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Climate Science & Falsifiability

Richard Lawson shows how Karl Popper can help settle the climate debate.

Policymakers worldwide face a major headache relating to energy strategy. On the one hand, most climate scientists are warning that we must make a radical change away from reliance on carbon-based fossil fuels in order to avoid a catastrophic long-term change in global climate. On the other hand, the politicians are intensively lobbied by, and sometimes financed by, immensely wealthy and powerful fossil fuel corporations. Moreover, many popular newspapers and influential commentators are sceptical of prevailing climate science, and there is an active and noisy campaign against climate theory by contrarians in the social media. The electorate is of two minds; they do not like the apparently abnormal kinds of weather they are experiencing, but neither do they like the idea of the higher fuel bills or taxes that may be forced by decarbonisation. Small wonder that politicians have gone quiet on climate change.

Philosophers may not find this a particularly attractive arena to step into, but we have a moral duty to help unlock the truth about climate change if we can. And we do possess a key, in the form of the principle of falsifiability set out by Karl Popper in his book The Logic of Scientific Discovery (1934).

A black swan
Photo © Grant Bartley 2014

Earlier, logical positivists such as A.J. Ayer had argued that for a proposition to be meaningful, it must in principle be capable of proof (‘verification’). But Popper argued that the hallmark of a genuinely scientific proposition is not that it can be verified (because no number of observations can conclusively prove a hypothesis), but that the proposition can in principle be disproved (‘falsified’). For example, the proposition ‘All swans are white’ cannot be proved no matter how many swans you see; but it can be disproved by seeing just one black swan.

Popper & Kuhn

Is Popper still popular? W.V.O. Quine was happy to endorse falsification, although he modified the principle to make allowances for the quality of data purporting to overthrow a hypothesis, and to allow that new findings might simply force a modification of a hypothesis rather than its absolute refutation – with which idea Imre Lakatos agreed. But Thomas Kuhn in The Structure of Scientific Revolutions (1962) instead described the historic processes science follows: a consensus position or paradigm prevails in some area of science, but will eventually be overthrown by some radically new paradigm.

Both sides of the climate debate have availed themselves of Kuhn’s ideas. Climate contrarians have tried to present themselves as overthrowers of the prevailing climate science paradigm. However, there is more to being a Galileo than merely objecting to the prevailing consensus. It is necessary to possess a convincing and powerful alternative theory, and with the contrarians this is not the case, as we will see.

Indeed, the prevailing climate science might itself be characterised as having overthrown an old way of thinking. Soon after Svante Arrhenius first raised the possibility of an anthropogenically-enhanced greenhouse effect in 1896, Anders Angstrom argued on the basis of a simple laboratory experiment that the effect of carbon dioxide in absorbing infra red energy was very limited. Angstrom’s view prevailed until the 1960s, when it became understood that convection processes within the atmosphere means that his argument does not hold up. So it can be said that the contrarians represent the old paradigm; and indeed, Angstrom’s argument is still a core talking point in the contrarian community.

Not that this has much to do with the validity or otherwise of either side’s argument. In essence, Kuhn’s theory has more to do with the sociology of science than with its content. However, Kuhn did emphasise criteria for choosing one scientific theory over another: accuracy, consistency, broad scope, simplicity, and fruitfulness. Popperian falsifiability is implied by Kuhn’s first criterion – accuracy.

It is of course only too true that social and psychological factors influence what scientists accept and believe, but this is peripheral to the core of science. It’s what scientists might call ‘noise’. The central matter, the ‘signal’, is our changing understanding of objective reality, which scientists encounter as data, and data is still what they have to deal with. We can conclude that the refutation of theories through contrary data remains at the heart of the scientific method.

The Paradox of Science

Karl Popper (1902-1994)

Popper’s falsifiability principle implies that, contrary to popular misunderstanding, there is no such thing as scientific ‘proof’. The best status that even the best scientific theory can attain is ‘not-yet-disproven’. Even the most durable and revered laws, such as Newton’s laws of motion, may find extreme conditions where they no longer apply. (This does not necessarily mean that the old law is completely overthrown, but rather that its area of application becomes circumscribed.)

This absence of final, definitive proof creates a paradox: science, which we rightly regard as the most certain form of knowledge of the world, exists in a continuous state of uncertainty. In their daily lives scientists are perfectly happy with this uncertainty, not least because each new research paper can truthfully be concluded “More research is needed” – hopefully ensuring a continued supply of funding, and certainly ensuring a continued arena in which they can exercise their curiosity.

The paradox of science can be exploited in the media by opponents of any scientific case, who are able to challenge unwelcome scientific knowledge by saying, “Prove it to me! There you are, you see, you cannot!” The scientist can put forward his evidence; but unfortunately most scientists are trained to be meticulous, and meticulous exposition does not sit easily with the standard two minute popular media discussion.

