SciAm's climate sensitivity car crash

Updated on Apr 25, 2015 by Bishop Hill

Updated on Apr 25, 2015 by Bishop Hill

When the climate alarmist is struggling to make his case, he tends to reach for either the ad-hominem argument or some other rhetorical technique from the depths of the propagandist armoury.

Readers will recall the Bjorn Stevens paper on aerosols, which I suggested at the time gave alarmism "one helluva beating", as indeed it does. My headline seemed to amuse others and it was echoed by James Delingpole at Breitbart, his article later reproduced at Fox News.

The inevitable response was a statement by Stevens that sought to calm the troubled waters, suggesting that unidentified parties were claiming that it was the end of the global warming hypothesis. This was a fairly obvious straw man argument, but one that was sufficiently robust for Scientific American, which has now picked up the story in rather embarrassing fashion.

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A declaration of orthodoxy

When a mainstream climate scientist comes up with some findings that go against the narrative of impending catastrophe they usually feel obliged (or are obliged by others) to take steps to distance themselves from the implications - hiding them, issuing declarations of orthodoxy, or saying something rude about dissenters.

We saw something of this in Bjorn Stevens' recent paper on aerosol forcing, with the implications for climate sensitivity left to one side. Yesterday, however, Stevens went futher and issued a declaration of his absolute global warming faith.

Many scientists (myself included) believe that a warming of more than 2ºC from a doubling of the concentration of atmospheric carbon dioxide is consistent with both my new study and our best understanding. Some insight into our reasoning can be found in a number of excellent blogs reporting on a workshop on Earth’s Climate Sensitivities, which I co-organized just last week, e.g., http://www.realclimate.org/index.php/archives/2015/04/reflections-on-ringberg

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Johansen's climate sensitivity estimate

April 1st is an interesting choice of date on which to release a new paper on climate sensitivity, but nevertheless that is the choice of Nature Climate Change. The new estimate has been produced by a team led a new name in this area: Daniel Johansen of Chalmers University of Technology in Gothenburg. The only member of the team who may be familiar to readers is Claudia Tebaldi.

The article's headline conclusion is that ECS cannot be lower than 2°C.

Here we analyse how estimates of ECS change as observations accumulate over time and estimate the contribution of potential causes to the hiatus. We find that including observations over the hiatus reduces the most likely value for ECS from 2.8 °C to 2.5 °C, but that the lower bound of the 90% range remains stable around 2 °C. We also find that the hiatus is primarily attributable to El Niño/Southern Oscillation-related variability and reduced solar forcing.

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Ringberg

Climate sensitivity experts from around the world are spending the next week at a castle in Germany. The Ringberg conference features a stellar cast of speakers who will look at the latest developments in the area.

For readers who are on Twitter, highlights of the discussions can be seen on the Ringberg15 hashtag. Some BH regulars will be interested in one of the first tweets, from Gavin Schmidt:

Knutti and Gregory giving lots of examples of how simple assumptions in forcing/feedback paradigm break down.

The IPCC versus Stevens

I've updated Nic Lewis's graph of his new climate sensitivity estimates by adding the IPCC's likely range of 1.5°C–4.5°C as a grey box. Something of a contrast here I would say.

The situation for TCR is only marginally better.

Update on Mar 20, 2015 by Bishop Hill

In the comments at CA, Shub and Nic Lewis point to another important implication of the Stevens paper:

SHUB: Do low estimates for aerosol cooling imply the 1940-1978 drop in global temperatures were not due to coal plant emissions from post-war industrialization?

LEWIS: Yes, they strongly suggest that the main reason for global temperature going down rather than up from 1940 to the mid-1970s despite quite strong greenhouse gas forcing (+0.7 W/m2 for long-lived GHG, +0.85 W/m2 including ozone) lay elsewhere. Internal variability (here the AMO) seems the obvious cause. On Steven’s best estimates, aerosol forcing became a bit under -0.3 W/m2 more negative during this period. Sulphate emissions from coal plants etc. grew rapidly and reached their peak level in the mid/late 1970s.

Climate sensitivity takes another tumble

Over at Climate Audit, Nic Lewis reports on the publication of a very important paper in Journal of Climate.

