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« Reactions to Otto et al | Main | This house would stop the annual UN climate summits »

New energy-budget-derived estimates of climate sensitivity and transient response in Nature Geoscience

This is a guest post by Nic Lewis. Please note that although the embargo on the paper was lifted at 6pm, at time of writing the paper itself had yet to appear on the Nature website. It should be at the link given below in the near future.

Readers may recall that last December I published an informal climate sensitivity study at Bishop Hill, here. The study adopted a heat-balance (energy budget) approach and used recent data, including satellite-observation-derived aerosol forcing estimates. I would like now to draw attention to a new peer-reviewed climate sensitivity study published as a Letter in Nature Geoscience, "Energy budget constraints on climate response", here. This study uses the same approach as mine, based on changes in global mean temperature, forcing and heat uptake over 100+ year periods, with aerosol forcing adjusted to reflect satellite observations. Headline best estimates of 2.0°C for equilibrium climate sensitivity (ECS) and 1.3°C for the – arguably more policy-relevant – transient climate response (TCR) are obtained, based on changes to the decade 2000–09, which provide the best constrained, and probably most reliable, estimates. The 5–95% uncertainty ranges are 1.2–3.9°C for ECS and 0.9–2.0°C for TCR. I should declare an interest in this study: you will find my name included in the extensive list of authors: Alexander Otto, Friederike E. L. Otto, Olivier Boucher, John Church, Gabi Hegerl, Piers M. Forster, Nathan P. Gillett, Jonathan Gregory, Gregory C. Johnson, Reto Knutti, Nicholas Lewis, Ulrike Lohmann, Jochem Marotzke, Gunnar Myhre, Drew Shindell, Bjorn Stevens, and Myles R. Allen. I am writing this article in my personal capacity, not as a representative of the author team.

The Nature Geoscience paper, although short, is in my view significant for two particular reasons.
First, using what is probably the most robust method available, it establishes a well-constrained best estimate for TCR that is nearly 30% below the CMIP5 multimodel mean TCR of 1.8°C (per Forster et al. (2013), here). The 95% confidence bound for the Nature Geoscience paper's 1.3°C TCR best estimate indicates some of the highest-response general circulation models (GCMs) have TCRs that are inconsistent with recent observed changes. Some two-thirds of the CMIP5 models analysed in Forster et. al (2013) have TCRs that lie above the top of the 'likely' range for that best estimate, and all the CMIP5 models analysed have an ECS that exceeds the Nature Geoscience paper's 2.0°C best estimate of ECS. The CMIP5 GCM with the highest TCR, per the Forster et. al (2013) analysis, is the UK Met. Office's flagship HadGEM2-ES model – see their webpage "Advanced climate modelling for policymakers" and their document "Advance: Improved advice for science mitigation advice". The uncertainty distribution for the Nature Geoscience paper's best TCR estimate of 1.3°C indicates that it is extremely unlikely that real-world TCR is as high as that of the HadGEM2-ES model. It has a TCR of 2.5°C, nearly double 1.3°C and 0.5°C beyond the top of the 5–95% uncertainty range. The paper obtains similar, albeit less well constrained, best estimates using data for earlier periods than 2000–09.

Secondly, the authors include fourteen climate scientists, well known in their fields, who are lead or coordinating lead authors of IPCC AR5 WG1 chapters that are relevant to estimating climate sensitivity. Two of them, professors Myles Allen and Gabi Hegerl, are lead authors for Chapter 10, which deals with estimates of ECS and TCR constrained by observational evidence. The study was principally carried out by a researcher, Alex Otto, who works in Myles Allen's group.

Very helpfully, Nature's editors have agreed to make the paper's main text freely available for a limited period. I would encourage people to read the paper, which is quite short. The details given in the supplementary information (SI) enable the study to be fully understood, and its results replicated. The method used is essentially the same as that employed in my December study, being a more sophisticated version of that used in the Gregory et al. (2002) heat-balance-based climate sensitivity study, here. The approach is to draw sets of samples from the estimated probability distributions applicable to the radiative forcing produced by a doubling of CO2-equivalent greenhouse gas atmospheric concentrations (F) and those applicable to the changes in mean global temperature, radiative forcing and Earth system heat uptake (ΔT, ΔF and ΔQ), taking into account that ΔF is closely correlated with F. Gaussian (normal) error and internal climate variability distributions are assumed. ECS and TCR values are computed from each set of samples using the equations:

            (1) ECS = F ΔT / (ΔF − ΔQ)              and                  (2) TCR = F ΔT / ΔF .

With sufficient sets of samples, probability density functions (PDFs) for ECS and TCR can then be obtained from narrow-bin histograms, by counting the number of times the computed ECS and TCR values fall in each bin. Care is needed in dealing with samples where any of the factors in the equations are negative, to ensure that each is correctly included at the low or high end when calculating confidence intervals (CIs). Negative factors occur in a modest, but significant, proportion of samples when estimating ECS using data from the 1970s or the 1980s.

