The equilibrium climate sensitivity... Based on multiple lines of evidence21, the very likely range of equilibrium climate sensitivity is between 2°C (high confidence) and 5°C (medium confidence). The AR6 assessed best estimate is 3°C with a likely range of 2.5°C to 4°C (high confidence), compared to 1.5°C to 4.5°C in AR5, which did not provide a best estimate.
Though to be fair to me I didn't notice anyone else blogging it (because I was asleep in summer? ATTP did, but quietly. Also - whippersnapper - noted that he'd been around at least since AR5. But Gavin didn't mention it in his six-of-the-best, even if he did elsewhere). I notice now because of PF's Twit. Of course, we've known that ECS is 3 oC for some time, but the narrower range is interesting.
Pic: globally warmed tomatoes still going in November despite our first frost. But they are quite sheltered.
Don't want to be a stubborn denier about this, but I'm not buying it.
ECS could most certainly be 3C. It could even be higher, though I doubt it.
What I'm not buying is that we have moved any closer to knowing what the likely range is.
That may be because my own best guess places ECS at about 2C. But it may also be because we have all been watching the sausage being made for the last decade and it has not inspired confidence.
TBH I haven't looked at the evidence for the decreased range, so I have no strong opinion. But then again, I have no personal reason to doubt them.
Well, this is the third consecutive report where the lower bound of ECS has been changed by half a degree C. It's like a yo-yo. Given the reports on CMIP-6 model behavior, I am happy to let the dust settle for a while before accepting (or completely rejecting) these new estimates.
I don't claim to have read the details, but PFs Twit I found this from claims "Uncertainty halved in both Equilibrium Climate Sensitivity and temperature projections thanks to remote sensing of clouds".
from the AR6
Page not found.
As the relationship between warming and cost isn't linear (twice as much warming is far more than twice as expensive), not "knowing what the likely range is" means we should plan for a larger warming. And hope to get a smaller one.
Odd. Thanks for noticing. I swear I cut-n-pasted it at the time. Now fixed, to yours.
Tom - would it not be strange if the range of ECS hadn't narrowed after 30 years of study and a huge amount of new data? I'm not knocking your scepticism willfully - or at all, in fact - but aren't we at the point where we can say 'About 3' (which JA and WMC have mooted once or twice in the last 15 years..) and move on? Because there are other, more fruitful conversations to be had?
Maybe I'm being unreasonable--I'm willing to consider that. But given that the IPCC said that sensitivity is the most important question to resolve, and given further that observational studies consistently (though not always) come in with much lower estimates and finally given that the impacts of 2C are probably dramatically different than those associated with 3C, I'm inclined to hold out on my POV.
If your memory (and reading history) goes back far enough, you may recall that I proposed positing 2.5C as a rough estimate of ECS for planning purposes, even though I felt it to be 2C. I was hoping that enough agreement could be reached on the higher figure to deliver something sane for planners and policy makers to work with. I had spoken with a city planner who was trying to create policy guidance around sea level rise and people were telling him he had to plan for between 1 and 3 meters sea level rise this century, which isn't reasonable even at 3C, and certainly not at 2C.
Alas, my motion more or less failed for want of a second...
2C is a realistic number to be used in planning...as long as you use the 5C for the other end of the range in planning.
"The equilibrium climate sensitivity is an important quantity used to estimate how the climate responds to radiative forcing. Based on multiple lines of evidence, 21 the very likely range of equilibrium climate sensitivity is between 2°C (high confidence) and 5°C (medium confidence)."
Yeah, Phil, I honestly don't see 5C is at all realistic. I read the IPCC and a couple of dozen papers a year, but I'm no expert. I'll admit that at the start. What I do see leads me to my lukewarmerish point of view. 3C? Well, maybe. 3.5C? If nobody on the planet is making good observations over the past quarter of a century, than.... maybe. But more than that? I don't see it.
Again, not an expert, but obviously I'm hoping I'm right.
3C is likely.
Don't forget that the warming we see is slowed by the thermal inertia of the oceans.
For many years, climate scientists have been criticised for not narrowing the ECS range (for a long time, it has been very similar to what was presented in the Charney report from 1979). Now that it's been narrowed, Tom isn't buying it. Oh well.