Bjorn Stevens has created a new estimate of the cooling effects of pollution ("aerosols") on the climate. Readers will no doubt recall that to the extent that aerosol cooling is small the warming effect of carbon dioxide must also be small so that the two cancel out to match the observed temperature record. Only if aerosol cooling is large can the effect of carbon dioxide be large.

Stevens' results suggest that the aerosol effect is even lower than the IPCC's best estimates in AR5, which were themselves much lower than the numbers that were coming out of the climate models. He also suggests that the number is less uncertain than previously thought. This is therefore pretty important stuff. 

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Marotzke's mischief

Readers may recall Jochem Marotzke as the IPCC bigwig who promised that the IPCC would not duck the question of the hiatus in surface temperature rises and then promptly ensured that it did no such thing.

Yesterday, Marotzke and Piers Forster came up with a new paper that seeks to explain away the pause entirely, putting it all down to natural variability. There is a nice layman's explanation at Carbon Brief.

For each 15-year period, the authors compared the temperature change we've seen in the real world with what the climate models suggest should have happened.

Over the 112-year record, the authors find no obvious pattern in whether real-world temperature trends are closer to the upper end of what model project, or the lower end.

In other words, while the models  aren't capable of capturing all the "wiggles" along the path of rising temperatures, they are slightly too cool just as often as they're slightly too warm.

And because the observed trend over the full instrumental record is roughly the same as the model one we are cordially invited to conclude that there's actually no problem.

If Carbon Brief is reporting this correctly then it's hilariously bad stuff. Everybody knows that the twentieth century is hindcast roughly correctly because the models are "tuned", usually via the aerosol forcing. So fast-warming/big aerosol cooling models hindcast correctly and so do slow-warming/small aerosol cooling models. The problem is that the trick of fudging the aerosol data so as to give a correct hindcast can't be applied to forecasts. Reality will be what reality will be. The fact is we have models with a wide range of TCRs and they have all been fudged. Some might turn out to be roughly correct. But it it just as possible that they are all wrong. Given the experience with out of sample verification and the output of energy budget studies, it may well be that it is more likely than not that they are all wrong.

Boxed in - Josh 307

Sans science, sans maths, sans everything.

Cartoons by Josh

Sans science, sans maths, sans everything

Updated on Jan 13, 2015 by Bishop Hill

Updated on Jan 13, 2015 by Bishop Hill

Over at Lucia's place, there has been some interesting conversation in the comments about the technical abilities of some of those on the other side of the climate debate. This originally arose in connection the host of And Then There's Physics, who had apparently reduced Blackboard regular Paul K to laughter in a post about a paper on climate sensitivity by Craig Loehle and a response to it, Cawley et al, which was written by five of the denizens of Skeptical Science. This amusement was followed by others chipping in with their own surprise at ATTP's comments. It's all good family fun. However, it turns out that it's not only ATTP who is struggling. Nic Lewis has added a comment to the thread about the Cawley paper itself which is astonishing.

First a bit of background. Loehle's paper described a model developed in an earlier paper (Loehle and Scafetta 2011) and used it to derive an anthropogenic warming trend from the mid-20th century onwards. The paper then derived an estimate of transient climate response (TCR) of 1.1°C by relating the anthropogenic trend rise in temperature to the increase in anthropogenic radiative forcing, and went on to derive an estimate of equilibrium climate sensitivity (ECS) of 2.0°C. The Skeptical Science response appeared about six months later and was written by Gavin Cawley, Kevin Cowtan, Robert Way, Peter Jacobs and Ari Jokimäki. This is the key part of the abstract.

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Schwartz on climate sensitivity

Stephen Schwartz et al have published a paper in a journal called Earth's Future that reviews and considers the recent low estimates of climate sensitivity, wondering what the divergence of the different estimates might mean:

Earth's equilibrium climate sensitivity (ECS) and forcing of Earth's climate system over the industrial era have been re-examined in two new assessments: the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), and a study by A. Otto and others (Nature Geosci., 2013). The ranges of these quantities given in these assessments and also in the Fourth (2007) IPCC Assessment are analyzed here within the framework of a planetary energy balance model, taking into account the observed increase in global mean surface temperature over the instrumental record together with best estimates of the rate of increase of planetary heat content. This analysis shows systematic differences among the several assessments and apparent inconsistencies within individual assessments. Importantly, the likely range of ECS to doubled CO₂ given in AR5, 1.5 to 4.5 K/(3.7 W m^-2) exceeds the range inferred from the assessed likely range of forcing, 1.2 to 2.9 K/(3.7 W m⁻²), where 3.7 W m⁻² denotes the forcing for doubled CO₂. Such differences underscore the need to identify their causes and reduce the underlying uncertainties. Explanations might involve underestimated negative aerosol forcing, overestimated total forcing, overestimated climate sensitivity, poorly constrained ocean heating, limitations of the energy balance model, or a combination of effects.

