Friday, March 29, 2013

Economist in making sense shocker

Via Stoat, I find the Economist has been saying stuff about climate sensitivity. Somewhat to my surprise given my recent experience of the media, it seems to make a lot of sense. That could just be because it says
"Work by Julia Hargreaves of the Research Institute for Global Change in Yokohama, which was published in 2012, suggests a 90% chance of the actual change being in the range of 0.5-4.0°C, with a mean of 2.3°C"
which is referring to this, but the rest of the article seems mostly pretty good too. I do wonder about: "Nic Lewis, an independent climate scientist, got an even lower range in a study accepted for publication: 1.0-3.0°C, with a mean of 1.6°C." I've not heard anything from him for some time, and I wasn't convinced last time. But the overall message of a lowering probability of a high sensitivity is hard to deny. Unless you are Reto Knutti, that is, in which case "my personal view is that the overall assessment hasn’t changed much". Of course he was only speaking personally there, and what matters in his role as IPCC lead author, is what the (credible) literature actually says.


Magnus said...

How might this afect?

BBD said...

From the Economist article:

Nic Lewis, an independent climate scientist, got an even lower range in a study accepted for publication: 1.0-3.0°C, with a mean of 1.6°C.

I thought NL was a 'semi-retired financier' or something similar. Nor did I know that his blog post at Bishop Hill had been accepted for publication. If this is correct, it will be interesting to see what the reviewers make of NL's submission.

David Young said...

Let me review some information about the peer review process, just to make sure we are clear on this. As James explained on another thread, editors are the final judge of whether to publish a paper. They enlist anonymous referees who are knowledgable in the field to give him expert advice. The whole process is secret and confidential.

So, BBD, if the paper has been accepted, the journal editor has judged it a valuable contribution. That does not imply he agrees with its conclusions. The editor if he is ethical will not care whether Nic Lewis is a "climate scientist," a retired financier, or even a mathematician, engineer, or statistician. The sole criteria should be technical merit.

The reviews (referee reports) will never be seen by outsiders such as yourself. That's part of the way science guards against political pressure by activists to arrive at "correct" conclusions.

Now the process is sometimes compromised by participants in the process such as revealed by the Climategate emails where great care was taken to ensure that "incorrect" results were not published, editors were threatened and and in one case, an attempt was made to get an academic editor fired. I know of no other instance of this kind of intimidation being deployed by the so-called "leaders" of any other field. Usually, it originates with peripheral players trying to make a splash or activists trying to influence the process for political or monetary reasons.

Further, I have seen no believable rebuttal of Nic's calculations. I would be eager to see a meaningful critique, so I can get a better feel for how robust it is. The objection about aerosol forcing being assumed to be too low on a previous thread I don't think changes the result that much according to Nic. But there are probably other problems that need to be discussed. But its way too early to judge it definitively.

The one fact that stands out here is that the estimates have been going down recently because of a number of factors.

James Annan said...


My gut instinct is, "not a lot". Don't forget, it's been widely asserted that the models mix too much heat into the deep ocean. Therefore I reckon the most reasonable interpretation of this research would be "the models aren't that bad after all", not "o noes it's all much worse than we thought".

I suppose it should in principle nudge up observationally-based sensitivity estimates a touch, but it doesn't alter the fact that the GCMs overestimate the recent surface warming.

Of course, proper calculations will trump my gut instinct...

BBD said...

The sole criteria should be technical merit.

Yes. And there are issues with NL's guest post at Bishop Hill which I would expect conscientious reviewers to examine in detail.

Does anyone actually know *which journal* is supposed to have accepted NL's submission?

David Young said...

I keep hearing about vague and nonspecific "issues" with Nic's calculation from people who fervently hope its wrong for political reasons. I've seen nothing conclusive either here or at Real Climate, which has been in the past very aggressive in attacking those who challenge the "Team" in very harsh and slanderous terms.

BBD said...

David Young

I keep hearing about vague and nonspecific "issues" with Nic's calculation from people who fervently hope its wrong for political reasons.

Ha. I would be delighted indeed if NL's estimate turned out to be correct but my understanding (much enhanced at this very blog) is that it is likely to be biased low.

There is a very great deal of noise being made by people who fervently hope NL is correct for political reasons. And based on your remarks to me elsewhere, it is clear that you are one of them.

David Young said...

So, what are the issues? The only thing I saw here was the contention that aerosol forcing was higher than Nic assumed. I personally don't know the answer and doubt it is knowable with any precision. It's clear the IPCC has been giving people a story that's too alarmist, which is the really important outcome of all this, not quibbling over exact numbers.