There seem to be two main factors:
1) New bottom-up cloud process observations suggesting little prospect of a net-negative cloud feedback. Given no-feedback + water vapor gets to a little under 2.5C the total net feedback is then likely to be > 2.5C.
2) Substantially more negative central and upper-bound aerosol forcing estimate compared with AR5.
Tom appears to have missed recent science which raised ECS estimates from observations, considerably. No surprise that better agreement among methods tightens the range.
ATTP, I was not one of those making 'those criticisms.' I make other criticisms instead. I do think that the range of potential figures for ECS lessens the utility of projections. I have been known to remark that both Al Gore and James Inhofe could use ECS estimates that fall within IPCC ranges to justify their political positions. That's actually still the case.
Chubb, I have read some revisions to ECS estimates, both lowering the high end and raising the low. My reaction after having read them is to hope there are more studies in the works that perhaps provide better data.
The current range of ECS estimates offered by the IPCC is still too large to benefit planners and policy makers, especially given that the current range still comes with significant uncertainty attached. One side of the conversation wants to focus on the high end, the other side looks at the low. Conflict ensues.
My bottom line on ECS is that we still don't know what it is within one degree, and people who say they do (my personal best guess is based on hope as much as quite a bit of reading) are kidding themselves and others they're talking to.
Tom - I get it, you want/expect a precise number at the low end of AR5. Unfortunately that isn't available.
There are always measurement tolerances. Fact of life.
Picking a single number "that falls in the range" is a way of making a something that doesn't "work first time every time all the time". If you get on an airplane, do you want it designed by picking a single number that "falls in the range"?
A realistic design/plan uses the whole range.
It has been clear to anyone that bothered to look carefully since at least the 1970's that a significant risk existed. The range of risk has narrowed. That's actually a good thing.
But appropriate action more or less depends on having good information. If ECS is low, we have more time to act and it will be less expensive. If ECS is high we must act more quickly and rush technology adoption that is as a result much more expensive.
At COP26 there are leaders of island nations demanding guaranteed immigration to other countries if their islands sink beneath the waves. But the surface of their islands is actually increasing. I think we should grant them conditional immigration if their islands go under. But I think we're wasting valuable time and money discussing something that isn't happening now and is unlikely to happen in the future--if my guess/hope/belief/and some analysis of ECS is correct.
The island nations are so tiny that fixing them by immigration would be trivial; if they were GW's biggest problem, or even in the top 10, then we'd be much much better off than we actually are. But that's not the point of their complaints; the point is theatre, so fixing is not the aim. Though I suspect they wouldn't object to more money.
If the thrust of the jet was better known, we might take off safely with more cargo on the plane. But we have the knowledge we have, and that doesn't often change fast. We must make decisions based on what facts we know.
Guessing, hoping and belief do not make for a safe flight. An example:
Far too many people live in fantasy lands, and don't want facts.
Fact is that improving the range estimate for the ECS isn't easy. Smart people have tried, and have indeed reduced the range... but not much.
But Phil--and I'm not trying to start a fight here--isn't it the activist side that's doing the guessing?
As a lukewarmer, I have no problem with the greenhouse gas theory, its implications for future warming, the potential impacts of that warming on infrastructure and society. Real, potentially dangerous, worth addressing. Much of that has been known since President Johnson was briefed on it in 1965.
But our lack of knowledge about ECS handcuffs us on choosing right action, prioritizing our efforts and assisting those with fewer resources.
If ECS is around 2C (as I am guessing), than the impacts of our contributions to climate change are well within current capabilities (and budgets) to address. If it is around 4.5C (which I believe is no longer considered a serious possibility) than it is like mobilizing for World War III.
How can any politician operate with such uncertainty? We can tell them 'hope for the best, prepare for the worst,' but the implications for that are stark--energy poverty in the developed world, continued economic immiseration for the developing world, etc., etc.
We need to have a narrower range of ECS that has a more solid foundation behind it.
