We are a little late to the party, but it is worth adding a few words now that our favourite amateur contrarian is at it again. As many already know, the Forum on Physics and Society (an un-peer-reviewed newsletter published by the otherwise quite sensible American Physical Society), rather surprisingly published a new paper by Monckton that tries again to show using rigorous arithmetic that IPCC is all wrong and that climate sensitivity is negligible. His latest sally, like his previous attempt, is full of the usual obfuscating sleight of hand, but to save people the time in working it out themselves, here are a few highlights.
As Deltoid quickly noticed the most egregious error is a completely arbitrary reduction (by 66%) of the radiative forcing due to CO2. He amusingly justifies this with reference to tropical troposphere temperatures – neglecting of course that temperatures change in response to forcing and are not the forcing itself. And of course, he ignores the evidence that the temperature changes are in fact rather uncertain, and may well be much more in accord with the models than he thinks.
But back to his main error: Forcing due to CO2 can be calculated very accurately using line-by-line radiative transfer codes (see Myhre et al 2001; Collins et al 2006). It is normally done for a few standard atmospheric profiles and those results weighted to produce a global mean estimate of 3.7 W/m2 – given the variations in atmospheric composition (clouds, water vapour etc.) uncertainties are about 10% (or 0.4 W/m2) (the spatial pattern can be seen here). There is no way that it is appropriate to arbitrarily divide it by three.
There is a good analogy to gas mileage. The gallon of gasoline is equivalent to the forcing, the miles you can go on a gallon is the response (i.e. temperature), and thus the miles per gallon is analogous to the climate sensitivity. Thinking that forcing should be changed because of your perception of the temperature change is equivalent to deciding after the fact that you only put in third of a gallon because you ran out of gas earlier than you expected. The appropriate response would be to think about the miles per gallon – but you’d need to be sure that you measured the miles travelled accurately (a very big issue for the tropical troposphere).
But Monckton is not satisfied with just a factor of three reduction in sensitivity. So he makes another dodgy claim. Note that Monckton starts off using the IPCC definition of climate sensitivity as the forcing associated with a concentration of 2xCO2 – this is the classical “Charney Sensitivity” and does not include feedbacks associated with carbon cycle, vegetation or ice-sheet change. Think of it this way – if humans raise CO2 levels to 560 ppm from 280 ppm through our emissions, and then as the climate warms the carbon cycle starts adding even more CO2 to the atmosphere, then the final CO2 will be higher and the temperature will end up higher than standard sensitivity would predict, but you are no longer dealing with the sensitivity to 2xCO2. Thus the classical climate sensitivity does not include any carbon cycle feedback term. But Monckton puts one in anyway.
You might ask why he would do this. Why add another positive feedback to the mix when he is aiming to minimise the climate sensitivity? The answer lies in the backwards calculations he makes to derive the feedbacks. At this point, I was going to do a full analysis of that particular calculation – but I was scooped. So instead of repeating the work, I’ll refer you there. The short answer is that by increasing the feedbacks incorrectly, he makes the ‘no-feedback’ temperature smaller (since he is deriving it from the reported climate sensitivities divided by the feedbacks). This reverses the causality since the ‘no-feedback’ value is actually independent of the feedbacks, and is much better constrained.
There are many more errors in his piece – for instance he accuses the IPCC of not defining radiative forcing in the Summary for Policy Makers and not fixing this despite requests. Umm… except that the definition is on the bottom of page 2. He bizarrely compares the net anthropogenic forcing to date with the value due to CO2 alone and then extrapolates that difference to come up with a meaningless ‘total anthropogenic forcings Del F_2xCO2’. His derivations and discussions of the no-feedback sensitivity and feedbacks is extremely opaque (a much better description is given on the first couple of pages of Hansen et al, 1984)). His discussion of the forcings in that paper are wrong (it’s 4.0 W/m2 for 2xCO2 (p135), not 4.8 W/m2), and the no-feedback temperature change is 1.2 (Hansen et al, 1988, p9360), giving k=0.30 C/(W/m2) (not his incorrect 0.260 C/(W/m2) value). Etc… Needless to say, the multiple errors completely undermine the conclusions regarding climate sensitivity.
Generally speaking, these are the kinds of issues that get spotted by peer-reviewers: are the citations correctly interpreted? is the mathematics correct? is the reasoning sound? do the conclusions follow? etc. In this case, there really wouldn’t have been much left, and so it is fair to conclude that Monckton’s piece only saw the light of day because it wasn’t peer-reviewed, not because it was. Claims that the suggested edits from the editor of the newsletter constitute ‘peer-review’ are belied by the editor’s obvious unfamiliarity with the key concepts of forcing and feedback – and the multitude of basic errors still remaining. The even more egregious claims that this paper provides “Mathematical proof that there is no ‘climate crisis’ ” or is “a major, peer-reviewed paper in Physics and Society, a learned journal of the 10,000-strong American Physical Society” are just bunk (though amusing in their chutzpah).
The rational for the FPS publication of this note was to ‘open up the debate’ on climate change. The obvious ineptitude of this contribution underlines quite effectively how little debate there is on the fundamentals if this is the best counter-argument that can be offered.