This then is the predicament in which climate scientists find themselves. They can put forward the evidence, but they cannot force their audience to agree with them. They can point to the fact that carbon dioxide is a greenhouse gas, that its levels in the atmosphere have risen by 40% since the Industrial Revolution, and that we can only account for the recent rise in global temperatures by including the enhanced greenhouse effect alongside known natural factors such as solar variability and ocean currents. They can point to the observed patterns of warming as consistent with warming due to greenhouse gases in contrast to other possible causes of warming. But in the end, the reasoning is inductive, not deductive. It is not proof. To be persuaded, the listener has to recognise a pattern that satisfies a number of questions and agrees with a large number of different lines of evidence. But in the end, no person can be compelled to make an inductive judgement that he or she does not wish to make. A creationist cannot be compelled to believe the evidence of evolution, for example.

This leaves climatologists with a problem. They can make a coherent and reasonable case, presenting the facts to decision-makers. But the decision-makers can also imagine the angry cries of the climate contrarians, and the sound of strife frightens them. They ask the scientists for proof, and all the scientists can say is that further research will narrow down the uncertainties. The only way for the politician to stay in his comfort zone is by deferring the decision to act against carbon-based energy – thus allowing the situation to get worse, forcing the next set of decision-makers to face even more difficult decisions. So the controversy rolls on, with the machinery of climate contrarianism every week putting forward another question to create doubt in the minds of the public, journalists and politicians. A few climatologists and activists devote their free time to answering them, but it is like fighting a Hydra: answer one question, and two more spring up to take its place.

Disproving the Doubters

Is this how it has to be? Can a handful of dissidents, using the megaphone of mass media, sustain inaction on a process of global warming that might well end in disaster for the human species?

Philosophy has revealed the means to resolve this problem. Science may not do proof, but it certainly does do disproof. So although it may not be possible for climatologists to prove their case conclusively, it is possible to look at the contrary hypothesis and refute it. And the contrarians do have a hypothesis: it is that man-made carbon dioxide will not have a severe effect on global climate. This angle transforms the debate into a question about the degree to which the global climate will change given the known increase in greenhouse gases.

There is no reasonable doubt that, ignoring feedback mechanisms, a doubling of carbon dioxide will raise the planet’s surface temperature by about 1.2°C, because this fact is derived from calculations based on universally accepted textbook physics, and is accepted by climatologists and reasonable contrarians alike. The real debate is about climate sensitivity – or what will result from this 1.2°C rise. The Earth’s climate is a complex system of interrelated energy flows, and any warming will result in an array of changes in the system. Most of these changes provide positive feedbacks – that is, they will further increase the initial warming. A number of different lines of evidence drawing from known or deduced changes in global temperature, recent and palaeological, all converge on an eventual temperature rise of between 1.5-4.5°C, with the most likely value being 3°C. Against this, classical climate contrarians put forward a value of 0.5-1°C as their figure for the final temperature increase resulting from a doubling of atmospheric carbon dioxide concentrations. This is their hypothesis; and it is refutable through measuring and calculating the known positive feedbacks – increase in atmospheric water vapour, changes in ice and snow albedo (reflectivity), changes in vegetation, and from secondary releases of carbon dioxide and methane from soil and ocean. The main negative feedbacks (temperature reducers) are a change in heat distribution in the atmosphere, which can be calculated as slightly reducing the positive water vapour feedback, and an increase in total energy radiation from the warming Earth (a feedback which probably sets a limit to extreme planetary overheating). Several attempts have been made by sceptical climate scientists to substantiate their 0.5-1°C warming hypothesis, but each of these has ended in failure. Contrarian scientists placed their faith in clouds to provide a strong negative feedback, for instance, but recently, measurements by Andrew Dessler have shown that the net effect of clouds is more positive than negative (see Science, Vol.330, 10 December 2010).

Perhaps as a result of realising the unsustainability of the idea of ultra-low climate sensitivity, a small sub-set of climate sceptics has emerged recently, the ‘lukewarmers’, who argue for a figure somewhere below that of the consensus view but above that of the classical contrarians. However, given that their evidence base is much smaller than the evidence for higher climate sensitivity, this group is in a very weak position to claim that there is no need decarbonise the global energy supply.

In conclusion, despite the complexity and ongoing uncertainty in understanding the future effects of greenhouse gases on the climate system, one thing is certain: the hypothesis that the effect of carbon dioxide and other greenhouse gases is trivial and warrants no action simply does not hold up. It does not match the facts. It has been refuted. Journalists may not be able to understand science or the philosophy of science to any great depth, but they can understand the concept of ‘disproven’, and climate scientists can indeed disprove the contrarian hypothesis that greenhouse gases will have no significant effect on the global climate.

Richard Lawson is a retired general practitioner and psychiatrist, a blogger, and a veteran environmental activist.