After the House of Lords debate on the Energy Bill, Lord Deben wrote to a group of peers attacking the statements made by Matt Ridley in the debate. The letter and the ensuing correspondence was as follows:
Deben's first letter was sent on 4 July 2013:
My Lords,
During the debate on July 2, on the Energy Bill, I stated that the arguments on the science presented by my noble friend Lord Ridley were at variance with the views of the overwhelming majority of scientists whose expertise bears on these issues. I owe it to Lord Lawson, upon whom I intervened, and the noble Viscount to justify that statement. I therefore list the basis for that assertion and append two recent articles which address the points that he raised.
- Climate sensitivity measures the increase in temperature due to a doubling of carbon in the atmosphere.
- Climate sensitivity has always been uncertain, and remains so.
- When we, the Committee on Climate Change, advised the Government and Parliament on the 2050 target in the Climate Change Act, we modelled climate sensitivity on the range suggested by the IPCC.
- There have been a number of studies since then which have found climate sensitivity within the range that we modelled, some at the lower end of the range, and some at the higher end of the range.
- There is no scientific evidence to suggest that the range has significantly changed, or that the probability distribution within this range has significantly changed.
- Matt Ridley draws in particular on a recent study published in Nature Geoscience, which gives a best estimate of climate sensitivity at the low end of IPCC range. However, this study makes assumptions on highly uncertain variables, and should not be regarded as definitive (as no single study should be).
- It is appropriate to consider the full range of uncertainty in order to make decisions that appropriately balance future risks.
- Assessment against the full range of uncertainty suggests the need to cut UK emissions by at least 80% in 2050 as part of global emissions reductions to limit risks of dangerous climate change.
- Within this, it is essential to move to a low-carbon power sector. Not to do this would raise the costs and risks of meeting the 2050 target.
The following articles provide additional support:
This article provides a useful summary of the evidence on climate sensitivity and also highlights the issues surrounding the use of climate science in mainstream media articles. In mainstream explanation, such as in The Economist, climate science is often misunderstood and there is a failure to adequately reflect complexities and uncertainties. The article concludes that the evidence on climate sensitivity is such that we need to reduce emissions significantly in order to limit the risks of very dangerous climate change that we currently face.
This article focuses on how Matt Ridley misinterprets the science and highlights that there is more than one way to estimate climate sensitivity. There is emphasis on the range of estimates of climate sensitivity within climate models, and from other methodological approaches. The fact that a particular study suggests a lower estimate of climate sensitivity does not mean that all other evidence should now be negated. Rather, new studies should be considered in the context of the vast evidence base that exists. While some (notably Matt Ridley) have taken the results of particular studies and rejected this wider evidence, it is essential to consider the evidence base as a whole. The article concludes that the range of estimates of climate sensitivity remains unchanged, and that urgent action is required to reduce global emissions.
Lord Deben
Later the same day, Ridley replied as follows:
My Lords,
My noble friend Lord Deben has written to you today on the topic of climate sensitivity to justify what he said about my speech in the debate in Grand Committee last Tuesday. I am delighted to have the opportunity to respond, because the evidence he links to in fact rather well support the points I made. He said in the debate that the “facts that were presented [by me] would be denied by almost every climatologist in the world”, yet the sources that he supplies in his email actually vindicate the remarks I made, as I detail below.
For example, I said that the full greenhouse effect of a doubling of carbon dioxide is about 1.2C of warming. Lord Deben refers to the article by Dana Nuccitelli in the Guardian, which explicitly confirms that I am correct: “if we double the amount of carbon dioxide in the atmosphere, the increased greenhouse effect will cause the planet's average surface temperature to warm about 1.2°C (2.2°F) in response.” While I would not rely on the Guardian for accuracy, this is indeed widely agreed by scientists. So this point alone makes Lord Deben’s assertion that my facts would be denied by almost every climatologist false.
