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« Terraforming Mars | Main | Diary dates, fracking edition »
Tuesday
Aug192014

Climate scientists' views on aerosols

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.

Now take a look at climate scientists' views on forcings, and in particular the aerosol forcing. The survey results are split into the opinions of those who think carbon dioxide is responsible for more than half of recent warming and those who think it's responsible for less than half.  Let's call these the big warmers and the lukewarmers. Slightly confusingly the relevant graph shows the lukewarmers in red and the big warmers in blue. Here is is an extract, showing the results for aerosols (click for larger):

If I understand the caption correctly, roughly 19% of lukewarmers offered an opinion on why they think we are not going to fry, at least as regards aerosols. And as you can see, most of those who answered this followup question suggest, with impeccable logic, that the influence of aerosols is slight - the pale red section is long, and much longer than the tiny dark red section. However, the big warmers seem equally inclined to think that the aerosol influence is weak as they do strong. Moreover, very few big warmers seemed inclined to discuss aerosols at all.

How can this be? Don't they understand how central a strong aerosol effect is to their case?

(Caveat: the paper is hard to follow, so it's possible I'm misunderstanding something. It seems to hint at some inconsistencies with scientists' views on aerosols.)

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Reader Comments (24)

Slightly confusingly the relevant graph shows the lukewarmers in red and the big warmers in blue.

Every little rhetorical advantage helps.

Aug 19, 2014 at 11:04 AM | Unregistered Commenteranonym

I think they have given up with logic, science and common sense. They ended up in a situation whereby the models had temperatures roaring away, driven by ever increasing carbon dioxide. The only brake they have to reduce the warming is aerosols, but as others have pointed out, the level of aerosols needed to bring down the warming to observed levels is unrealistic.

They can't bring themselves to admit that their models are wrong or that other natural drivers can affect climate. The science is drifting into fantasy land as they try to avoid admitting that they got it wrong.

Aug 19, 2014 at 11:10 AM | Unregistered CommenterSchrodinger's Cat

Its climate 'science' so heads they win and tails you lose , so they can have both strong aerosol forcing and weak aerosol forcing has 'proof' of AGW
Its one of the many ways this area has a stronger relationship to 'magic' or religion than science as whatever comes up is 'proof' of AGW even if it totally contradicts the claims being made. So no problem.

Aug 19, 2014 at 11:13 AM | Unregistered CommenterKnR

I have a suspicion that maybe I'm no longer welcome, but I'll try to make a serious comment. I believe that the figure relates only to the possible warming influence of aerosols (seeding clouds, or black carbon). In other words, the question that the respondents were answering related to the possible role that aerosols could have played in warming.

The uncertainty about aerosols is really to do with their cooling influence (negative radiative forcing). So, these are - I think - two separate issues. Aerosols can both play a role in warming (through cloud seeding and black carbon) and cooling (through reflecting more incoming sunlight). I believe that the goal of the question was to establish the role that aerosols may have played in our warming, rather than establish the significance of aerosols overall.

Aug 19, 2014 at 11:18 AM | Unregistered CommenterAnd Then There's Physics

'I believe', 'I think', and another 'I believe'. Could it be that your dissonance is sourced in the dissonance of climate scientists about aerosols?
===============

Aug 19, 2014 at 11:36 AM | Unregistered Commenterkim

Wagon circling that turns into swirling as their bs goes down the drain.
That Cook is someone a legit scientist would want to participate with in any study speaks volumes. Bad volumes.

Aug 19, 2014 at 12:01 PM | Unregistered Commenterhunter

However, the big warmers seem equally inclined to think that the aerosol influence is weak as they do strong. Moreover, very few big warmers seemed inclined to discuss aerosols at all.

How can this be? Don't they understand how central a strong aerosol effect is to their case?


A big CO2 sensitivity and a small aerosol sensitivity can be fudged with 'heat going into deep ocean' or 'natural variability' or, I am sure, many other things that prevent big warmers from getting confused.

Aug 19, 2014 at 12:01 PM | Unregistered CommenterGareth

It seems funny to me that nearly every feedback mechanism in Climate Science is positive whereas nearly every one in nature is negative. (Presumably because of the Laws of Thermodynamics, you cannot get more out of a system than is put in.).

