Cuckoo Science

Sometimes on Realclimate we discuss important scientific uncertainties, and sometimes we try and clarify some subtle point or context, but at other times, we have a little fun in pointing out some of the absurdities that occasionally pass for serious ‘science’ on the web and in the media. These pieces look scientific to the layperson (they have equations! references to 19th Century physicists!), but like cuckoo eggs in a nest, they are only designed to look real enough to fool onlookers and crowd out the real science. A cursory glance from anyone knowledgeable is usually enough to see that concepts are being mangled, logic is being thrown to the winds, and completely unjustified conclusions are being drawn – but the tricks being used are sometimes a little subtle.

Two pieces that have recently drawn some attention fit this mold exactly. One by Christopher Monckton (a viscount, no less, with obviously too much time on his hands) which comes complete with supplementary ‘calculations’ using his own ‘M’ model of climate, and one on (‘What Watt is what’). Junk Science is a front end for Steve Milloy, long time tobacco, drug and oil industry lobbyist, and who has been a reliable source for these ‘cuckoo science’ pieces for years. Curiously enough, both pieces use some of the same sleight-of-hand to fool the unwary (coincidence?).

But never fear, RealClimate is here!

The two pieces both spend a lot of time discussing climate sensitivity but since they don’t clearly say so upfront, it might not at first be obvious. (This is possibly because if you google the words ‘climate sensitivity’ you get very sensible discussions of the concept from Wikipedia, ourselves and the National Academies). We have often made the case here that equilibrium climate sensitivity is most likely to be around 0.75 +/- 0.25 C/(W/m2) (corresponding to about a 3°C rise for a doubling of CO2).

Both these pieces instead purport to show using ‘common sense’ arguments that climate sensitivity must be small (more like 0.2 °C/ W/m2, or less than 1°C for 2xCO2). Our previous posts should be enough to demonstrate that this can’t be correct, but it worth seeing how they arithimetically manage to get these answers. To save you having to wade through it all, I’ll give you the answer now: the clue is in the units of climate sensitivity – °C/(W/m2). Any temperature change (in °C) divided by any energy flux (in W/m2) will have the same unit and thus can be ‘compared’. But unless you understand how radiative forcing is defined (it’s actually quite specific), and why it’s a useful diagnostic, these similar seeming values could be confusing. Which is presumably the point.

Readers need to be aware of at least two basic things. First off, an idealised ‘black body’ (which gives of radiation in a very uniform and predictable way as a function of temperature – encapsulated in the Stefan-Boltzmann equation) has a basic sensitivity (at Earth’s radiating temperature) of about 0.27 °C/(W/m2). That is, a change in radiative forcing of about 4 W/m2 would give around 1°C warming. The second thing to know is that the Earth is not a black body! On the real planet, there are multitudes of feedbacks that affect other greenhouse components (ice alebdo, water vapour, clouds etc.) and so the true issue for climate sensitivity is what these feedbacks amount to.

So here’s the first trick. Ignore all the feedbacks – then you will obviously get to a number that is close to the ‘black body’ calculation. Duh! Any calculation that lumps together water vapour and CO2 is effectively doing this (and if anyone is any doubt about whether water vapour is forcing or a feedback, I’d refer them to this older post).

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