I am delighted to have this opportunity of emphasizing the general agreement among scientists on this point because it is often overlooked among journalists and politicians thatdoubling carbon dioxide alone cannot produce dangerous levels of global warming. As I said in the debate, this risk comes from putative net water-vapour and cloud feedbacks, as confirmed in Mr Nuccitelli’s Guardian article cited by Lord Deben. Mr Nuccitelli claims that a recent study finds water vapour concentration rising as predicted in the models. But this is just one paper and others find no such effect. For example a paper published last year concluded:
“Therefore, at this time, we can neither prove nor disprove a robust trend in the global water vapor data.”
http://onlinelibrary.wiley.com/doi/10.1029/2012GL052094/abstract
And a recent essay summarized the data thus:
“Climate models predict upper atmosphere moistening which triples the greenhouse effect from man-made carbon dioxide emissions. The new satellite data from the NASA water vapor project shows declining upper atmosphere water vapor during the period 1988 to 2001. It is the best available data for water vapor because it has global coverage.”
(http://www.friendsofscience.org/assets/documents/NVAP_March2013.pdf)
Besides, the IPCC AR4 report itself is clear that on top of any effect from water vapour, changes in clouds can either amplify or dampen warming by at least as much as water vapour and CO2, so there is no consensus about likely amplification of CO2-induced warming.
Furthermore, as I stated in my speech, the empirical data on global mean temperature confirm that warming has been much slower than predicted in all models, as shown in the following chart from Reading University, used by The Economist:
Lord Deben claims that I have chosen a few unrepresentative studies of climate sensitivity. This is not the case. I show below a chart on which are the 95% confidence intervals for observationally-based peer-reviewed studies on climate sensitivity published since 2010, all of which are on average lower than the IPCC’s central 3C estimate. Far from me being the one who is cherry-picking a study to suit my prejudices, it is Mr Nuccitelli who is cherry-picking by citing a single study of climate sensitivity that gives a climate sensitivity estimate based on a number of sources, all of which are derived from paleoclimate work, a notoriously unreliable way of estimating this variable.
Many climate sensitivity studies depend on highly complex global climate models (GCMs), and reflect the characteristics of the model concerned rather than those of the real climate. Even GCM-based studies that purport to provide properly observationally-constrained estimates of climate sensitivity, by running many simulations of the GCM with different parameter settings and comparing the results withobservations, may in fact rule out a priori the possibility of climate sensitivity being below the IPCC likely range. A good example is two recentstudies by Met Office scientists, Sexton et al 2012 and Harris et al 2013, the techniques of which formed the basis for UKCP09, a set of projections for UK climate for the 21st century. The use of the Met Office's HadCM3 model for these studies guaranteed that they would produce high climate sensitivity estimates, almost regardless of what best estimates the observational data used pointed to.
In case I should be accused of misrepresenting the studies finding low climate sensitivity, let me quote from them directly:
From Ring et al. (2012):
“Additionally, our estimates of climate sensitivity using our [simple climate model] and the four instrumental temperature records range from about 1.5°C to 2.0°C. These are on the low end of the estimates in the IPCC’s Fourth Assessment Report. So, while we find that most of the observed warming is due to human emissions of [long-lived greenhouse gases], future warming based on these estimations will grow more slowly compared to that under the IPCC’s “likely” range of climate sensitivity, from 2.0°C to 4.5°C.”
From van Hateren (2012):
“The millennium-scale response to doubling of the CO2 concentration found here, 2.0 ± 0.3°C, thus has presumably not yet reached full equilibrium, and can therefore only be cautiously compared with the equilibrium climate response of the 2007 IPCC report (Meehl et al 2007). It is at the lower end of the range considered likely (2-4.5°C), and lower than its best estimate (3°C).”
From Aldrin et al. (2012):
“The mean is 2.0°C… which is lower than the IPCC estimate from the IPCC Fourth Assessment Report (IPCC,2007), but this estimate increases if an extra forcing component is added, see the following text. The 95% credible interval (CI) ranges from 1.1°C to 4.3°C, whereas the 90% CI ranges from 1.2°C to 3.5°C.”
From Masters (2013) (not yet included in the chart):
"This method yields a median estimate for ECS [equilibrium climate sensitivity] of 1.98 K, with a likely (67 %) range of 1.47–2.95 K and a 90 % confidence interval of 1.19–5.15 K." (1 K = 1°C).