But then Climate Science does not follow science as most know it since models are believed rather than reality.

Aug 19, 2014 at 12:04 PM | Unregistered CommenterJohn Marshall

"Don't they understand how central a strong aerosol effect is to their case?"

No. It took me many years to reach this conclusion because I do try to give people the benefit of the doubt, but it does appear that most of these academics are not very bright (relatively speaking).

Aug 19, 2014 at 12:17 PM | Unregistered CommenterWill Nitschke

it does appear that most of these academics are not very bright (relatively speaking).
Better.

Aug 19, 2014 at 12:54 PM | Registered CommenterMike Jackson

aerosols view on climate scientists - they're so dense

Aug 19, 2014 at 1:03 PM | Unregistered CommenterEternalOptimist

Even the IPCC has begun the climb-down on aerosols, though they continue to insist that large aerosol off-sets of GHG driven warming remain plausible. As we might expect from a politically driven field, the climb-down will be slow and contentious; the most extreme in the field are unlikely to ever accept that catastrophic warming is not plausible, no matter how well aerosol effects and heat accumulation are measured, and no matter how obviously wrong GCM projections become versus reality. Still, there is some movement in the direction of sanity; the GISS models have their equilibrium sensitivity scaled back to ~2.5C per doubling, a very long way from James Hansen's earlier (wild-eyed) claims of near 4.5C per doubling.

If the worst of the proposed 'energy policies' (more accurately, Neo-Malthusian anti-growth policies) are not put in place for a decade or two, there will no longer be enough credibility in the catastrophe scenarios for those destructive policies be adopted. Reality will not ultimately be denied; the rational just have to resist the irrational policies of the green loonies for a bit longer.

Aug 19, 2014 at 1:57 PM | Unregistered CommenterSteve Fitzpatrick

Doublethink is the act of simultaneously accepting two mutually contradictory beliefs as correct.
George Orwell coined the word doublethink in his dystopian novel Nineteen Eighty-Four (1984); doublethink is part of newspeak...the novel explicitly shows people learning Doublethink and newspeak due to peer pressure and a desire to "fit in", or gain status within the Party — to be seen as a loyal Party Member.

http://en.m.wikipedia.org/wiki/Doublethink

Aug 19, 2014 at 2:27 PM | Unregistered CommenterBloke in Central Illinois

"views on" or "viewed as"?

[sorry. someone had to.]

Aug 19, 2014 at 2:57 PM | Unregistered Commentermichael hart

Reluctantly I think I agree with ATTP.

The question as to whether aerosols could cause a negative feedback was not asked. Probably on the same basis as a lawyer works: "Never ask a question to which you don't already know the answer"

Once the negative feedback door is opened and we see that the climate is somewhat self regulating the handwaving looks silly.

Aug 19, 2014 at 3:25 PM | Unregistered Commenterclovis marcus

clovis,


Reluctantly I think I agree with ATTP

Sorry :-)


The question as to whether aerosols could cause a negative feedback was not asked. Probably on the same basis as a lawyer works: "Never ask a question to which you don't already know the answer"

Not that I'm particularly interested in defending this survey, but I think there is some logic to the question they asked. We know that aerosols can produce a negative forcing, but it's uncertain and it is indeed one of the big uncertainties at the moment (maybe, more correctly, we know that aerosols can reflect incoming sunlight and, hence, that aspect of their influence would produce cooling). However, what's of long-term interest is how we warm in response to a change in radiative forcing due to GHGs. So, if it turns out that some of our warming is due to a short-term influence from aerosols, that could imply that we're over-estimating the influence of GHGs. Hence the question. Anyway, that's my understanding of the motivation behind the question, FWIW.

Aug 19, 2014 at 4:56 PM | Unregistered CommenterAnd Then There's Physics

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.

Perhaps it will be established that the "climate sensitivity" is itself a variable identity, allowing (sarcastically speaking) for it to be high when needed, and low when needed, at any climate period due to any number of possible explanations.