Estimates are made for ECS and TCR using ΔT, ΔF and ΔQ derived from data for the 1970s, 1980s, 1990s, 2000s and 1970–2009, relative to that for 1860–79. The estimates from the 2000s data are probably the most reliable, since that decade had the strongest forcing and, unlike the 1990s, was not affected by any major volcanic eruptions. However, although the method used makes allowance for internal climate system variability, the extent to which confidence should be placed in the results from a single decade depends on how well they are corroborated by results from a longer period. It is therefore reassuring that, although somewhat less well constrained, the best estimates of ECS and TCR using data for 1970–2009 are closely in line with those using data for the 2000s. Note that the validity of the TCR estimate depends on the historical evolution of forcing approximating the 70-year linear ramp that the TCR definition involves. Since from the mid-twentieth century onwards greenhouse gas levels rose much faster than previously, that appears to be a reasonable approximation, particularly for changes to the 2000s.

I have modified the R-code I used for my December study so that it computes and plots PDFs for each of the five periods used in the Nature Geoscience study for estimating ECS and TCR. The resulting ECS and TCR graphs, below, are not as elegant as the confidence region graphs in the Nature Geoscience paper, but are in a more familiar form. For presentation purposes, the PDFs (but not the accompanying box-and-whisker plots) have been truncated at zero and the upper limit of the graph and then normalised to unit total probability. Obviously, these charts do not come from the Nature Geoscience paper and are not to be regarded as associated with it. Any errors in them are entirely my own.

The box-and-whisker plots near the bottom of the charts are perhaps more important than the PDF curves. The vertical whisker-end bars and box-ends show (providing they are within the plot boundaries) respectively 5–95% and 17–83% CIs – 'very likely' and 'likely' uncertainty ranges in IPCC terminology – whilst the vertical bars inside the boxes show the median (50% probability point). For ECS and TCR, whose PDFs are skewed, the median is arguably in general a better central estimate than the mode of the PDF (the location of its peak), which varies according to how skewed and badly-constrained the PDF is. The TCR PDFs (note the halved x-axis scaling), which are unaffected by ΔQ and uncertainty therein, are all better constrained than the ECS PDFs.

The Nature Geoscience ECS estimate based on the most recent data (best estimate 2.0°C, with a 5–95% CI of 1.2–3.9°C) is a little different from that per my very similar December study (best estimate 1.6°C, with a 5–95% CI of 1.0–2.9°C, rounding outwards). The (unstated) TCR estimate implicit in my study, using Equation (2), was 1.3°C, with a 5–95% range of 0.9–2.0°C, precisely in line with the Nature Geoscience paper. In the light of these comparisons, I should perhaps explain the main differences in the data and methodology used in the two studies:

1) The main difference of principle is that the Nature Geoscience study uses GCM-derived estimates of ΔF and F. Multimodel means from CMIP5 runs per Forster et al. (2013) can thus be used as a peer-reviewed source of forcings data. ΔF is accordingly based on simulations reflecting the modelled effects of RCP 4.5 scenario greenhouse gas concentrations, aerosol abundances, etc. My study instead used the RCP 4.5 forcings dataset and the F figure of 3.71°C reflected in that dataset; I adjusted the projected post-2006 solar and volcanic forcings to conform them with estimated actuals. Use of CMIP5-based forcing data results in modestly lower estimates for both ΔF and F (3.44°C for F). Since CO2 is the dominant forcing agent, and its concentration is accurately known, the value of ΔF is closely related to the value of F. The overall effect of the difference in F on the estimates of ECS and TCR is therefore small. As set out in the SI, an adjustment of +0.3 Wm−2 to 2010 forcing was made in the Nature Geoscience study in the light of recent satellite-observation constrained estimates of aerosol forcing. On the face of it, the resulting aerosol forcing is slightly more negative than that used in my December study.

2) The Nature Geoscience study derives ΔQ using the change in estimated 0–2000 m ocean heat content (OHC) – which accounts for most of the Earth system heat uptake – from the start to the end of the relevant decade (or 1970–2009), whereas I computed a linear regression slope estimate using data for all years in the period I took (2002–11). Whilst I used the NODC/NOAA OHC data, which corresponds to Levitus et al. (2012), here, for the entire 0–2000 m ocean layer, the Nature Geoscience study splits that layer between 0–700 m and 700–2000 m. It retains the NODC/NOAA Levitus OHC data for the 700–2000 m layer but uses a different dataset for 0–700 m OHC – an update from Domingues et al. (2008), here.

