What New Scientist wouldn't print

A couple of weeks back, New Scientist published an article trying to up the ante on climate sensitivity. 

One headline-making 2013 study had concluded that the immediate warming that would result froma doubling of CO2 in the atmosphere would be around 1.3°C - significantly less than most previous estimates. But this was before global temperatures shot past 1°C above pre-industrial levels last year, as predicted by New Scientist in July 2015. If the 2013 study was repeated using that value, it would give an estimate for the immediate warming of 1.6°C, says Piers Forster...

It also claimed that Forster and Lewis's 2013 paper had got its estimates of aerosol forcing wrong:

[Other studies] suggested that Forster's team underestimated how much warming has been masked by the cooling effect of other pollutants, such as sulphur aerosols, that we pump out alongside CO2. 

Quite why anyone would want to estimate TCR from a single year's temperature figure is anyone's guess. This observation prompted Nic Lewis to write a letter to the editor, which, needless to say, has not been published. So you can read it here.

Letter to the Editor concerning New Scientist article in the 28 May 2016  issue, Vol 230, No 3075, page 8: 'Earth's sensitive side'

The claim in your 28 May article 'Earth's sensitive side' that the strong warming over the last few years means we can now rule out low estimates of climate sensitivity is wrong. You quote Piers Forster, a co-author (along with myself) of one 2013 study that concluded near-term warming from a doubling of CO₂ in the atmosphere would only be around 1.3°C. I have also been sole or lead author of three different studies published since then, all of which support that conclusion. One of those studies used the Intergovernmental Panel on Climate Change 2014 assessment report's estimates for the effects on the Earth's radiation balance of both warming agents such as CO₂ and of cooling agents such as sulphur aerosols. I have extended these estimates to 2015 and recomputed the warming from a doubling of CO₂. It is unchanged at 1.3 °C, averaging over 1995-2015 data. It remains 1.3 °C when using data just for the last ten, or five, years. Use of a shorter period gives a less reliable estimate; using a single year's temperature is unsound.

The suggestion that the team Forster and I were part of underestimated how much warming had been masked by the cooling effects of sulphur aerosols and other pollutants is mistaken. Our team's method is unaffected by the arguments on this point raised by the Shindell and Schmidt team studies referred to. The latter study anyway contained several errors.  The corrected version fixed two of the errors I had pointed out, and shows that near term warming from a doubling of CO₂ is correctly estimated from the historical mix of warming and cooling agents, including sulphur aerosols. Moreover, the findings by the Storelvmo team relied on a relationship existing between solar radiation at the surface and sulphur emissions, but over their full data period that relationship is statistically insignificant. Furthermore, two recent studies (Stevens 2015 and Kirkby et al. 2016) conclude that sulphur aerosols have had less effect on radiation than previously thought, implying that estimates of the warming from a doubling of CO₂ are actually too high.

How low can ECS go?

A new paper in a journal called Earth and Space Science says that effective climate sensititivity could be as low as 1°C. Here's the abstract.

Estimates of 2xCO2 equilibrium climate sensitivity (EqCS) derive from running global climate models (GCMs) to equilibrium. Estimates of effective climate sensitivity (EfCS) are the corresponding quantities obtained using transient GCM output or observations. The EfCS approach uses an accompanying energy balance model (EBM), the zero-dimensional model (ZDM) being standard. GCM values of EqCS and EfCS vary widely [IPCC range: (1.5, 4.5)°C] and have failed to converge over the past 35 years. Recently, attempts have been made to refine the EfCS approach by using two-zone (tropical/extratropical) EBMs. When applied using satellite radiation data, these give low and tightly-constrained EfCS values, in the neighbourhood of 1°C. These low observational EfCS/two-zone EBM values have been questioned because (a) they disagree with higher observational EfCS/ZDM values, and (b) the EfCS/two-zone EBM values given by GCMs are poorly correlated with the standard GCM sensitivity estimates. The validity of the low observational EfCS/two-zone EBM values is here explored, with focus on the limitations of the observational EfCS/ZDM approach, the disagreement between the GCM and observational radiative responses to surface temperature perturbations in the tropics, and on the modified EfCS values provided by an extended twozone EBM that includes an explicit parameterization of dynamical heat transport. The results support the low observational EfCS/two-zone EBM values, indicating that objections (a) and (b) to these values both need to be reconsidered. It is shown that in the EBM with explicit dynamical heat transport the traditional formulism of climate feedbacks can break down because of lack of additivity.

Predictably, our scientivist friends don't like it, but it's interesting to see that there are still a few hardy souls who are willing to say what they think.

The Bob-bot strikes again

 

At the end of last year, Bob Ward had this to say about a new paper on climate sensitivity:

A new paper on climate sensitivity that @mattwridley and other peddlers of denial will pretend does not exist: https://t.co/RJWJFNODkR

— Bob Ward (@ret_ward) December 31, 2015

In fact, far from being ignored by the sceptic community, the paper in question, by Marvel et al., turned out to be something of a car-crash and was the source of steady stream of more-or-less amused blog posts in the months that followed.

