In fact, Karl Popper said nothing at all about ‘climate change’ — what used to be called Anthropogenic Global Warming. The reason is straightforward. He died in 1994, aged 92, before the current fashion of AGW had reached its height. It is easy enough to suppose that he would have said, perhaps, that AGW is there to be falsified, and no one has falsified it yet — well emphatically anyway — so it can be accepted as the ruling theory. I have some sympathy with this approach, but it is I think too glib.
Popper wrote a great deal — 22 books and an unknown number of papers — and he wrote over a wide expanse of human knowledge. In the domain of ‘climate change’ he would be best known for his general perspective on the philosophy of science, in which he proposed that scientific theories could never be proven (proofs are for mathematics) but could be falsified, and that good science occupies itself in trying to falsify hypotheses through observation and experiment. In that way, he said, science advances. He was scathing at what he saw as attempt to postpone such tests, or avoid them, by protecting the original hypothesis. Other philosophers of science, especially Lakatos and Feyerabend, adapted his ideas to their own ends, and Popper’s perspective today is not as dominant in the field as it once was.
Nonetheless, I prefer his simple position about falsifiability to others. I heard him in a seminar in the late 1980s at the ANU, and he was most impressive, but I have not ventured very far into his work. But he is so eminently quotable. Here is a long passage from The Open Society and its Enemies, just an aside really, in a chapter on the sociology of knowledge; but it is so illuminating. I have done some editing, and separated some of the text into numbered paragraphs for the sake of the reader — the original comes in two long paragraphs. The emphases are in the original.
1. Everyone who has an inkling of the history of the natural sciences is aware of the passionate tenacity which characterises many of its quarrels. No amount of political partiality can influence political theories more strongly that the partiality shown by some natural scientists in favour of their intellectual offspring. If scientific objectivity were founded… upon the individual scientist’s impartiality or objectivity, we should have to say goodbye to it…
2. [T]here is no doubt that we are all suffering under own own system of prejudices… that we take many things as self-evident, that we accept them uncritically and even with the naive and cocksure belief that criticism is quite unnecessary; and many scientists are no exception to this rule, even though they may have superficially purged themselves from some of their prejudices in their particular field. [But however hard they try] they could not possibly attain to what we call ‘scientific objectivity’. No, what we usually mean by this term rests on different grounds. It is a matter of scientific method.
3. And, ironically enough, objectivity is closely bound up with the social aspect of scientific method, with the fact that science and scientific objectivity do not (and cannot) result from the attempts of an individual scientist to be ‘objective’ but from the co-operation of many scientists. Scientific objectivity can be described as … what I may term the ‘public character of scientific method’… [It has two important aspects.]
4. First, there is something approaching free criticism. A scientist may offer his theory with the full conviction that it is unassailable. But this will not impress his fellow-scientists and competitors; rather, it challenges them: they know that the scientific attitude means criticizing everything… Second, scientists try to avoid talking at cross-purposes… In order to avoid speaking at cross-purposes, scientists try to express their theories in such a form that they can be tested, i.e. refuted (or else corroborated) by such experience.
I find that section of his work clear and unambiguous, and I have encountered examples of his argument in my working life. If I were to summarise it in terms of my paragraphing, I would present it like this.
Paragraph 1 Once we have become committed to our hypothesis it is very difficult for us to accept criticism, even if we try to be objective about it. (If pushed hard we will build defences around our hypothesis — he says that elsewhere.)
Paragraph 2 We all do this sort of thing, and we will keep doing it, no matter how hard we try to be ‘objective’.
Paragraph 3 What saves us, and allows science to progress, is the co-operation of multitudes of scientists in exposing weaknesses in one’s hypothesis through the scientific method.
Paragraph 4 And that method consists of a hypothesis’s being exposed to experimental and/or observational data. If it survives that exposure, it can present as reliable, at least for the moment. If it doesn’t, it is rejected, however beautiful a hypothesis it is.
How does climate science stand up to all this? Not at all well, it would seem to me. The ruling hypothesis is that carbon dioxide is the control knob for the planet’s atmospheric temperature: the more of it, the hotter the atmosphere, and hotter atmospheres must lead to higher sea-levels, and all manner of other evils. Testing the hypothesis is bedevilled by problems of measurement: the globe is a big place, we don’t really know how much carbon dioxide there was in the air three hundred years ago, and we find it hard to agree on temperature measurements now, let alone those from one hundred years ago.
At the very least there are awkward problems with the ruling hypothesis. On the face of it, and accepting for the moment the reliability of temperature measurements over the last century or so, carbon dioxide has been increasing pretty steadily, but temperature has wobbled around, and there doesn’t appear to be a satisfying explanation for that disjunction. Equilibrium Climate Sensitivity, which is supposed to exist and to multiply the effects of a doubling of CO2 to several degrees of extra warming, has not been found, after thirty years of assertion. The apparent ‘hiatus’ in the present century has been a problem for the hypothesis, for over the past 16 years we do have more or less reliable estimates of both CO2 and temperature. The defenders of the hypothesis have come up with a very large number of explanations, none of which is persuasive, and none of which can be easily tested.
My feeling is that Karl Popper would shake his head at all that, and say that too much effort is going into defending the ruling hypothesis and much too little into testing it properly. Noting that elected governments appear reluctant either to dismiss the hypothesis or to act on its recommendations, he might say that this whole area of science has become highly politicised.
Now I recognise that I might be over-keen to have the ruling hypothesis dismissed, no matter how ‘objective’ I might see myself as. No matter, I am prepared to wait until the hypothesis has been properly tested. I can only add that the longer it takes, the more likely it is that the CO2 control knob theory of climate will be rejected.
Footnote: Those who are interested in reading Popper may find it helpful to be guided by Rafe Champion, a student of the whole Popper oeuvre. You can see his readings and other advice here.