> isn't it the activist side that's doing the guessing?... If ECS is around 2C (as I am guessing)
It looks like it is you that is doing the guessing. Unless you have specialist knowledge, why do you think your guess is better than the IPCC best-guess? See-also https://wmconnolley.wordpress.com/2016/12/07/scott-adams-is-a-tosser/
I am guessing. That's why I said 'my guess.' I don't think my guess is better than the IPCC's. Sadly, I see nothing that tells me that their guess is any better than mine. CMIP 6 is kind of a fiasco--it seems as though model output is getting worse, not better. The temperature record leans more in my favour than theirs (at the moment and depending how long you look and how hard you squint sometimes).
Am I getting this completely wrong? I'm open to the possibility. But what I've seen doesn't lead me directly to that conclusion.
> Sadly, I see nothing that tells me that their guess is any better than mine
That's an odd thing to say. Try reading https://wmconnolley.wordpress.com/2016/12/07/scott-adams-is-a-tosser/ more carefully. You really think you have expertise to match the IPCC? I know I don't.
> CMIP 6 is kind of a fiasco... Am I getting this completely wrong?
Yes. You're over-weighting CMIP6.
I didn't read your 'adams is a tosser' post before, as I already knew he is a tosser, albeit a wicked funny one a lot of the time.
Regarding your post, you make some good points, but some of them are worth discussing.
Of course we non-scientists are forced to rely on authoritative voices we trust. But you refer to a 'consensus,' one which has been falsely presented to us.
Let me be clear--I am convinced that a majority (66%) of climate scientists believe in what I call a narrow view of the conventional presentation of human contributions to a changing climate. Specifically, that half or more of current warming. Repeated surveys of working climate scientists come up with that percentage.
And I agree with them, not that they were asking for my agreement.
But what is presented to us is propaganda--that '97% (now 99%) of scientists agree that humans are causing all changes to the climate. And the work that they cite by people like Cook and Lewandowski is available for examination and I do have subject matter expertise in what they did to arrive at those conclusions. (I also am competent to evaluate the real surveys conducted by Verheggen et al, Storch, Bray et al, and others.)
And what Cook and Lewandowski (with the participation of people like ATTP, who really should have known better) came up with is garbage. And I know that it's garbage.
So when you write "It is not sensible to conclude that the scientific consensus, as shown by that authority, is wrong7" I don't disagree with your point. What I dispute is the widely available description of that consensus.
Two-thirds of scientists is a robust consensus that should inform policy makers and the public perception on this issue. But it ain't 97% and phoney claims interfere with sound discussion.
When the minority includes people like Lindzen, the late Freeman Dyson and other luminaries, the minority view needs to be taken seriously. It does not mean the minority is right--but they need to be listened to.
Back in a more contentious era, you and I fought over your calling Curry a bozo. But she's a climate scientist. When I call Cook a bozo, I'm labeling a cartoonist.
Ah, well. End of rant. Peace be unto all.
Whoops--I accidentally deleted half a sentence.
What I intended to write was "Let me be clear--I am convinced that a majority (66%) of climate scientists believe in what I call a narrow view of the conventional presentation of human contributions to a changing climate. Specifically, that half or more of current warming is caused by human activity and that the primary activity is our emission of greenhouse gases.'
You appear to be completely confused, so much so that I hardly know where to start. C+L are totally irrelevant and I have no idea why you are referring to them. By "consensus" I mean the IPCC.
FD has no expertise and is anyway stiff. L is emeritus (and has been for more than a decade; refer to http://mustelid.blogspot.com/2005/11/sht-frm-lindzen.html). Curry was never better than a mid-ranker, and she is now retired (see-also https://wmconnolley.wordpress.com/2016/11/14/judith-curry-wtf/). You are relying on very poor support. And, per adams-is-a-tosser, you should not be. Your expertise does not supersede the IPCC's, but it should be enough to allow you to recognise the IPCC as the authority you defer to. Clutching at C+L as strawmen to oppose is weird.
As an aside, "half... of current warming is caused by human activity" is also wrong / misphrased: the actual answer is "more than 100%". I'd have expected you to know that.
Hiya WMC--no interest in fighting with anyone anymore. That phrasing comes from Verheggen et al 2013 and echoes the phrasing in Bray, von Storch et al 2010. That's what the consensus actually signs up for, or at least that's what 66% of working and published climate scientists agree to.
