Can the ECS be less than 2 degrees?

I thought I would post this video of a talk by A.E. Dessler, that’s being doing the rounds. You may all already have seen it. I saw it first at Rabett Run. The video basically discusses whether or not the Equilibrium Climate Sensitivity (ECS) could be less than 2oC. For those who don’t know, the ECS is the eventual change in global surface temperature if the atmospheric CO2 concentrations were to double. The video explains everything quite nicely, so I don’t really have to say more, but I thought I would make a brief comment.

The video, in a sense, is a very good illustration of how one might undertake a serious discussion about global warming. One could argue that the global quantity we would most like to understand is the ECS. It tells us how much hotter the planet will eventually get given a certain rise in atmospheric CO2 concentration. How would one step through such a discussion about the ECS? Well, I suspect that if you were to question a large number of climate scientists, almost all (if not all) would agree that – in the absence of any other changes – a doubling of atmospheric CO2 would increase the equilibrium surface temperature by about 1oC. This has been tested in laboratories, there are satellite measurements of changes to the outgoing spectrum, and you can play yourself with the MODTRAN code. I know there are no scientific facts, but this is probably pretty close to being one. There is very strong agreement about this.

Now CO2 concentrations can’t simply change without other things changing too. The net change to the equilibrium temperature if CO2 concentrations double is not going to be 1oC. It could be higher, or it could be lower. However, past climate history tells us that there is no evidence that the net feedbacks can be negative. In other words, there is no evidence that a doubling of atmospheric CO2 can lead to an eventual change in surface temperature of less than 1oC (there are probably also quite good heuristic arguments as to why this isn’t likely). This, I suspect, would also be almost completely accepted by active climate scientists today. In fact, paleoclimatology evidence suggests that the ECS is probably quite high, closer to 3oC (or higher) than to 1oC. So, in a sense one could establish – at this point – what most (if not all) current climate scientists agree. The ECS is certainly bigger than 1oC and almost certainly bigger than 1.5oC.

Now we come to what the video discusses in more detail and probably does a better job of than I can do. Current evidence (and past climate history) tells us that as atmospheric temperatures rise (due to increased CO2 concentrations) we will see increases in other greenhouse gas concentrations and in atmospheric water vapour. The influence of these are also understood well and so most climate scientists would agree that if you add the effect of increased CO2 to the effect of increased water vapour and other greenhouse gases, the ECS rises to about 2oC. Maybe there isn’t as much agreement about this than about the effect of CO2 alone, but I suspect the agreement amongst climate scientists is still strong.

Now we get to areas that are not as certain. The effect of clouds, for example. Clouds can both have a positive and/or a negative feedback (increase albedo but also absorb long-wavelength radiation). However, again the evidence does not support that the net effect of clouds is to provide a negative feedback that would reduce the ECS below 2oC. Increased surface temperatures will also reduce polar ice and reduce albedo, increasing the absorption of solar energy. Effectively, most evidence suggests that the feedbacks are positive and that the ECS has to be bigger than 2oC. So, there is “complete” agreement about the ECS being greater than 1oC, very strong agreement that it is bigger than 1.5oC, and most climate scientists would probably agree that it is likely to be greater than 2oC.

However, this isn’t really what I’m trying to get at here. If people were genuinely interested in understanding the science, they would be willing to listen to the type of argument presented in this video, which quite nicely shows what scientists think they understand well and are confident about and what they understand less well and are less confident about. Doing this would give a better sense of what we can be confident will happen, what might happen but we’re less sure about, and what is unlikely to happen. This doesn’t mean you have to ultimately agree with the scientists. They could be wrong. But if they are, they’re wrong about some fairly fundamental things and one would need to show that these fundamental things were wrong if one was to significantly contradict our current scientific understanding of global warming.

So, in my opinion, the debate isn’t possible if people aren’t even willing to actually listen to and understand the evidence. I’ve been writing about this for about 5 months now and I’ve been trying to remain civil and have been trying to engage with anyone who’s willing to discuss this. I don’t even care if we never actually reach an agreement. However, the more I engage, the more I encounter people who completely dismiss the evidence without even attempting to show that they actually understand it, or have tried to understand it. My intention is certainly to remain civil, but this will partly be done by simply ignoring those who’ve illustrated that they’re unwilling to consider that the evidence might have any merit. An ever increasing list of people, unfortunately.