I am not an activist and am merely hopeful that for the sake of mankind that the alarming political talk is wrong, as the track record of such end of the world claims seems to indicate. My main concern in this is that climate science needs reformation. Thus, I take with a grain of salt the received dogmas of the "Team' and their activist second string, the latter being politically motivated and experts at grey literature pseudo science.

BBD said...

I cannot help you if after all that has been written here and elsewhere about NL's estimate you still do not understand why it is probably biased low. That is a perceptual problem of your own, and only you can resolve it.

politically motivated and experts at grey literature pseudo science.

Some would suggest that this could serve as a description of Bishop Hill and Nic Lewis.

David Young said...

If Nic Lewis' article is accepted for publication, it will become increasingly difficult for "some" to characterize it as pseudo-science. I'm not expecting that to stop "some = BBD" from doing so.

BBD said...

Ah, the big if.

Which journal is supposed to have accepted NL's submission?

I'm not expecting that to stop "some = BBD" from doing so.

Let's see *if* it gets published and *what* reaches the final draft, shall we? Wouldn't that be best?

As opposed - for example's sake - to touting a guest post at a contrarian blog around the internet and the media as if it were a published study widely held to be robust.

That sort of thing irritates some people, you know.

David Young said...

BBD, As usual with you this conversation is not productive. You will just have to wait for the real facts and data on Nic's paper and refrain from subtly trying to diss it.

BBD said...

Careful with that stone! We're in a greenhouse.


James Annan said...

A birdie suggested Journal of Climate. But if it's accepted, I don't understand why Nic would be keeping it quiet.

Steve Bloom said...

A (preumably and relatively) low-sensitivity effect intrudes. Just sayin'. It's unique in the record AFAIK.

Unknown said...
This comment has been removed by the author.
PeteB said...

That sounds quite hopeful, and I guess ruling out high sensitivity will have quite a large effect when when considering the economics and the potential damage in the future as I expect the cost is not linear.

One thing that seems quite annoying is different methods seem to give different climate sensitivity estimates - so, apart from the higher sensitivities becoming less likely, I don't get the sense that the probability distribution is really converging.

I tried doing a 'back of envelope' calculation from pre-industrial ignoring everything else except CO2!

S = ΔT [ln(2)/ln(C2/C1)]
s=(temperature increase since pre-industrial + warming in the pipeline (Hansen 2005 suggest 0.6deg C)[ln(2)/ln(finish point CO2 in ppm/ start point CO2 in ppm)]

= (0.85+0.6)[ln(2)/ln(397/280)]
1.45*(0.693 /0.349)
= 2.9

If we are really going to get a climate sensitivity of 2 deg C or below (I know you didn't say that!) it would seem that there would have to be quite small aerosol effects, some quite large other anthropogenic forcings, and/or some quite large natural forcings (which seems a bit unlikely, if I understand correctly, we are in a long term natural cooling phase)

James Annan said...

Pete, one trick you are missing there is that the 0.6C "in the pipeline" (which is only an estimate, it's not something we can actually measure directly) is actually conditional on a sensitivity of about 3 (I think). If sensitivity is lower, there is less in the pipeline. So it is somewhat circular reasoning to use that value to argue for a sensitivity of about 3.

Also, yes I understand it is true, that the latest/forthcoming estimate of forcing are indeed that the total forcing is comparable to the CO2-only calculation, because additional positive forcings (including black carbon) are larger, and negatives (aerosol) are smaller, than previously thought. However, this is based on leaked drafts of the IPCC report, which are subject to revision.

Note also that many of the probabilistic estimates cited in the last IPCC report significant probability to S less than 2, even before these recent updates which point to some lowering of estimates.

On the other hand, I don't really disagree with your overall assessment, a sensitivity of less than 2 would be a surprise to me too.

Unknown said...

A more realistic alternative to PeteB's back of the envelope calculation would be using that the current GHG forcing is estimated to be around 3 W/m2. See this blog post by Lennart Bengtsson:

Despite assuming an imbalance of 0.6 K this gives S=1.45/3 = 0.48 K/(W/m2) = 0.48*3.7 = 1.8 K/(2*CO2), less than 2 K/(2*CO2).

Sometimes this is expressed such that the current GHG forcing corresponds to an equivalent CO2 mixing ratio of 490 ppm (also mentioned by Lennart Bengtsson). We then get S=1.45*ln(2)/ln(490/280) = 1.8 K/(2*CO2) as above.