3) The periods used for the headline results differ slightly. I used changes from 1871–80 to 2002–11, whilst the Nature Geoscience study uses changes from 1860–79 to 2000–09. The effects are very small if the CMIP5 GCM-derived forcing estimates are used, but when employing the RCP 4.5 forcings, switching to using changes from 1860–79 to 2000–09 increases the ECS and TCR estimates by around 0.05°C.

Since the Nature Geoscience study and my December study give identical estimates of TCR, which are unaffected by ΔQ, the difference in their estimates of ECS must come primarily from use of different ΔQ figures. The difference between the ECS uncertainty ranges of the two studies likewise almost entirely reflects the different central estimates for ΔQ they use. The ECS central estimate and 5–95% uncertainty range per my December heat-balance/energy budget study were closely in line with the preferred main results estimate for ECS, allowing for additional forcing etc. uncertainties, per my recent Journal of Climate paper, of 1.6°C with a 5–95% uncertainty range of 1.0–3.0°C. That paper used a more complex method which, although less robust, avoided reliance on external estimates of aerosol forcing.

The take-home message from this study, like several other recent ones, is that the 'very likely' 5–95% ranges for ECS and TCR in Chapter 12 of the leaked IPCC AR5 second draft scientific report, of 1.5–6/7°C for ECS and 1–3°C for TCR, and the most likely values of near 3°C for ECS and near 1.8°C for TCR, are out of line with instrumental-period observational evidence.

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Reader Comments (50)

Now I understand why Prof. Allen is proposing the motion at the Oxford Energy Society.

May 19, 2013 at 9:28 PM | Unregistered CommenterDave Salt

Forward to Peter Lilley and Graham Stringer asap! Maybe Benny has an unexpected ally.

May 19, 2013 at 9:51 PM | Unregistered CommenterG.Watkins

Great work Nic. I mean to have published with these sixteen something that, if correct, totally changes the landscape not just for AR5 WG1 but the future of the climate debate. But I admit I haven't checked every detail. :)

May 19, 2013 at 9:56 PM | Registered CommenterRichard Drake

Congratulations, Nic. That's two high-profile papers in quick succession! If you carry on like this you might be mistaken for a mainstream climate scientist!

It does seem a little odd that the headline of the paper says "we find that the global energy budget implies a range of values for the equilibrium climate sensitivity that is in agreement with earlier estimates". How do you square that with the final para of your post?

May 19, 2013 at 10:00 PM | Unregistered Commentertilting@windmills

Congratulations to Nic Lewis. This looks like an important paper on many levels

May 19, 2013 at 10:17 PM | Registered CommenterAndy Scrase

Excellent stuff Nic.
And to have Myles Allen, who is not noted for sceptical views, on board, marks a turning point.

May 19, 2013 at 10:18 PM | Unregistered CommenterDon Keiller

Congratulations Nic.

Be sure to send John Cook and Dana a copy.

May 19, 2013 at 10:22 PM | Unregistered CommenterJack

Yes indeed. Well done Nic. The list of co-authors does appear to include a good number of those who I would categorise as being of the warmist persuasion. Looks like the scientist in them is winning through.

May 19, 2013 at 10:24 PM | Unregistered CommenternTropywins

Since Nic Lewis is involved, I think this will be worthy of study. But at the very least, if it gives players like Hegerl and Allen a face-saving opportunity to step back and distance themselves from their past, and the leaked AR5, excesses then some good may come of it. Inch by inch.

May 19, 2013 at 10:27 PM | Registered CommenterJohn Shade

I can't help feel that Dr Alexander Otto has become involved in a bit of spinning, including a farcical straw man, at the end of the BBC version of this story:

Scientists say the recent downturn in the rate of global warming will lead to lower temperature rises in the short-term.

Since 1998, there has been an unexplained "standstill" in the heating of the Earth's atmosphere.

Writing in Nature Geoscience, the researchers say this will reduce predicted warming in the coming decades.

But long-term, the expected temperature rises will not alter significantly.
"The hottest of the models in the medium-term, they are actually looking less likely or inconsistent with the data from the last decade alone," said Dr Alexander Otto from the University of Oxford.

"The most extreme projections are looking less likely than before."

The authors calculate that over the coming decades global average temperatures will warm about 20% more slowly than expected.

But when it comes to the longer term picture, the authors say their work is consistent with previous estimates. The IPCC said that climate sensitivity was in the range of 2.0-4.5C.
Ocean storage

This latest research, including the decade of stalled temperature rises, produces a range of 0.9-5.0C.

"It is a bigger range of uncertainty," said Dr Otto.

"But it still includes the old range. We would all like climate sensitivity to be lower but it isn't."
"We would expect a single decade to jump around a bit but the overall trend is independent of it, and people should be exactly as concerned as before about what climate change is doing," said Dr Otto.

Is there any succour in these findings for climate sceptics who say the slowdown over the past 14 years means the global warming is not real?

