at The Register

This piece originally had a much longer section summing up the state of climate “science” – which the CRU leak has verified. The peculiar nature of the problem is why anecdote and modelling play such an important part in the persuasion business.

Scientific theories fall by the wayside when they fail to be the give us the most convincing explanation of the evidence. The onus is therefore on the supporters of the theory to make the demonstrations, not for opponents to ‘trump’ them, and come up with one better. Otherwise we’d still be discussing the distribution of phlogiston, or the particular qualities of ectoplasm.

Prior to 1980, the dominant factor influencing modulations in climate was thought to be the sun. This makes sense, since our primary energy source (unless you happen to live by a volcano vent) is the sun. If the current vogue for greenhouse gases loses favour, the result will not be a dangerous unstable rip in the fabric of space time. It’s simply likely that the consensus will, in the absence of a more compelling explanation, revert to solar influences.

(Ironically Hubert Lamb, the father of climatology who left the Met Office to found CRU in 1972, remained sceptical of the greenhouse gas theory until the end).

Now every scientific challenges is unique, but the manmade global warming hypothesis poses several specific problems for even the most honest scientist. The real battleground is over aspects of the ‘energy budget’ model – and convincing people means overcoming a number of challenges. The theory posits that small increases in CO2 concentrations (advocates prefer the phrase ‘well-mixed greenhouse gases’) have significant amplification effects. It’s accepted that a doubling of CO2 introduces very little warmth into the system – less than a degree centigrade, which is quite toasty and leaves us someway short of Thermageddon. Increasing the CO2 concentration doesn’t make an appreciable difference; since absorption is logarithmic, it doesn’t matter after a certain point.

So positive feedbacks play a central role in the hypothesis, which suggests that with more clouds, more energy is ‘trapped’, permafrost melts, methane is released, and so on, all increasing temperatures further. Global Warming theory rests on these strong positive feedbacks. If the earth absorbs larger amounts of CO2 than predicted – then the theory fails. If the earth radiates more out to space, then it fails. If the negative feedbacks outweigh the positive feedbacks, then the theory fails. As you may tell by now, demonstrating that greenhouse gases play some kind of role in the climate is not difficult. Demonstrating that they play the dominant role is.

Additionally, and to the perennial amazement of newcomers to the field, there is no ‘fingerprint’ or telltale signal that anthropogenically produced gases are the primary forcing factor. A few candidates have briefly starred in the role – C-14 isotopes, or signs of a ‘hotspot’ under the stratosphere – but these are rarely cited now. The ‘smoking pistols’ have proved to be ambiguous, or missing in action. With the human component just a small part (5 per cent) of CO2, and CO2 a small (5 per cent) part of the overall greenhouse gas mix, the challenge is clear.

Hence the increasing dependence, since 1980, of a range of anecdotal evidence, and computer modelling. In instances where simple empirical tests are sufficient to provide a theory, neither is needed. But science has now moved into what critics call a ‘post modern’ phase. In 2001, the IPCC published its Third Assessment Report and observed:

“Our knowledge about the processes, and feedback mechanisms determining them, must be significantly improved in order to extract early signs of such changes from model simulations and observations.”

So, while expressing quite frankly the state of the science, the IPCC was giving increasing weight to computer models as it was to observations. Modelling was beginning to eclipse empirical evidence.

So reasonable doubt exists whether something as significant as clouds are a positive or negative feedback. The Fourth Annual Assessment acknowledged that the “Level of scientific understandings” of non-Greenhouse forcings was low. That was charitable, the science hasn’t really been done yet.

Now it’s clear from the CRU exchanges – particularly between the Wigley and Trenberth “Where did the Warming go?” dialog – that the energy budget isn’t scientifically understood at all.

Not Proven is a reasonable verdict.