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37 Responses to Can the ECS be less than 2 degrees?

  1. Rachel says:

    Good video. I hadn’t seen it.

  2. BBD says:

    As I understand it, there would be quite severe difficulties explaining how orbital forcing actually terminates glacials if ECS is less than ~2C.

  3. BBD says:

    However, this isn’t really what I’m trying to get at here. If people were genuinely interested in understanding the science, they would be willing to listen

    But they are not interested. They are deniers. Far from an Holocaust-invoking pejorative that must never be used, this is an accurate description of the behaviour on display. And I bitterly object to their almost successful attempt to hijack the language and make the use of this term problematic. If they are allowed to control the language, they have achieved an underhand, unfair advantage. And not for the first time. Remember what happened to the term “sceptic”.

  4. I believe that’s correct. What I took from this video, though, was that even if you ignore the paleo record (which it essentially does) the evidence that we have today still supports that the ECS is greater than 2oC.

  5. Yes, I’m heading very rapidly in the same direction as you. What some of my recent posts have been trying to argue is that what’s worse is that some commentators, who should know better in my opinion, are starting to suggest that we should be giving the “skeptics” more credence and should engage more with them. So, not only have they hijacked the language, they’ve even managed to convince some that they should be given an even more prominent platform. The view that I’m starting to develop is that society would be better served if we didn’t allow vocal lay-people to dominate a complex scientific discussion.

  6. I should also add that even I’ve fallen into the trap (at least I’m aware, I guess). I don’t want to use “denier” (even if it does apply) and so have ended up using skeptic/sceptic.

  7. BBD says:

    For a time, I avoided the term altogether, then I realised that I was being manipulated and compromised by doing so. When appropriate, I will use it nowadays.

    The creeping legitimisation of climate change denial and deniers is, as you say above and on the other thread, not a welcome development. There are too many pundits with weak topic knowledge and – surprisingly – little apparent awareness of how clever liars manipulate the system to gain advantage. As you say, they are not serving society well by enabling denial.

  8. BBD says:

    Of course. I tend to point to paleoclimate behaviour reflexively as so much denial is based on rejecting the models and misrepresenting the true, systemic nature of modern warming and blithering on about pauses etc.

  9. chris says:

    When someone complains that the word “denier” is a Holocaust-invoking pejorative it’s worth pointing out that some of the more prominent so-called “skeptics” are quite comfortable to self-identify as “denier”s, e.g.:

    David Bellamy “I am a denier, and proud to be one”. Dr. Bellamy was talking in response to questions on his views on climate science and so the context of his comment is clear (even if his opinions on climate science are/were ill-informed).

    Dr. Richard Lindzen quite likes the term:

    For his part, MIT’s Lindzen told the BBC in 2010 that he rejects the “skeptic” label because it should be reserved for situations where one is contradicting a “strong presumptive case,” which he insists is not the case with climate change. “I like ‘denier,’ that’s closer than ‘skeptic,’” he said when asked about labels he preferred for himself. “Realist is not bad.”

    Rather in contrast to the faux-concern, Dr. Lindzen is Jewish and in fact his parents fled Nazi Germany to arrive in the US. It really doesn’t take superhuman wit to deal rationally with the semantic context of words.

  10. I ended up in a Twitter discussion with someone who associated using the term “denier” with terms associated with race, or disability. The idea that describing what someone has openly chosen to do (i.e., deny something) with pejorative words that are based on a characteristic that someone has no control over, is just absurd.

  11. The term denier is accurate. These people are in complete denial of reality. If they had not brought up the topic, I had never, ever thought of the relation with Holocaust deniers.

    My impression about most is that they do not like mitigation policy and therefore deny the science. This is illogical and you can also accept the science and still oppose (certain) policies.

    A compromise term could be climate ostriches. No Holocaust, still clear denial.