"None. No comfort whatsoever," he said.


May 19, 2013 at 11:01 PM | Registered CommenterRichard Drake

[Snip O/T]

May 19, 2013 at 11:28 PM | Unregistered CommenterSpoon Jar-Jar / Jar-Jar Spoon

Well spotted Spoon Jar-Jar / Jar-Jar Spoon. I propose this paper be withdrawn and the rest of the scientists involved -

Alexander Otto, Friederike E. L. Otto, Olivier Boucher, John Church, Gabi Hegerl, Piers M. Forster, Nathan P. Gillett, Jonathan Gregory, Gregory C. Johnson, Reto Knutti, Ulrike Lohmann, Jochem Marotzke, Gunnar Myhre, Drew Shindell, Bjorn Stevens, and Myles R. Allen

be removed (forcefully if necessary) from their academic positions.

While that's happening, here's a little Gilbert and Sullivan from HMS Pachauri for you to enjoy Spoon Jar-Jar / Jar-Jar Spoon, you little climate sleuth, you.

May 20, 2013 at 1:45 AM | Registered CommenterGrantB

I was trying to get my spoon in the honey jar jar, so I wrote to the oil company to ask for shekels, but all the sent was a couple of lousy denierii.

May 20, 2013 at 2:16 AM | Unregistered CommenterGeoff Cruickshank

The most important words in this post are ".... and it's results replicated." Thanks and congrats.

May 20, 2013 at 2:26 AM | Unregistered CommenterTom in St. Johns

The trouble with papers like this is that they make the "a priori" assumption that CO2 concentration affects global temperature as predicted by Arrhenius in 1896.

Sorry to have to tell you this but the Arrhenius' theory is false.

May 20, 2013 at 3:13 AM | Unregistered Commentergallopingcamel

Well said, Gallopingcamel. This is all just 'soft' posturing designed to cuddle up to sceptic and warmist, alike. The hard scientific fact of the matter - correlation between CO2 levels and global temperature increase - has not been established.

May 20, 2013 at 4:45 AM | Registered Commenterdeminfrance

Ignore it, or spin it? What do you think?

Guardian: Climate change: human disaster looms, claims new research

We are still gonna fry.

The problem for the Guardian is that a large number of activist readers are of the "we are all gonna die by 2050 and only we care" persuasion. Despite the ridiculous "sub-editor added" headline, this sort of thing does stop their self-flagellation.

May 20, 2013 at 5:01 AM | Unregistered CommenterJiminy Cricket

The tacit claim that "the equilibrium climate sensitivity" (TECS) exists is scientifically untenable in view of the fact that TECS is a function of the equilibrium temperature but the equilibrium temperature is not an observable.

May 20, 2013 at 5:20 AM | Unregistered CommenterTerry Oldberg

James Annan blog links a new study by Stott et al (open access) that adds a similar finding to Otto et al:

They developed a kind of sensitivity approach that they claim can be used to calibrate all CMIP5 climate models. They conclude that at least the upper 95% bound of the mean global model is too high. In Nic Lewis' post he picks out the UK Met office model as an example of too high an estimate, whereas in Stott et al it is the CSIRO model that is the high outlier. (I think Stott et al find the UK model is right in there with the pack, although the names of the models are so complicated I am not sure of this.)

Richard Betts, will you be along to defend the UK model?

May 20, 2013 at 6:51 AM | Unregistered CommenterLance Wallace

Whoops--I see that Stott himself (and two coauthors) are from the Met Office. So they seem to be supporting the generally cooler estimates of Otto et al, but there seems to be a difference of opinion about the Met Office model estimates.

May 20, 2013 at 7:02 AM | Unregistered CommenterLance Wallace


Since 1998, there has been an unexplained "standstill" in the heating of the Earth's atmosphere.

Writing in Nature Geoscience, the researchers say this will reduce predicted warming in the coming decades.

Is there any succour in these findings for climate sceptics who say the slowdown over the past 14 years means the global warming is not real?

"None. No comfort whatsoever," he said.

May 19, 2013 at 11:01 PM | Registered CommenterRichard Drake

They make it up as they go along.

May 20, 2013 at 7:03 AM | Registered CommenterMartin A

Myles Allen, you got to admire the man. A few weeks back he publishes a paper saying that there is nothing unusual about the past decade and that his estimates of the underlying rate of warming that he made in the 90s are spot on and that there has been no 'pause.'

Then he appears on Channel 4 news last weeks in a report about the 'pause' saying that it wasn't that the naughties were cool it's just that the nineties were unusually warm!

Now he's a co-author of a paper that starts off by saying, "The rate of global mean warming has been lower over the past decade than previously."

So Myles Allen is having it all ways, and is allied to all shades of opinion, and sticks by none. He should have been a politician, what with him also talking on the same side as Benny Peiser and David Rose at the Oxford Union debate.