I respect the IPCC, WG1 at least. No quarrels with them. But the 'consensus' as it is portrayed in the media, at COP26 and here in the blessed blogosphere is quite different. Specifically, the consensus has been misrepresented by Cook, Lewandowski, Oreskes and others who say really wrong things about it.
I have read quite frequently that more than 100% of current warming is caused by human activity. Bart V used to write about it a lot on his blog. And if ECS is over 3C you can make a case for it. Otherwise, no.
Freeman Dyson worked in climate science for 15 years. I'm curious as to why you say he has no expertise.
Yep Lindzen and Curry have retired. So has James Hansen. Are we free to ignore what he has written over the decades because he has now retired?
FD: news to me. Ref one of his papers
Last time I discussed Freeman Dyson with... who was it? dhogaza? Sod?... they asked the same question. I think he might have co-authored one paper while working with Alvin Weinberg at the Institute for Energy Analysis.
I don't care. When one of the century's finest minds spends 15 years working (part time, assuredly) on climate science, I will listen to what he has to say. I'm not saying he's right. Hell, he said he wasn't sure he was right. But I will listen to him.
And you can, too! https://www.youtube.com/watch?v=8xFLjUt2leM
If he didn't write anything down despite 15 years of work he wasted his time.
But not ours.
Generalised surveys like that are problematic. Basically there are only a tiny minority of mainstream climate scientists who actually address the human-caused attribution question in any way. Conversely pretty much 100% of contrarian scientists like to address this question frequently.
In the Verheggen et al. survey 15-20% of respondents did not provide a quantitative answer to the attribution question, instead answering "unknown", "don't know" or "other. Verheggen et al. also asked a qualitative question: whether GHGs had caused "strong warming", "moderate warming", "slight warming" etc. The vast majority of those who did answer that but gave a non-quantitative answer to the other were in "strong" or "moderate" warming categories. Figure S7 in that paper shows that if you remove non-quantitative answers those with the highest level of expertise (as determined by number of climate papers) are at about 90-95% consensus on >50% contribution.
But it also appears that most of the survey respondents didn't fully understand the question and/or the IPCC attribution statement. You've stated that Verheggen et al. asked about percentage human contribution but the paper says they specifically asked about GHG contribution. The consensus on that is unquestionably >100% given negative aerosol forcing, but instead 76-100% was the most popular response.
There's also an odd result that respondents tended to say that land-use is a fairly important warming factor whereas AR4 found a negative forcing from land-use (albeit there may be localised surface warming due to some land-use changes). Difficult to know what they were thinking, but I would suggest most likely it was CO2 emissions due to deforestation, which aren't counted like that in attribution. Again indicating that many respondents didn't fully understand the issues or questions.
Addendum: The paper also shows likelihood of answering >100% contribution correlates strongly with expertise, though even the highest expertise grouping answered 76-100% with slightly greater frequency.
"How can any politician operate with such uncertainty? We can tell them 'hope for the best, prepare for the worst,' but the implications for that are stark--energy poverty in the developed world, continued economic immiseration for the developing world, etc., etc."
Embrace uncertainty. A fact of life.
Far better to be uncertain than to be certain and wrong.
Then I feel much better. I am uncertain.
There were differences in phrasing on attribution between Verheggen et al and Bray, von Storch et al. I might have elided the two. I don't believe that that undercuts my main point, which is that climate scientists are more cautious and have a narrower view of what we know about the Current Warming Period than people from lobbies, NGOs, etc. who pronounce upon our current predicament.
Don't get me wrong on this. The majority of climate scientists believe that human caused warming is real, serious and they agree with IPCC WG1. There is a consensus. It just isn't the consensus that is painted by people like Cook, Oreskes and Lew.
You mean not the consensus of the the IPCC report. You don't agree with the IPCC, or you would be talking about what policies made sense across the range of possible warmings.
Yawn. I can take a nap while you work on it.
Have a nice nap, Phil.
The IPCC has three working groups. I agree with WG1. When the IPCC published its report in 2014 on the projected impacts of warming through 2100, it was studiously ignored as it wasn't disastrous enough. Since then, WG2 and WG3 have gone to great lengths to ignore it.