Summary: Recent assessments of Earth's climate sensitivity and forcings over the industrial period, taking into account the observed increase in global mean surface temperature and rate of increase of planetary heat content, exhibit differences and apparent inconsistencies.

Ridley's response to Lynas

This is a guest post by Matt Ridley and is a response to this post by Mark Lynas.

As far as I know Mark Lynas is an honourable man. He changed his mind on the benefits of genetically modified crops, going against the views of nearly all environmental campaign groups and bravely putting up with much criticism for doing so. I know how he feels, because I have done the same – changing my mind about the dangers of climate change, going against the views of nearly all environmental campaign groups and putting up with much criticism for doing so.

That Mark does not agree with my change of mind on climate (which happened gradually but was cemented by the way the green and scientific establishments reacted to the Climategate controversy) is fair enough. I don’t, however, understand why he chooses to take the low road in his attacks on me. His latest blog post is entitled “On Matt Ridley’s latest attempt at climate change denial”. He knows full well that I have never advocated climate change “denial” and that that very phrase was invented as a way smear sceptics who think the dangers of climate change are being exaggerated by associating them with holocaust denial. Yuk.

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All together now - Josh 299

Another day and another metaphor, this time from Roger Harrabin on BBC Radio 4 about climate debaters now 'all singing from the same hymnbook' - see yesterday's post below.

It sounded like Roger thought sceptics were now changing their tune but clearly, with lower sensitivity, The Pause and no hope of any global policy harmony on the horizon, the strains that are coming from the alarmist camp now have much more of a sceptic air.

Cartoons by Josh

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Sceptics on Radio 4

I gather that there was a segment on Radio 4 about climate sceptics this morning, with an interview with Nic Lewis. I'm going out shortly so I can't record it for you, but you should be able to listen again here in a few hours' time.

Update on Nov 1, 2014 by Bishop Hill

Nic Lewis emails:

As you know, Roger Harrabin's piece on global warming that included excerpts of his interview with me aired at 7.15 this morning on Radio 4.

Unfortunately, his piece confusingly muddled up both CO₂ emissions with CO₂ concentrations and equilibrium climate sensitivity with the transient climate response level. Both equilibrium climate sensitivity and the transient climate response relate to a doubling of atmospheric CO₂ concentration, but the equilibrium sensitivity is higher because the transient response refers to the global warming that occurs over decades rather than the centuries it takes for the ocean to fully warm up and equilibrium to be reached.

Harrabin said "if we double CO₂ emissions - which we are likely to do later this century - we are likely to provoke a temperature rise of about 1.7°C", or similar words. What I had told him was that, based on instrumental observations, I estimated the equilibrium climate sensitivity to be 1.7°C warming for a doubling of CO₂ concentration.

Diary dates, feedback edition

The Royal Society is to hold a meeting on climate feedbacks at the start of December:

The response of Earth’s climate system to a perturbation depends on the sign and strength of several feedback processes. This meeting will present critical assessments of major feedbacks, including those (such as ice sheets and the carbon cycle) operating over long timescales. For each, their role in past and present climate change, and their expected future effects will be discussed.

Details here, including a detailed programme.

RealClimate on Lewis and Curry

RealClimate has emerged from its latest bout of torpor to publish an article commenting on the recent Lewis and Curry climate sensitivity paper. It's written by Richard Millar, one of Myles Allen's post-docs, and the author seems to have adopted a much more businesslike tone than is normal at RC. Unfortunately, according to the first comment, which comes from Lewis himself, he hasn't got his facts right.

Richard Millar, you write

“They use the latest IPCC numbers for radiative forcing and global temperature changes, but not the latest IPCC ocean heat content data”.

The statement that Lewis and Curry (2014) does not use the latest IPCC ocean heat content data is simply untrue.

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