As has been said, Myles Allen will be on the winning side - whichever one it is?

May 20, 2013 at 7:14 AM | Unregistered CommenterCCx

The New Scientist's coverage shows how this is being spun, with Marcott brought out as proof of looming catastrophe, for goodness sake, but James Annan allowed to inject some realism at the end:

A growing body of climatologists think that the climate is less sensitive to CO2 than the IPCC's best estimate, so temperatures will not rise as much as feared. "I've been arguing this for a few years," says James Annan of the JAMSTEC Yokohama Institute for Earth Sciences in Yokohama, Japan.

When Otto calculated the climate sensitivity from his data, he found it was about 2 °C – with a range of 0.9 to 5 °C – well below the IPCC's best estimate of 3 °C.

"The observations are telling us one thing and the climate models are telling us another," says Forest. He thinks the most likely range is between 2.5 and 3 °C.

For the last few years, governments have been planning to sign a deal in 2015 that will come into force in 2020. On previous estimates of the climate sensitivity, that is far too late. But if the sensitivity really is below 3 °C, we might have a shot.

"If we are lucky and the climate sensitivity is at the low end, and we have a strong agreement in 2015, then I think we stand a chance to limit climate change to 2 °C," says Corinne Le Quéré of the Tyndall Centre for Climate Change Research in Norwich, UK. "But there's a lot of ifs."

Even if it is technically possible to limit warming to 2 °C, that does not mean it will actually happen. "I suppose it means that 2 °C isn't quite as unattainable as it was previously thought to be, but I'm not exactly holding my breath on climate negotiations," says Annan.

We might have a shot of saving the world folks. Something to cheer us all up before breakfast.

May 20, 2013 at 7:22 AM | Registered CommenterRichard Drake

Martin A: Indeed. The key sentence we need to hit very hard is:

Is there any succour in these findings for climate sceptics who say the slowdown over the past 14 years means the global warming is not real?

How many sceptics do you know 'who say the slowdown over the past 14 years means the global warming is not real'? The warming since 1850 is agreed by at least 97% of us, right? :) This is a ridiculous straw man, to avoid saying what matters: that the majority of real sceptics, with Lindzen in the lead, have been arguing that climate sensitivity has to be lower than the IPCC says, simply based on what we know from the last 160 years, CO2 and temperature wise.

I know that you doubt even the CS concept Martin but if it is meaningful to speak of ECS and TCR in the modern era then surely they can't be as the models say. That has been the mainstream sceptic position. The Beeb felt it had to create a straw one.

May 20, 2013 at 7:31 AM | Registered CommenterRichard Drake

James Annan says he has been arguing for years that the earth's temperature will not rise as much as predicted!!! How they are all rewriting history. Pull the other one James. Wasn't it you who had the bet with David Whitehouse on the BBC. You said the temp would go up and break records, David Whitehouse said it would not. And guess what, David Whitehouse won. Now Annan is saying something different. Some of these climate scientists are shifting their positions hoping we don't remember their past.

May 20, 2013 at 8:01 AM | Unregistered CommenterCCx

Yes, well done Nic for instilling some rationality in Myles et al where previously little existed, but while checking Pierre's for the latest from Kirkby on CERN's CLOUD, I came across a video of Salby which suggests that this is all totally irrelevant. (watch if from 15 minutes if you are short for time).

May 20, 2013 at 8:40 AM | Registered Commenterlapogus

Retrospectively predicting what these climate "scientists" said in the past is getting to be the new climate paradigm - or something. I think we've passed a tipping point and the concensus is that 97% of climate "scientists" say that they have been right all along, despite what they said in the past.

May 20, 2013 at 8:46 AM | Registered CommenterPhillip Bratby

I have an article in the Times on this new Otto et al paper and its implications for policy.

quote from my article: “The most likely estimate is 1.3C. Even if we reach doubled carbon dioxide in just 50 years, we can expect the world to be about two-thirds of a degree warmer than it is now, maybe a bit more if other greenhouse gases increase too. That is to say, up until my teenage children reach retirement age, they will have experienced further warming at about the same rate as I have experienced since I was at school.”

May 20, 2013 at 8:50 AM | Unregistered CommenterMatt Ridley

There's a nice misleading bit of spin right at the start of the paper:

The rate of global mean warming has been lower over the past decade than previously. It has been argued that this observation might require a downwards revision of estimates of equilibrium climate sensitivity, that is, the long-term (equilibrium) temperature response to a doubling of atmospheric CO2 concentrations. Using up-to-date data on radiative forcing, global mean surface temperature and total heat uptake in the Earth system, we find that the global energy budget implies a range of values for the equilibrium climate sensitivity that is in agreement with earlier estimates, within the limits of uncertainty.