    The term “sceptics” is a complete misnomer. I have never met people in my life that are so uncritical with respect to their own ideas as “sceptics”. I can only use that term with quotes, would get psychological and stomach problems otherwise. The moment the majority of real sceptics from sceptical societies join the fake “sceptics”, I will rethink my position. I am sure this will never happen. These groups are antipodes.

    On the other hand, if I comment on “sceptical” blogs, I try to avoid those words, as these words will be abused to avoid discussing the science.

  12. plg says:

    I strongly dislike using “skeptic” since it is being hijacked as pointed out above. However, I also feel “denier” is not enough, since we need to distinguish between people who just deny climate change for whatever reason and people thain addition to denial also vigorously try to convince others (proselytizing?). There is another term I haven’t seen used but feels appropriate: bigot.

    Merriam Webster:
    “a person who is obstinately or intolerantly devoted to his or her own opinions and prejudices; especially : one who regards or treats the members of a group (as a racial or ethnic group) with hatred and intolerance ”
    “a person who is utterly intolerant of any differing creed, belief, or opinion.”

    Having said this, I guess using the term “climate bigot”, although accurate, may offend people other then the vigourous deniers.

  13. I agree about sceptic and I think I have used it a bit too liberally in some of my posts.

    Someone, on Twitter, has suggested that maybe “rejectionist” would be suitable. Can’t see any reason why it would be seen as pejorative. Maybe it’s not quite strong enough though.

  14. BBD says:

    Contrarian when unprovoked, denier when it becomes unavoidable and necessary.

  15. Pingback: Can the ECS be less than 2 degrees? | thejaminthemiddle

  16. Warren Pearce favorited this:

    Therefore I think I am right.

  17. D. Brookman says:

    Victor’s “ostriches” is an excellent suggestion.

    Like it or not, the deniers are able to score points with the use of “deniers.” Take that away from them. Let’s promote use of “contrarians” in formal settings and “ostriches” elsewhere.

  18. ECS only includes fast feedbacks such as added water vapor due to heat.

    ECS does not include so called slow feedbacks such as albedo change and the emptying of natural carbon stocks back into the atmosphere.

    According to paleoclimate, total Earth systems sensitivity is at least double current ECS estimates. In an example of this, a very small forcing from orbital changes at the end of the last ice age resulted in an Earth Systems response of +100 ppm CO2 and a 5 degree C temperature increase. There’s now way to get there through current ECS measures alone.

  19. dana1981 says:

    Well, Lindzen and Spencer have both argued that ECS is close to or less than 1°C. But obviously they’re outliers.

  20. Yes, they are obvious outliers and were the people I was thinking of when I wrote “almost all”.

  21. I assumed this was why the recent Otto et al. (and Nic Lewis’s) work was giving lower ECS values than other estimates. Some estimates come from detailed modelling which presumably can include some of the slow feedbacks. Otto et al. simply used current (the last few decades) measurements of temperature changes, estimates of changes in forcing, and estimates of changes in the ocean heat content. This almost certainly ignores any long-term effects.

  22. Rob Painting says:

    Otto et al (2013), a lowball estimate, already precludes climate sensitivity below 1.2°C IIRC. So warming has already excluded Lindzen & Spencer’s estimates – as one would expect due to the implications of paleoclimate.

  23. Thanks Rob, yes that makes sense. What I was trying to get across in the post (maybe not all that clearly) is that if people were genuinely sceptical (in a good way) they could watch videos like the one here and talk to climate scientists (or read SkS) and discover what scientists are fairly certain about (ECS not less than 1.5oC), what they’re fairly sure of (probably not less than 2oC) and what they’re not as certain of (maybe as high as 3oC). That supposed “sceptics” are not engaging in such discussions leads me to believe (may have been obvious to some for a long time, but I’m new to this) that they really don’t want to understand the scientific evidence.

  24. The point here is that even the most complex ECS models leave feedbacks out and that, in the literature, ESS has been a measure used to assume all ‘slow feedbacks’ even though this has been very difficult to model. The recent Hansen paper finds Earth Systems Sensitivity to be as much as 7 degrees C or more once all the feedbacks are taken into account, with 6 as a median range, for a doubling of CO2. The 6 degree C number correlates well with best observations of proxy temperature data during the Pliocene and earlier. A recent paper that included ice free states during the Pliocene found temperatures that were near proxy values. So at least in that case added albedo change provided the 2-3 C temperature rise we see during the Pliocene when CO2 values were between 360 and 405 ppm.