This morning I couldn't help but wonder if someone has replaced Bob with a bot, preprogrammed to issue identical tweets in the response to any new paper on climate sensitivity:

New paper on climate sensitivity that @mattwridley and other climate change 'sceptics' will pretend does not exist: https://t.co/nXqOqxkz3D

— Bob Ward (@ret_ward) April 8, 2016

The paper, by Tan et al., looks as though it's a GCM-with-observational-constraints effort. 

Global climate model (GCM) estimates of the equilibrium global mean surface temperature response to a doubling of atmospheric CO2, measured by the equilibrium climate sensitivity (ECS), range from 2.0° to 4.6°C. Clouds are among the leading causes of this uncertainty. Here we show that the ECS can be up to 1.3°C higher in simulations where mixed-phase clouds consisting of ice crystals and supercooled liquid droplets are constrained by global satellite observations. The higher ECS estimates are directly linked to a weakened cloud-phase feedback arising from a decreased cloud glaciation rate in a warmer climate. We point out the need for realistic representations of the supercooled liquid fraction in mixed-phase clouds in GCMs, given the sensitivity of the ECS to the cloud-phase feedback.

I can't imagine quite how large the gap between a 5.7°C-ECS climate simulation and the historical temperature record is going to be. I wonder what fairy story will be conjured up to explain that away.

Lewis lands a blow

Over at Climate Audit, Nic Lewis has outlined the latest developments in the saga of the Marvel et al paper, which claimed to have demonstrated that climate sensitivity is low, but appeared to have a whole series of problems, not least of which that it had got its forcing data mucked up, leaving out land-use changes entirely.

In a typically erm...robust article at RealClimate, Gavin Schmidt ignored all the evidence Lewis had presented showing that land-use change had been overlooked, and said that Lewis's critique was made...without evidence. However, it now seems that he has decided that this position is not tenable, at the journal at least,and a correction has been issued admitting that land-use was indeed missing.

The historical instantaneous radiative forcing time series was also updated to reflect land use change, which was inadvertently excluded from the forcing originally calculated from ref. 22.

Gavin has thanked Nic Lewis for pointing out the error. Unfortunately, he has chosen to ignore four other problems that Lewis has has pointed out. 

But hey, one out of five ain't bad.

Marvellous exchanges

The latest exchanges over the Marvel et al paper make for fascinating reading. Over at RealClimate, Gavin Schmidt writes a rather thin response to Nic Lewis's critique. Lewis has responded at length at Climate Audit.

Gavin, as might be expected, has made heavy use of his standard, "paraphrase, don't quote" technique, creating a series of strawmen that he can knock down with ease. For instance, at one point Lewis set out a great deal of evidence that suggested that land-use changes may have been omitted from a calculation. He mused about whether there was a rational explanation. Gavin paraphrased this as [my emphasis]:

Lewis in subsequent comments has claimed without evidence that land use was not properly included in our historical runs, and that there must be an error in the model radiative transfer.

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Real-world efficacies

BH readers have long been aware that low estimates of climate sensitivity based on observations are little affected by the pause and will therefore be little affected by this year's El Nino either. The discussion in this area will continue to focus on subjects like efficacies and aerosols. Marvel and colleagues are apparently formulating a response to Nic Lewis's critique, which is sure to be interesting. While we're waiting, I have been passed a preprint of a forthcoming Piers Forster paper in Annual Review of Earth and Planetary Sciences, which makes some interesting observations on the efficacy debate.

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Captain Marvel comes unstuck

While everyone else was out partying on Hogmanay, Bob Ward was hard at work writing tweets about global warming. Let noone say he is not a strangely obsessive personality.

A new paper on climate sensitivity that @mattwridley and other peddlers of denial will pretend does not exist: https://t.co/RJWJFNODkR

— Bob Ward (@ret_ward) December 31, 2015

This was a bit of a silly thing for Bob to say though because I had written a post about the said paper, by Marvel et al, some two weeks earlier, noting that it looked a bit unphysical in places.

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The extraordinary climate effect of land-use change

The latest attempt to conjure up a hypothesis as to why things are going to get much worse on the climate front has appeared in Nature Climate Change, with an author team including Gavin Schmidt and Kate Marvel.

The paper delves deeper into the idea of forcing efficacy, a concept that is explained as follows:

The concept of radiative forcing is used to compare the effects of different physical drivers on the Earth's energy budget. Two forcing agents that produce a similar radiative imbalance might be expected to initiate similar feedbacks and have the same global mean temperature response. However, there can be variations in the size and type of feedbacks engendered by a specific forcing, mainly due to geographical variations in the forcing magnitude. These variations can be characterized by an efficacy that scales for the differences in temperature response. Forcings that project more strongly on the Northern Hemisphere, land or polar regions are systematically more effective at changing temperatures than an equivalent amount of CO2, whose forcing is more uniformly distributed throughout the globe. The converse is true for forcings localized in the Southern Hemisphere or ocean regions.