If you only read this far, you'd get the impression that the paper supports the IPCC 2-4.5 value and refutes lower values. To describe 1.2-3.9 as 'in agreement' with 2-4.5 seems somewhat misleading. I'm guessing that Nic didn't write that sentence.

May 20, 2013 at 8:52 AM | Registered CommenterPaul Matthews

I searched for a list of assumptions in this paper, but in vain. The key assumption is that in the real world, (cf the world of theory) CO2 causes a temperature increase. The problem is that no-one has yet proved that - any CO2 driven warming might be counterbalanced by other forces or might be negligible. Take a look at chapter 7 of the IPCC's 2007 report and you'll see that there's a host of problems with models.

Despite these known problems, this paper, like many others in climate science, seems to think that models are so reliable that their results cannot be questioned because they are rock-solid evidence. It's either that or the researchers are desperate to pretend that they have the answers. It's yet another area of climate science where belief is substituted for empirical evidence and fact.

May 20, 2013 at 9:10 AM | Unregistered CommenterJohnM

CCx (8:01 AM) --
Annan wrote:

[M]y previous posts on the matter actually point to a value more likely on the low side of this rather than higher, and were I pressed for a more precise value, 2.5 might have been a better choice even then. But I'd rather be a little conservative than risk being too Pollyanna-ish about it.

May 20, 2013 at 9:42 AM | Registered CommenterHaroldW

Nic -
I think it is mean of you (to Dana) not to include a mean value. ;-)

May 20, 2013 at 9:45 AM | Registered CommenterHaroldW

that was a fascinating lecture by Salby, and one which appears to tear some pretty major holes in GCM assumptions. Thank you for posting the link.

Does anyone know if this work is challenged elsewhere?

May 20, 2013 at 10:19 AM | Unregistered CommenterVarco

Harold W
"I think it is mean of you (to Dana) not to include a mean value. ;-)"

It never crossed my mind to do such an inappropriate thing!

I have realised that, somewhat confusingly, the paper says that the "most likely" value of equilibrium climate sensitivity (based on data from the 2000s) is 2.0 C. That figure is in fact both the median and the (identical, given the Gaussian error assumptions) best-fit point of maximum likelihood - as clarified in the caption to Figure 1. It is not the mode.

May 20, 2013 at 11:29 AM | Unregistered CommenterNic Lewis


Your top chart shows that the estimated pdf for climate sensitivity has been increasing without fail every decade. It's even higher for the 2000s than the 1990s, going against the line of argument that recent flatlining temperatures mean sensitivity should be revised down (which has been assumed by many on this blog and elsewhere). Instead it suggests that the lower estimates relative to the IPCC consensus are an inherent property of the energy budget approach.


May 20, 2013 at 12:38 PM | Unregistered Commentertilting@windmills

"Your top chart shows that the estimated pdf for climate sensitivity has been increasing without fail every decade"

Apart from the 1970s, an unusually cold decade and with changes in forcing and temperature too small to get a reasonably well-constrained ECS estimate, the median estimate (vertical bar in the middle of the the box-plots) varied very little between the decades.

The mode (where the PDF peaks) increased from the 1980s through the 2000s mainly because the ECS estimates were getting better constrained. That illustrates a point I make in the paragraph below the charts.

Re flatlining of temperatures in the 2000s this is explained by:

a) the average temperature in the 2000s was 0.18 C higher than the 1990s, because temperatures were much lower in the early 1990s than in the late 1990s and 2000s; and

b) based on the ocean heat dataset used, total heat uptake rose very sharply between the 1990s and the 2000s, absorbing all the increase in forcing due to rising C02 etc.

May 20, 2013 at 2:21 PM | Unregistered CommenterNic Lewis

Thanks, Nic. So do you think the post-1998 temperature trend affects estimates of climate sensitivity, or not? Seems an interesting question, especially since it has been discussed by everyone including the Mail and the Economist.

May 20, 2013 at 2:41 PM | Unregistered Commentertilting@windmills

"So do you think the post-1998 temperature trend affects estimates of climate sensitivity, or not?"

My natural inclination is to suspect that it does, but I don't as yet have a good enough understanding of the various estimates of ocean heat content to be confident whether that is, or is not, the case.

But whether or not there was much more heat going into the oceans in the 2000s than in previous decades, the standstill in temperatures post-1998 has certainly brought down the best estimate of TCR, which is probably a more policy-relevant sensitivity measure.

May 20, 2013 at 4:59 PM | Unregistered CommenterNic Lewis

Lance Wallace

You are right that the Otto et al paper says similar things to Stott et al 2013 published 3 months ago. The latter was co-authored by occasional BH poster Ed Hawkins who also blogged about it.

Incidentally, one of Otto's co-authors is also a Met Office scientist - Jonathan Gregory (he's jointly at Reading University and Met Office) so Otto et al is also partly Met Office work.