The IPCC WG1 central estimate of ECS is 3 oC. It is good to know that you agree with that.
Embrace uncertainty. A fact of life.
The thing about climate science is that uncertainties are front-and-centre and clearly quantified... so people talk about uncertainties as a problem. The reality is that the uncertainties are smaller than is the case for most things politicians deal with, but in those cases uncertainties tend to go unquantified and unstated so people just assume they don't exist until the outcome doesn't match expectations.
It's one thing I've come across with energy scenario peeps and the #RCP85isbollox stuff. RCP8.5 is a product of uncertainty in future techno-socio-economic outcomes. Every analysis I've seen being used to conclude #RCP85isbollox has assumed zero uncertainty in techno-socio-economic outcome, meaning they aren't suitable for assessing likelihood of reaching that level of forcing by 2100. I've tried to explain this many times but they don't seem to get it.
There just seems to be a culture in the energy analysis field of not quantifying uncertainties, perhaps ultimately out of recognition that uncertainties are so large and unknowable that we can't sensibly quantify them. Yet perversely their projections are routinely treated as equivalent to observations because they don't specify uncertainty.
WMC: Yes, the central point in their range is 3C. But the range is too wide to be useful.
Paul, you make a very good point. However, RCP 8.5 is still bollox. And just because politicians don't act or think like scientists doesn't mean scientists shouldn't.
There were differences in phrasing on attribution between Verheggen et al and Bray, von Storch et al. I might have elided the two
My point wasn't about you getting it wrong. It was that there are some niche terminological specifics regarding the IPCC attribution statement which have caused widespread confusion among people not well-versed in those specifics. And those misunderstandings would tend to cause a low bias in perceived consensus endorsement given the nature of these surveys.
Specifically, there are two main causes of confusion:
1) Difference between human total net contribution and GHG-only contribution
2) That it's not at all problematic for human/GHG contribution to be substantially greater than 100%
Verheggen et al. specifically asked about the GHG-only contribution. IPCC AR5 stated a 0.5 - 1.3C contribution from GHGs between 1951-2010, relative to 0.65C observed warming. You've indicated a belief that the majority of climate scientists would endorse this IPCC statement.
These facts being the case, you should expect >100% to be the answer with the highest frequency, but it isn't. Not even close. Highest is 76-100%, with >100% roughly equal with 51-75%, which actually lies outside the IPCC stated range.
Why? Well, I think there's a possible survey design issue. Setting >100% as the highest option makes it look like an extreme answer, when it's really the correct answer. I wonder what difference it would have made to have >150% and >200% options. But that's really part of the issue that probably a high proportion of respondents didn't properly understand the question and/or didn't fully understand the IPCC attribution statement.
Also, keep in mind that there's been another 0.3-0.4C warming since those surveys
happened. I would be pretty confident at this point that the percentage of active climate scientists who endorse the IPCC statement, having fully understood the statement and the question about it, would be 99%+.
Regarding your last point, that was what people were arguing in advance of Verheggen--that time had passed and temperatures climbed since Bray, von Storch and that more scientists would have climbed on board. Didn't happen.
I don't think that more than 100% is the correct answer. More importantly, I don't think the data is there to show you or I to be correct or incorrect.
In the same way that I think "About 3" is a good (and good enough) answer to the ECS question, I also think that "About 100%" is a good (and good enough) answer to the attribution question. In both cases I would add "Thanks climate scientists, we can take it from here, but do continue your studies and get back to us if anything changes"
that time had passed and temperatures climbed since Bray, von Storch and that more scientists would have climbed on board. Didn't happen.
I don't know if the Verheggen paper did or didn't find a greater level of endorsement after accounting for differences between the surveys, but the Verheggen survey happened right at the end of "the hiatus" so there hadn't been much apparent surface warming since the von Storch survey.
I don't think that more than 100% is the correct answer. More importantly, I don't think the data is there to show you or I to be correct or incorrect.
The data is clear that anthropogenic aerosols have most likely caused a substantial negative forcing to build up since pre-industrial and since 1950.
We have clear data that solar forcing since 1950 is neutral to slightly negative. We have good data on volcanic forcing that the forced response since 1950 is neutral to slightly positive. Overall most likely natural forced response is therefore zero.