Consider the 'dendro' sensitivity to temperature also being seen as a variable quantity -- in attempts to explain away the 'decline' in tree-ring proxy temperatures since 1960 or so on the trees that had been showing both recent warming and relative cooling during the MWP.

Aug 19, 2014 at 5:08 PM | Unregistered CommenterSalamano

If a subject has the word "science" in its title, that is a pretty good indication that it is not science.

A few days ago I linked to the ... et al paper, a survey of opinion among climate scientists.
BH


How encouraging it was to read Science of Doom's view in a discussion thread:

However, no point telling you my opinions. Opinions are not really very useful. I would rather present evidence. That takes time.
Unregistered Commenter Science of Doom

Aug 19, 2014 at 6:03 PM | Registered CommenterMartin A

I take a lot of flak over in discussions from asking why it can't all be measured. That's what scientists do, isn't it? Not cling to a hypothesis and not try to justify it with observations rather than models.

Aug 19, 2014 at 6:13 PM | Unregistered Commenterrhoda

ATTP, your attempt to excuse away the scientific dilemma pointed to in the main post is a total fail. Either you did not read the Verhaggen paper, or you were deliberately disingenuous in your post. Neither possibility speaks well.

Aerosols were among the qualitative climate factors in question 3. All results for all respondents for all question 3 factors are plotted in figure 5. GHG warm, aerosols cool, and the other factors are roughly a wash. The more papers they had published, the more strongly respondents thought GHG warmed and aerosols cooled. Figure 5 puts the direct lie to your "I think/believe" otherwise.
This paper does indeed expose the inconsistency inherent in the Warmunist belief system and imbedded in their models that had to be unrealistically aerosol cooled in order to hind cast reasonably well.

Aug 19, 2014 at 6:15 PM | Unregistered CommenterRud Istvan

Rud,
Sorry, I'm not following what you're saying at all. Just seems to be a bit of a rant about warmunists and people lying and stuff. Maybe you could construct an actual argument, or is that not really possible?

Aug 19, 2014 at 6:29 PM | Unregistered CommenterAnd Then There's Physics

Bish, ATTP and Rud

The wording in the paper could usefully be clearer on what exactly Figure 6 is showing. But from the wording of the question in the survey itself, which applied only if the subject had indicated aerosols were a warming influence, I think on this occasion ATTP is contruing it pretty much correctly. The Aerosol question read:

"You attributed part of the warming to aerosols. Which factors cause the net aerosol effect to be warming?
Absorption by black carbon outweighs reflection by the other aerosol and indirect effects via clouds
Indirect effects via clouds cause warming
Other (please specify)"

BTW, Supplementary Information Figure S13 reveals that the paper's headline conclusion that "Respondents who characterized human influence on climate as insignificant, reported having had the most frequent media coverage regarding their views on climate change." is somewhat misleading. Such respondents were under as fiftieth as numerous as those who assessed the GHG contribution as Strong warming, who overall had about 20x as many incidents of media coverage. And those who estimated the GHG contribution to be in the 51-75% range reported very frequent media contact only about one third as often as those who estimated the GHG contribtion as either >100% or <25%. A case of the excluded middle? Figures S11 and S12, which give detailed information of climate sensitivity estimates, are also quite interesting.

Aug 19, 2014 at 8:59 PM | Unregistered CommenterNic Lewis

Nic,
Cheers, seems we can agree sometimes :-)

Aug 19, 2014 at 9:12 PM | Unregistered CommenterAnd Then There's Physics

"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." I didn't think so. There is a big chunk of responses nearer the lower end of the IPCC range, a la Nic Lewis - about a third. Though the question was not asked, those respondents might be expecting less than 2 degree temperature rise without mitigation.
Also, a very tiny fraction believed in high ECS. That may mean that hardly anyone believes in the really scary temperature rises in the "fat tail". For many of us, the risk of those kind of low-probability but much more drastic effects is more concerning than the effects of the IPCC central estimate. However - they were not asked about their range of estimates, just their most likely guess, which is too bad.

Aug 21, 2014 at 9:50 PM | Unregistered CommenterMikeR

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