Firstly Nic and Judy have used the estimates of ocean heat uptake and radiative forcings reported in the Fifth Assessment itself. Secondly, they have made their energy budget approach somewhat more sophisticated in order to deal with the twin problems of volcanos and natural cycles.
Bishop Hill Aug 28, 2014 Climate: sensitivity In my post about Keith Shine's contribution to the All-party Climate Change Group briefing on AR5 I said that Prof Shine had failed to discuss the divergence between model and observational estimates of climate sensitivity. In fact the report on which I had based this statement (and which I quoted in the original piece) misrepresented what Shine said. There is an audio file available here (H/T Richard Betts) which shows that a significant chunk of the talk was in fact given over to a consideration of the two main approaches to estimating climate sensitivity. Shine described the pros and cons of the various approaches as follows:
...state-of-the-art climate models, which are our embodiment of the laws of physics as applied to the atmosphere...
...a mixture of observations and simple models. Now you might think using observations were a better way of doing things but the problem is that there are a lot of things going on at the same time in the climate system - the internal variability, the aerosols - and there is also a lot of debate about how you should do your statistics to estimate the climate sensitivity.
I'm not sure I detect any question marks over the reliability of the models. No mentions of fudge either. And the remarks about debates over statistics are grossly misleading. The IPCC has been engaging in PR rather than science: showing a series of studies that all use flat priors in ECS is equivalent to repeated shouting "We already know that climate sensitivity is high". It's propaganda, not science.
So I'm not sure that Prof Shine is giving the politicians a fair assessment here. It looks more like an attempt to pooh-pooh the observational estimates.
Still, if you think this is bad, wait until you see the next post.
Bishop Hill Aug 27, 2014 Climate: Surface Climate: WG3 Climate: sensitivity Richard Betts Richard Betts posted some further thoughts on GCMs and public policy in the previous post on this subject. Since the thread is now heading for 300 comments I thought I'd post his ideas up here and respond in turn.
Richard first set out his understanding of my position.
I'd initially thought that you were claiming that the very need for any kind of climate policy was based on GCMs. Clearly it isn't, for the reasons I stated, but it seems this isn't your point here anyway. You seem to be moving a step further and talking about the importance of GCMs to the details of climate policy (eg. a carbon tax). Here I do partially agree with you - GCMs do of course play a role in the details, as they help with understanding the climate system, but they are by no means the only source of information. Moreover, I don't think the examples you give would be substantially affected if we didn't have GCMs.
Bishop Hill Aug 24, 2014 Climate: Parliament Climate: sensitivity
Updated on Sep 3, 2014 by
Bishop Hill
The parliamentary briefing linked in the previous posting is very interesting. There are several bits and pieces worthy of comment. In this post I'm going to pick up on something Keith Shine FRS told the MPs about climate sensitivity.
- The presentation gave an overview of the fundamentals of the climate system and discussed how sensitive the climate system is to increases in CO2 concentrations. AR5 stated that it was extremely likely that the temperature increase will be between 1.5°C‐4.5°C, although extremely unlikely that it will be less than 1°C and very unlikely of being greater than 6°C.
Bishop Hill Aug 22, 2014 Climate: Oceans Climate: Surface Climate: sensitivity Nic Lewis emails:
I am sorry to see that Piers Forster has given what I consider to be an incorrect statement to the Guardian (p.19) regarding the new Chen & Tung Science paper about the Atlantic storing excess heat. He is quoted as saying: "Most importantly, this paper is another nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down."
The paper very much supports the view of those scientists, including myself, who consider that natural variability in the ocean significantly affects surface warming trends on a multidecadal basis. It does not support the view that a reduction in the rate of increase in radiative forcing caused by aerosols, solar variations, reduction in stratospheric water vapour, etc. is the prime cause of the hiatus.
Bishop Hill Aug 22, 2014 Climate: Oceans Climate: Surface Climate: sensitivity
Updated on Aug 22, 2014 by
Bishop Hill
Overnight the big climate news has been the new paper by Chen and Tung, which seeks to explain the pause in surface temperature rise, now nearly 18 years old on some measures. Judith Curry has excerpts here, while a layman's summary is available at the Economist.
The story goes that much of the missing heat is to be found in the Atlantic, with a slow-moving current speeding up in recent times so that heat is drawn down into the deep-ocean. The theory seems to be that this process runs over a 60-year cycle, for half the time with the depths warming and the surface cooling and half the time the other way round. Chen and Tung conclude that we are currently in a surface cooling phase, so the pause could last another ten years or more.
Bishop Hill Aug 19, 2014 Climate: sensitivity A few days ago I linked to the new Verheggen (John Cook) et al paper, a survey of opinion among climate scientists. A tweet today reminded me of something I had noticed in skimming through the paper which is rather interesting. It concerns climate scientists' views on feedbacks, forcings and climate sensitivity.