Stott et al did point out that HadGEM2-ES is at the top end of the observationally-contrained range of TCS when using the longer term contraints. Otto et al agree with that. The key thing is that the HadGEM2-ES TCR is outside the range obtained from using 2000-2009 alone, but Otto et al specifically say:

caution is required in interpreting any short period, especially a recent one for which details of forcing and energy storage inventories are still relatively unsettled

So, yes, we are well aware that HadGEM2-ES has a relatively high TCR, and have pointed this out ourselves, but I'm not so sure that it can be discounted as Nic seems to think. But in any case, it's common practice to use the whole ensemble of CMIP models like Ed Hawkins does, and as Otto et al point out:

Most of the CMIP5 ensemble are, however, consistent with the observations used here in terms of both ECS and TCR

May 20, 2013 at 5:06 PM | Registered CommenterRichard Betts

Dr Betts -
HadGEM2 is listed in Forster et al. as having the highest TCR (2.5 K) and second-highest ECS (4.59 K) among 19 CMIP5 models. Both values are inconsistent (at the 5% level) with the results of Otto et al.

Of the 19 models, six of them have an ECS outside Otto's 5-95% range of 1.2-3.9K. Five of them have a TCR outside its range of 0.9 - 2.0 K, with an additional five at 2.0 K. All of these exceptional values are above the specified range. So while most may still be "consistent with" Otto et al., it's clear that the multi-model mean is biased high.

Only three of the nineteen have TCR values equal to or less than Otto's best estimate of 1.3 K. To my mind, "consistent with" sounds more like "not yet shown to be inconsistent with".

May 20, 2013 at 6:19 PM | Registered CommenterHaroldW

I've removed a comment that was almost certainly libellous and responses to it.

May 20, 2013 at 9:45 PM | Registered CommenterBishop Hill

Obviously you cannot be seen to criticise authors in here, for their past indiscretions ..... hmmmm

How Not to be seen ?

"However, although the method used makes allowance for internal climate system variability, the extent to which confidence should be placed in the results from a single decade depends on how well they are corroborated by results from a longer period."

Clearly this stems from a misunderstanding ?

The logic in that premiss is faulty, this is naught but, post hoc ergo propter hoc

May 20, 2013 at 11:08 PM | Unregistered CommenterSpoon the Moon

that was a fascinating lecture by Salby, and one which appears to tear some pretty major holes in GCM assumptions. Thank you for posting the link.

Does anyone know if this work is challenged elsewhere?
May 20, 2013 at 10:19 AM Varco

There is no shortage of people ridiculing Salby - see the skepticalscience website. But my impression is that:
1. They are midgets in comparison to his stature.
2. They are jumping in to rubbish his conclusions without having fully taken in what he says.

May 20, 2013 at 11:47 PM | Registered CommenterMartin A

Had the global average temperatures been at the upper limit of IPCC predictions for the past fifteen years, would the estimates of CS be any different from those currently being made?

If "yes", is this because actual temperatures are inputs into the computation of estimates of CS? Or for some other reason?

May 20, 2013 at 11:54 PM | Registered CommenterMartin A

MartinA -
Temperatures are most definitely inputs to the estimates of CS in this approach. From the paper's equations (1) and (2), ECS and TCR are both proportional to the temperature change.

The central values used in the CS calculation for the 2000s are (from the SI, Table S1):
Temperature 0.75 K
Forcing 1.95 Wm-2
System heat uptake 0.65 Wm-2
[Relative to the reference period of 1860-1879.]

Plugging these values (plus the assumed forcing for a CO2 doubling of 3.44 Wm-2) into the paper's formulas, yields values of 2.0 K/doubling for ECS and 1.3 K for TCR.

If temperatures had risen post-1998 at the AR4 multi-model mean value of 0.22 K/decade, the average temperature anomaly of the 2000s would have been about 0.9 K rather than the observed 0.75 K. The ECS and TCR central estimates would increase in the ratio of 0.9/0.75=1.2, becoming 2.4 K and 1.6K respectively.

May 21, 2013 at 1:36 PM | Registered CommenterHaroldW

HaroldW - thank you.

May 21, 2013 at 3:25 PM | Unregistered CommenterMartin A

From the "paper"
"Gaussian (normal) error and internal climate variability distributions are assumed."

May 20, 2013 at 3:13 AM | gallopingcamel gets it. ....
"they make the "a priori" assumption" .... Arrhenius' theory ... etc.
(The entire paper is reliant on this assumption.)