  25. Thanks, I hadn’t appreciated that subtlety.

  26. chris says:

    Since science is supposed to be about evidence, it would be good if those people that consider Lindzen and Spencer the “go-to” sources for climate info (or “climate info balance”) might consider querying their (Lindzen/Spencer’s) evidence in support of very low climate sensitivity.

    It doesn’t seem to come from their publications. Neither has published any significant science on the subject in the last two years, and their work up to that point (2011) has been shown to be either uninformative on the subject of climate sensitivity or seriously deficient. Clearly these two individuals feel fervently that climate sensitivity is low and try extremely hard to find a scientific justification for their opinions. That’s fine scientifically-speaking (after all reality is the final arbiter). But we’re being cheated as voting members of the public if their opinions are considered to provide some sort of counter to the prevailing evidence that informs the consensus on climate sensitivity.

    I’m waiting for the day when some bright science journalist is struck by a flash of inspiration and notices the astonishing dichotomy between the latitude afforded to a tiny handful of scientists whose fundamental contribution to climate science during the last 15-20 years has been getting things hopelessly wrong (apparently in pursuit of scientific justification for a preconceived view), while the blogospheric vilification of climate scientists who work their socks off to advance the field, spills over into the “pukka” media.

    Would have thought that was a subject worthy of consideration by sociologists and “experts” of social policy, if they ever consider venturing outside of their comfortable “asset” and “deficit” “model” viewpoints.

  27. Chris, you’re mixing posts here 🙂 but indeed that was one of the points I was trying to make in my “deficit vs asset model” post. If those interested in science communication wanted to actually contribute to improving the public’s (and policy makers’s) understanding of climate science, the best thing they could do now would be to convince them to stop listening to the fringe element (or, at least, give them far less of a hearing) and start listening to actual climate scientists. Once they done that they could then move on to discussing how best to communicate actual climate science.

  28. chris says:

    Thought I was on topic since there’s not a lot of support for v. low ECS outside of the tiny group of “proven-wrong” science advocates we’re discussing.

    But all of these subjects mix together don’t they? Discussion of Drs Lindzen and Spencer invites consideration of ECS (they assert about ECS even if they don’t provide viable evidence), falsifiability (many of their their opinions have largely been falsified in the Popperian sense), Tamsin-Edwards-style advocacy (are there any stronger advocates for policy amongst the scientific community than Lindzen/Spencer?) and “asset” “deficit” “models” (affording equal weight between their opinions and the large evidence-based consensus enforces an unfair and undemocratic deficit of knowledge amongst the public).

    Ultimately a lot of this boils down to something rather simple – misrepresenting the science on subjects of profound interest to Joe and Josephine (Joelene?) Public is disgraceful and damaging as we’ve discovered many times before. Perhaps that’s a lesson that’s fundamentally unlearnable in the modern world – or maybe we always do learn it but always a little or a lot too late 🙂 …

  29. chris says:

    perhaps it would be more on-topic to point to a couple of just-published papers in PNAS on climate sensitivity from paleo- and long time scale-perspectives…


  30. Tom Curtis says:

    I think the methodology in that Hansen paper is very suspect. He treats GHG forcings between the modern era and the last glacial maximum as the only forcing, with all else being considered as feedbacks on the GHG forcing. However, we know the temperature rise from the LGM was not initiated by a change in GHG concentrations. Therefore we know the changes in albedo were not just consequences of GHG concentrations, thus falsifying Hansen’s essential assumption.

    Further, if the method was correct, it would be equally valid to take albedo changes as a given, and treat changes in GHG concentration as a feedback on changes in albedo (which to large part they were). Doing so would give a different and lower value for ESS.

    Having said that, values of 6 to 8 degrees per doubling of CO2 are common in paleological studies of ESS, with the caveate that values tend to be significantly lower when there is little or no polar ice.

  31. Or how about mainstream versus cold fringe?

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