At first glance the survey results on ECS are unremarkable, with the modal position being right in the middle of the official IPCC range, centred on 3°C. However, recall that if GCM output is to correctly hindcast the observations, there is a balance to be struck between climate sensitivity and aerosols: to the extent that sensitivity to carbon dioxide is high and therefore warming is large, you have to have a big cooling effect from aerosols in the twentieth century to prevent the GCM hindcast of warming outpacing what happened in the real world.
Bishop Hill Jul 30, 2014 Climate: Allen Climate: sensitivity Nic Lewis has published another paper on objective Bayesian approaches in climate sensitivity study. This looks at an old but very important paper by David Frame and Myles Allen, which implied the use of an objective approach, but actually turned out not to. Lewis's paper looks at two genuinely objective approaches to the problem and compares the essentially identical results they give to the clearly erroneous and inevitably much more alarming one obtained by Frame and Allen.
A very technical blog post on the subject is up at Climate Audit, and the paper is here.
Bishop Hill The House of Commons Energy and Climate Change Committee has released its report into the IPCC's Fifth Assessment Report. This is fascinating stuff, if only to see all the intellectual contortions that have been adopted by committee staffers in arriving at the required answer, namely that everything is hunky dory with climate science and the IPCC.
The press release is here and consists of standard parliamentary cheerleading of the kind that has "sod the constituents" written all over it (Tim Yeo is quoted extensively, so I guess that follows).
Bishop Hill May 30, 2014 BBC Climate: sensitivity Greens ...the need for BBC journalists regularly and systematically to challenge the assumptions behind their own approach to a story, is...difficult to achieve. Even when good intentions lead to specific measures aimed at doing so, there can be inadvertent aberrations. Take, for example, the BBC College of Journalism online service, which includes a whole section on impartiality. First among the clips illustrating the need for impartiality in covering the subject of climate change is an illustrated lecture given by the BBC’s former Environment Correspondent Richard Black. The section of the lecture on the site is entirely devoted to sustaining the case that climate change is effectively “settled science” and that those who argue otherwise are simply wrong. What might have been helpful is for Richard’s talk about the scientific position, and David Shukman’s on the same site, to have included a line or two in which he reminded his audience of John Bridcut’s point, a point made also in the BBC’s Editorial Guidelines, that dissenters (or even sceptics) should still occasionally be heard because it is not the BBC’s role to close down this debate.
Bishop Hill May 27, 2014 Climate: Allen Climate: sensitivity Some readers may have seen Der Spiegel's coverage of the Bengtsson affair a couple of days back. I didn't cover it, as I recall because it didn't seem to add much we didn't know already. However, one interesting wrinkle has emerged today. This revolves around a quote from Myles Allen about the Lewis/Crok report:
Professor Myles Allen, a climate researcher at Oxford, says, "The problem is [GWPF's] anti-science agenda, clearly illustrated by the fact that they refused point blank to submit their recent report criticizing the IPCC 5th Assessment Report to the same kind of open peer review that the IPCC report was itself subjected to."
Bishop Hill May 19, 2014 Climate: sensitivity A couple of weeks ago we discussed the Kummler and Dessler paper, which incorporated something that looked remarkably like a large quantity of fudge, in arriving at an estimate of climate sensitivity of 3.0°C as compared to a still high figure of 2.3°C without the fudge. This prompted a fairly scathing comment from Nic Lewis:
Kummer & Dessler seem to have performed their basic calculations improperly.
They claim that the AR5 forcing time series are referenced to the late 19th century, and therefore deduct from the temperature time series the 1880-1900 average temperature. But the AR5 forcing time series are, as stated in Table 8.6 (which they cite), referenced to 1750. They should therefore have likewise deducted the 1880-1900 average forcing from the forcing time series.
Bishop Hill May 16, 2014 Climate: Sceptics Climate: sensitivity The Bengtsson paper would have to have been very bad to be worse than, say, Kummler and Dessler, but at the moment we just don't know because we haven't seen it. However, the ERL editor claims that Bengtsson's offering contained errors. Unfortunately she doesn't actually identify any; the only concern in the reviewer report published to date seems to be with Bengtsson's temerity in thinking that observations and models really ought to match up, and of course the concern that sceptics might be keen on the paper.
But there are some errors floating around that are worth a look - as I mentioned earlier a cursory glance suggested to me that the reviewer's report itself included a bit of a boo-boo. I've now been away and done some fact checking and confirmed that I was right. Actually, I'm righter than I thought I was, as I shall now explain. Here's the paragraph in question:
Bishop Hill May 16, 2014 Climate: Sceptics Climate: sensitivity The Telegraph has further comments from Lennart Bengtsson, clarifying his position:
Last night Professor Bengtsson, said: “I do not believe there is any systematic “cover up” of scientific evidence on climate change or that academics’ work is being “deliberately suppressed”, as The Times front page suggests. I am worried by a wider trend that science is being gradually being influenced by political views. Policy decisions need to be based on solid fact.
This seems similar to the position advanced by Benny Peiser in his radio interview (see last post), who said that he thought that the problems were caused by a small group of activist scientists.