"I searched for a list of assumptions in this paper, but in vain. The key assumption is that in the real world, (cf the world of theory) CO2 causes a temperature increase. The problem is that no-one has yet proved that." .... May 20, 2013 at 9:10 AM | JohnM

Precisely so John. This is the real argument actually. Show us the real life proof, the irrefutable empirical evidence, not this incessant filibuster of buncombe, and endless nit-picking about the finer points of this computer model "correction" factor, or that minor "adjustment" of the retrograde checking procedure, in relation to the infinitesimal change in the concentration of CO2 measured on the slopes of an active volcano. If Mr. Lewis or any of the other Authors of the document tell me this is "science", then I say "science" is an ass! Lets get back to Logic and Empirical Evidence. We cannot allow hokum theroies and bogus ideas to remain unchallenged, for to do so would risk causing the deaths of countless millions, due to malnutrition, and ill health. We owe it to ourselves to be true to ourselves, and stop these charades, and get back to the real world now !
/ rant mode off

Again "major holes in GCM assumptions (in lecture by Salby)
May 20, 2013 at 10:19 AM | Varco pointed out, and yes I saw that, and his earlier presentations. I do recommend doing some few experiments for yourself, then you can see with YOUR OWN EYES, what is true and what isn't.

Remember the great Arrhenius, clever though he may have been, had very primitive instruments and methods, compared with what we have today. So it is possible to use a handheld CO2 meter, and go into a cornfield in East Anglia, at noon, in the summertime, and measure virtually no CO2 at all. Then again go into the centre of Moscow, at midnight, in mid-winter and measure well over 1000ppm. Maybe take the meter into a public bar, or busy restaurant, or theatre, and be shocked that you aren't dead, or been boiled alive, by the massive temperature rise that should have occurred at levels approaching 2000ppm or more ! Ahhhhrgg we're aaa doomed - (c) Pte Fraser - "Dad's Army".


"given the Gaussian error assumptions"
May 20, 2013 at 11:29 AM | Nic Lewis

there is that word again ....sigh :-(


"which has been assumed by many on this blog and elsewhere"
May 20, 2013 at 12:38 PM | tilting@windmills
"Es Muy Importante - Adelante" -- Sash!

May 21, 2013 at 1:36 PM | HaroldW
"assumed forcing"

I assume that maybe some people would wish to hear some music whils they read through, and mull over what I wrote. And for the avoidance of all doubt, I am advocating that we return to the true "scientific method", of the "Seeker after Truth".

ADELANTE - nearly a million and a half people , now that's what I call a "consensus" !

May 21, 2013 at 6:25 PM | Unregistered CommenterSash!

Nic and Richard,

I seem to recall that ocean heat content increases have been slowing in the last 8-10 years. Am I thinking of something else? Can you point me to the data?

May 22, 2013 at 6:26 AM | Unregistered CommenterDavid Young

Martin A: "They make it up as they go along."

I don't know whether it's a career saving move, keeping to the party line, or it's a genuine attempt to keep the funding rolling in, but either way there's massive hubris in any profession that believes they can foretell the future state of a coupled non-linear chaotic climate system. At least that's what the IPCC used to say before it was hi-jacked by activists.

As an aside, I don't believe the climate has any appreciable sensitivity. To me it would seem clear that there must have been times when the temperature has increased above 1C, so we'd have had the forecast feedbacks and there would be evidence of a subsequent 2 - 4.5C rise. I don't know of any so am assuming

May 22, 2013 at 10:03 AM | Unregistered Commentergeronimo

Why was it "off topic" to point out that the author of this piece
is in fact a failed accountant of a bankrupt company, and not
in fact a "scientist" of any sort ?

from the "memory hole" about Nic Lewis

"According to UK Companies House Records,

*Nic Lewis was director . accountant of BIG REALISATIONS LIMITED
appointed 29 Nov 2002 and resigned on 6 Dec 2004, shortly
after the business went belly-up owing millions of pounds.

listed by UK companies house as being at ...

Nic Lewis is an "Accountant", of a firm which collapsed
owing millions of pounds, is that right? So now some
years later, he is pontificating on the latest climate
wish-wash, and we are to believe that he is the only
genuine scientist among that throng of "apologists".

It's all in the Public Record at Companies House."

*Full Name = Nicholas Howard Lewis, for it is he.


Update by the Memory Hole.

That previous information originally provided by "Spoon Jar Jar"
was certainly not libellous, because it is in the public record,
however when Nic Lewis worked there the company name was
actually "BFS INCOME & GROWTH TRUST PLC", and the so called
"Big Realisations" was in fact a tongue in cheek reference to their
liquidation of all their assets. The company changed it's name to
"Big Realisations" shortly after Nic Lewis left and the appalling
state of the company accounts were exposed by new accountants.

see the appalling performance figures,
when Nic Lewis was a director there -

company history here -

I ask you, is this the track record of a person who ought to
be pontificating about whether the science or even scientists
are genuine or not ?

Jun 5, 2014 at 3:03 AM | Unregistered CommenterMemory Hole

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