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Quote of the day, epic noodle edition

Ridley and Peiser claim that research is increasingly showing climate sensitivity to be low. This is entirely the opposite of what has been happening. The most likely range of values of climate sensitivity (the amount of increase in surface temperature that eventually occurs as a result of the doubling of CO2 in the atmosphere) was established over a century ago. Recently revealed documents show that Exxon Mobil Corporation itself studied climate science as early as the late 70’s, and its findings were in clear agreement with the National Academy of Science 1979 report, which estimated a climate sensitivity of 3°C, plus or minus 1.5° C. Tables in Exxon’s 1982 Climate Change “Primer” for executives show predictions for 2015 markedly similar to contemporary estimates by NASA, and NOAA.

Greg Laden explains that a stream of evidence for low climate sensitivity cannot exist, because in the 1970s people agreed that climate sensitivity was high.

I gather that our friend ATTP found this a powerful and persuasive argument.

Puffed rice

Here's an interesting wrinkle in climate science that I hadn't thought about before. It came up in a thread at Ken Rice's place, underneath an article about carbon dioxide reductions.

The specific claim of interest was that "the amount of warming depends almost linearly on cumulative emissions". This is a claim that you hear quite often, with the corollary being that even if we halt carbon dioxide emissions, temperatures are going to remain high for centuries. However, it seems that the scientific veracity of the statement is not exactly set in stone, as Nic Lewis points out in the comments.

For the record, whilst this may be true for simulations by most current Earth system models, it is an entirely model dependent result. So please don’t present it as if a fact. If one builds a model with a low ECS, and moderate climate-cycle feedbacks, warming peaks immediately if emissions cease and declines quite rapidly thereafter. Which would happen in the real climate system is not as yet known, of course.

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Another Lew paper

Updated on Sep 16, 2015 by Bishop Hill

Stefan Lewandowsky's latest paper is out today in the Bulletin of the American Meteorological Society and features none other than Naomi Oreskes as a co-author, with the scientific oomph coming from CSIRO's James Risbey. With a roster of authors like that I think it's fair to say that one knows what to expect.

The paper is about the pause in surface temperature rises and is an attempt to demonstrate that it doesn't exist. Not very interesting I hear you say. However, the paper is not without its moments of controversy. In particular, this paragraph jumped out at me.

...some researchers (albeit a minority) have taken the “pause” to imply that the climate system may be less sensitive to greenhouse gas emissions than previously thought (Lewis 2013; Otto et al. 2013; Curry 2014; Lewis and Curry 2014).

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Climate sensitivity - just as we thought

Nic Lewis has a new paper out at Climate Dynamics, which provides new estimates of effective climate sensitivity and transient climate response. This is in essence an update to Lewis 2014, with better data. The results are very similar, with ECS at 1.66 and TCR at 1.37.

There's a technical post about the paper at Climate Audit and a preprint here.

Tamsin on climate sensitivity, lukewarmers and what we risk

As a pearl in the dunghill of the Guardian's climate change coverage, Tamsin Edward's wise article today is going to take quite a lot of beating. It attempts to sideline the namecallers, pointing to the areas of agreement and sensible disagreement in the climate debate, particularly over climate sensitivity, and ends on these very pertinent questions.

But whether we are in denial, lukewarm or concerned about global warming, the question really boils down to how we view uncertainty. If you agree with mainstream scientists, what would you be willing to do to reduce the predicted risks of substantial warming? And if you’re a lukewarmer, confident the Earth is not very sensitive, what would be at risk if you were wrong?

For a mainstream scientist, are you confident enough in your computer simulations to argue that they support the need for the shifting of resources away from dealing with the problems of today - clean water and energy for developing countries are obvious candidates - and towards the problems of the next century?

The shonky cost of carbon

A new paper has appeared in Nature Climate Change which puts a social cost of global warming at $200 per ton of carbon dioxide. The authors are Frances Moore and Delavane Diaz of Stanford.

The SCC is of course is a figure that greens can manipulate pretty much to their hearts' content - witness Frank Ackerman's hilarious $1000 figure of a few years back. The entertainment comes in working out what particular dodges have been pulled to hike the figure upwards and the new paper explains that it is picking up on an earlier study by Dell et al, which sought to make revised estimates of the damage that climate change would cause by examining the effect of short-term fluctuations in the weather on economic output.

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Lewis on the SciAm article

This article, by Nic Lewis, is crossposted from Climate Audit.

A Scientific American article concerning Bjorn Stevens’ recent paper “Rethinking the lower bound on aerosol radiative forcing” has led to some confusion. The article states, referring to a blog post of mine at Climate Audit, “The misinterpretation of Stevens’ paper began with Nic Lewis, an independent climate scientist.”. My blog post showed how climate sensitivity estimates given in Lewis and Curry (2014) (LC14) would change if the estimate for aerosol forcing from Stevens’ recent paper were used instead of the estimate thereof given in the IPCC 5th Assessment Working Group 1 report (AR5 WG1). To clarify, Bjorn Stevens has never suggested that my blog post misinterpreted or misrepresented his paper.

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