Among people who reject the scientific consensus about the fact of climate change and its causes, much is made of the fallibility and corruptibility of scientists, on the one hand, and of the consensus being far from complete, on the other. The scientists can't win. If there is a consensus, that shows their position is unscientific, because consensus is allegedly "anathema" in science. If there is disagreement, that shows we can ignore or explain away any claim that science supports the alleged consensus.
The way out of this bind is to look more closely at what is going on in the science of climatology, what are the issues about which there is disagreement and what is the basis of such disagreements. I hasten to add that I am not a scientist but a philosopher of science who has spent a lifetime studying the history and practice of science.
Some of the dissent from the consensus comes from within climatology. I'll look at that later. It is not uncommon to find people from other branches of science who reject the claim that the consensus about climate change is scientific. There is hardly any dissent about evolution among biologists, but it is not hard to find chemists, for example, who reject evolution as scientifically dubious because if cannot be replicated under laboratory conditions. They know from experience that even the most plausible hypotheses can prove wrong when rigorously tested in the lab.
In particular, they have no use for computer models such as atmospheric scientist have to work with. They don't engage with that enterprise. Computer models, they say, are too easily rigged to get the result one wants. They insist that carbon dioxide alone does not fully explain global warming. Nobody in the business says that it does. What climatologist's claim is that it is the key factor in a complex of interacting forces. Climatology is a matter of mastering the pattern of those interactions, and quantifying as precisely as possible the contribution of all the relevant factors to the process.
A good scientific model of a complex process model displays the kinds of factors that may be relevant and leaves a lot of slots in the equations for each that need to be filled in before any clear picture can emerge. It is a bit like an array of dots that can be linked in various ways to form different pictures. The soundness of the picture that emerges depends on there being good grounds for deciding in each case what dots are linked to what others. The evidence is always very specific to the particular forces involved. Some may be a matter of straight physical measurement, like determining the rate at which the Arctic ice cover is shrinking. Others will involve complex biochemical processes, like the differential absorption of carbon dioxide by various organisms. Others involve radiation of various kinds and various ways in which these are absorbed or reflected by different kinds of bodies.
Nobody is competent to evaluate results of measurements in all of the different disciplines involved. There are thousands of people working independently of each other in many different areas, and the specific results they come up with are in each case evaluated by their peers who work in that specific area. In fact most of these inquiries are not commissioned with a view to their relevance to some view of the nature of climate change, but for much more specific purposes. Oil companies, for example, have a strong interest in the shrinkage of Arctic ice, because it is very relevant to exploiting oil deposits in that area. Agricultural scientists are very interested in the absorption of carbon dioxide by organisms. Marine biologists want to know how it gets absorbed into the oceans and how that affects marine life.
The IPCC itself does not commission research. It attempts to put together all that independently generated information in order to get the big picture.
Of course, it cannot guarantee that the picture it draws is entirely correct, no matter how closely it fits the known data. Some people will feel that one or other aspect of the complex has not been sufficiently investigated or given sufficient weight. It is always just possible that there is some completely unrecognized factor that could change the picture radically. But the consensus is that on present evidence the way forward lies in closer study of a host of processes about which we already know a great deal. The picture may need to be clarified in many respects, but it is most unlikely it will change significantly overall. But the picture is very general. Climatology is as far from being able to predict particular hurricanes as vulcanology is from predicting the next eruption.
Computer models have an enormous advantage over models that depended on human calculations. Because they are so fast, they enable us to calculate very precisely just what difference it would make if certain measurements were inaccurate by some particular margin. Doing that across the whole range of factors involved gives a very good means of determining just how vulnerable the big picture is to better data. Scientists who have done such investigations seem to agree that it is very robust. However, it involves very special mathematical expertise that even most scientists lack. So we have to accept or reject the expert opinion on the results of that sort of calculation on trust, or distrust. But the general assessment of scientists is that, in any case, the fit between the picture and the facts is very compelling.
In any area of science it occasionally happens that some very eminent scientist adopts a position that is contrary to the consensus in a matter that is closely connected with their great achievements. Einstein on quantum mechanics, Linus Pauling on vitamin C. I know of one prominent Australian climatologist who thought that a process he had identified would halt the advance of climate change. As I understand it, it involved postulating that warming would give rise to a type of cloud cover that would reduce the amount of radiation reaching the surface of the earth and halt global warming. I understand that it was rejected because of several assumptions it involved. In particular, it would only work if the increased water vapour in the atmosphere went into increasing the area of cloud cover. In fact, studies of the dynamics of cloud formation showed that it went into increasing the mass of a few intense cloud systems, leading to dramatically increased rainfall in some areas and drought in others. But he always felt that his theory was unfairly rejected.
Climate change is so very contentious because dealing with it has such unpalatable consequences for so many important interests and so congenial to others. In arriving at a balanced view of the science of the matter it is most important to understand how that science works in practice. The idea that the broad consensus among scientists is just a matter of ideology, or competition for research funds is utterly implausible, however strong ideological and self interested considerations are informing public opinion.
These very complex interactions can only be understood in terms of models that are in their general form uncontroversial, but inevitably to some degree simplified, leaving margins of room for disagreement and improvement. They need constantly to be refined and revised in the light of more detailed and precisely quantified data and a more precise understanding of the interactions between the various factors involved. That is an ongoing task that will never be completed. There will always be dispute about particular claims. But the consensus about the general pattern the in results so far is agreed to be well based among those who know what they are talking about. Such consensus, far from being anathema is what science establishes. It is also the indispensable ground for constructive disagreement, in which there is fruitful disagreement precisely because that disagreement is based on a great deal of agreement about what needs to be done to settle the disagreement. This is not a peculiarity of climatology. The same apples in genetics and indeed biology generally, anywhere in fact, where interrelating a complex of factors is involved. Science is rarely like observing reactions in a test tube.