From Lewis (2013, in press [Journal of Climate]):
"Employing the improved methodology, preferred 90% bounds of 1.2-2.2 K for ECS are then derived (mode and median 1.6 K). ...Incorporating forcing and observational surface temperature uncertainties, unlike in the original study, widens the 90% range to 1.0-3.0 K."
In addition, there is the Otto et al (2013) study in Nature Geoscience to which I referred in my speech and which has been characterized as follows by one of its authors, Nic Lewis:
“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. It has a TCR of 2.5°C, nearly double the Nature Geoscience paper’s best estimate of 1.3°C and 0.5°C beyond the top of the 5–95% uncertainty range.”
Mr Lewis has also written as follows in response to a comment from Mr Nuccitelli:
“If climate sensitivity is two-thirds or less than the IPCC's central estimate, then for any greenhouse gas emissions scenario ultimate anthropogenic global warming will be at least a third less than previously expected.”
In short, I stand by my assertion in the debate that recent scientific opinion has not been moving in the direction of greater alarm, but the reverse.
I am surprised that Lord Deben should cite an article on a blog called the Carbon Brief. This was based largely on a Guardian article by Myles Allen, which misrepresented me. I append below the text of a letter I wrote to Professor Allen in response.
Finally, I am delighted to see Lord Deben concede that "Climate sensitivity has always been uncertain, and remains so". However, this flies in the fact of his repeated assertions of sufficient certainty about climate risk to base veryexpensive policy upon it.
Yours sincerely,
Matt Ridley.
The following day, Deben had another go.
My Lords,
In his response to my explanation, Viscount Ridley dismisses vast swathes of the scientific evidence base:
- He assumes away positive feedbacks which amplify the initial warming due to increased carbon in the atmosphere, without having robust evidence to justify this.
- He rejects climate modelling, and methodologies which estimate climate sensitivity based on historical data, both of which are major areas of research.
- He focuses on a particular study within the energy balance modelling approach. What he doesn’t say is that this paper suggests estimates of climate sensitivity that are largely unchanged based on recent temperature data, and that it implies the need to cut global emissions significantly in order to limit currently high risks of very dangerous climate change. Neither does he refer to other studies within this approach which find a higher sensitivity. He does not highlight the limitations of energy balance modelling, which is no more certain than climate modelling.
It is the job of the Committee on Climate Change to consider the scientific evidence in its entirety, and in a balanced and open-minded way. The scientific evidence continues to suggest significant risks of very dangerous climate change. We should insure against this through reducing emissions, which we can do at relatively low cost.
I do not propose to continue this discussion further in public but will instead seek to arrange a meeting between Viscount Ridley and the climate scientists who work for the Committee on Climate Change.
Lord Deben
And finally
6.7.13
My Lords,
Lord Deben has once again written to you. In response, briefly, to his letter I would make three points:
First, far from "assuming away" positive feedbacks that amplify the initial warming due to increased carbondioxide levels, I pointed out that recent observational evidence pointed topositive feedbacks in the real world being much weaker than those exhibitedwithin complex global climate models' virtual worlds.
Second, I am always happy to meet any scientists to discuss climate change. It would be most profitable if we wereaccompanied by other scientists who have reached different conclusionsthan those the CCC has consulted, so that the exchange could be a two-way one. I assume Lord Deben would agree to attend also.
Third, you should know that this is not the first time I have been wrongly cited in this way. Lord Deben made an unprovoked attack on me several months ago in a lecture in Oxford, charging – on the basis of a blog post written by a novelist – that I had not cited the mainstream scientific literature when writing about ocean acidification. In fact I had included direct quotations from 17 papers in the mainstream scientific literature, including a major meta-analysis of 372 peer-reviewed papers. Despite being requested twice to do so, LordDeben declined to write to the organisers of the lecture to correct his mistake.
Yours sincerely
Matt Ridley
Bishop Hill
I inadvertently missed the final email in this exchange. I've added it now, so if you read the original post before 9:30 you might like to revisit.