Internal variability is arguably an unknown (though instrumental and proxy reconstruction data places some probabilistic bounds) but, that being the case, a reasonable best guess answer has to be zero since the chances of being positive or negative are equal.
So, we have observed warming but, in terms of data on known climate influences, so far we only have cooling. The only known influence remaining is from GHGs. And here we have clear data of very substantial increase, comfortably enough to fill the gap to observed warming.
It would take a very convoluted set of stipulations to arrive at any result other than GHGs contributing >100% warming since 1950.
Also, observed warming was about 0.65C between 1951-2010 (the AR5 period). GHG forcing increase was 2 or 2.2W/m2 depending on whether you include Ozone. 0.7C warming (i.e. >100% of observed) would therefore be produced from GHG forcing given a TCR of 1.2 or 1.3C. This is highly consistent with ECS of ~ 2C so logically you actually should believe GHG contribution was > 100%.
Tom: "the central point in their range is 3C. But the range is too wide to be useful."
The range of ECS is useful. It is good enough.
The future is unknown in many ways. Try to forecast interest rates, technological change, market problems such as monopoly, weather events, wars, revolutions, income distribution, population growth, government policy and taxes, and of course all of these are interdependent.
Some things are predictable. One of the known things is that replacing technologies takes time. An example I've talked about here before is electric cars. Another is the historical coal to oil shift.
Past changes show similar patterns.
Electric cars were enabled by technology change, the invention of the Li-ion cell by Whittingham, and early production in the 1970s by Exxon. While the initial cells were not practical, the technology kept improving, and before 2010 practical cars were being made. Since about 2011, production has followed an exponential growth curve of doubling about every 2.5 years. This type of growth is typical for a new technology. If we project this forwards, most of the cars sold in a bit more than another decade will be electric. As the lifetime of cars is about 24 years in the USA (different in other places, of course), in about 40 years most cars on the road will be BEVs. Government policies can shift this by at most a few years earlier.
BEVs are a bright spot, as the "green premium", or the extra cost to reduce CO2 is negative, and will happen with any additional government policy. Other needed changes to get to low CO2 and eventually to zero CO2 are more expensive than fossil fuels at this time, and perhaps will be forever. About the best we might hope for is SSP2-4.5, SSP3-7.0 is about the center case and SSP5-8.5 is about worst case. Based mostly on the past history of technological change and the current state of major part of the economy.
Try to get 1.5 C maximum warming out of an economic system that takes over 40 years to change is, to use the UK term, "bollox". The only way to do this is to drastically reduce fossil fuel use starting about next week, perhaps by a worldwide punitive tax, which would trigger a massive depression. Which would likely trigger a war, revolution, or similar. Likely reversing the tax or whatever was used to drastically reduce fossil fuel use.
Sustainable change requires lots of time. This problem is slow, with a time scale beyond a human lifetime. A delay of a decades matters little. Sure, finding an exactly optimum path to zero CO2 would require an exact answer for the ECS. The other uncertainties make finding an optimum path impossible. The future is uncertain. So not having an exact answer for ECS doesn't matter.
Other uncertainties dominate. We have a good enough answer for ECS now.
> the range is too wide to be useful
> We have a good enough answer for ECS now
Assuming we're talking about "a likely range of 2.5°C to 4°C"...
The range is wide enough to not allow terrible things to be ruled out; and that even the low end requires action. And narrow enough that the best-guess estimate of 3 oC, which everyone in practice uses, isn't too far from each end. So narrowing the range much wouldn't get you much more.
So I think I'm with Phil on this one: as much of the answer as we already have is useful, at least for policy purposes, which are so broad-brush.
Yes, using the likely range or the very likely range of 2°C to 5°C. No real difference between them that I see.
"BEVs are a bright spot, as the "green premium", or the extra cost to reduce CO2 is negative, and will happen with any additional government policy."
When I write for pay, I read it again several days later to find things like this. Sigh. Maybe this makes slightly more sense.
"BEVs are a bright spot, as the "green premium", or the extra cost to reduce CO2 is negative, and will largely happen without any supporting government policy."
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