Global Warming Deniers sometimes employ a funny little meta-argument that, I believe, first made an appearance in a 2003 lecture sci-fi writer Michael Crichton gave entitled "Aliens Cause Global Warming". In his lecture, Crichton does not directly challenge the science behind GW claims, nor even the further claim that a scientific consensus exists to the effect that the phenomenon is occurring and is largely anthropogenic. Instead, Crichton tries to argue against the very concept of a "scientific consensus", treating the idea as some kind of post-modern holdover from the decadent 60s. That scientists claim a consensus exists around Global Warming, he holds, actually tells against the research comprising this consensus.
Crichton kicks off his argument as follows:
I want to...talk about this notion of consensus, and the rise of what has been called consensus science. I regard consensus science as an extremely pernicious development that ought to be stopped cold in its tracks. Historically, the claim of consensus has been the first refuge of scoundrels; it is a way to avoid debate by claiming that the matter is already settled. Whenever you hear the consensus of scientists agrees on something or other, reach for your wallet, because you're being had.
Let's be clear: the work of science has nothing whatever to do with consensus. Consensus is the business of politics. Science, on the contrary, requires only one investigator who happens to be right, which means that he or she has results that are verifiable by reference to the real world. In science consensus is irrelevant. What is relevant is reproducible results. The greatest scientists in history are great precisely because they broke with the consensus.
There is no such thing as consensus science. If it's consensus, it isn't science. If it's science, it isn't consensus. Period.
In addition, let me remind you that the track record of the consensus is nothing to be proud of....
Note: Crichton gives several examples at this point of a scientist "breaking the consensus" and being proven right. For the sake of brevity, I will just reproduce one.
Probably every schoolchild notices that South America and Africa seem to fit together rather snugly, and Alfred Wegener proposed, in 1912, that the continents had in fact drifted apart. The consensus sneered at continental drift for fifty years. The theory was most vigorously denied by the great names of geology-until 1961, when it began to seem as if the sea floors were spreading. The result: it took the consensus fifty years to acknowledge what any schoolchild sees.
At this point the obvious counter-argument seems to present itself. Doesn't the example simply show that a scientific consensus can change? The consensus pre Wegener was that the continents were static; by the 1960s the consensus became that there existed a phenomenon called "continental drift".
But if so, by the logic Crichton employs, we should now be doubting the existence of continental drift, for if there is a consensus, "...it isn't science".
And yet Crichton seems to accept these results.
Crichton responds to this argument with a bizarre bit of socio-linguistic theorizing:
Finally, I would remind you to notice where the claim of consensus is invoked. Consensus is invoked only in situations where the science is not solid enough. Nobody says the consensus of scientists agrees that E=mc2. Nobody says the consensus is that the sun is 93 million miles away. It would never occur to anyone to speak that way.
Well, of course, nobody has to say a scientific consensus exists with respect to the distance from earth to the sun, because nobody is stupid enough to question the issue, but does that mean there in fact is not a consensus that the sun is 93 million miles away?
If you look at a standard web definition of a consensus, you find something like:
A consensus implies that debate has taken place, the solution is generally accepted rather than a grudging compromise, and that agreement is deep-rooted enough that it can stand for some time without need to revisit the issue.
...which is surely the situation that holds among scientists with respect to the distance between Earth and the Sun. The agreement to the effect that it is 93,000,000 miles away is deep-rooted enough that they simply don't need to revisit the issue.
Which is to say that Crichton's claim amounts to the following: when scientists have a consensus, they never say so. When they say so, they're almost certainly wrong.
Bizarre as it seems, this thesis is testable. In fact, it can be demonstrated to be false. For instance, here is a brief excerpt from the wiki article on dinosaurs. It concerns the evolutionary link between birds and dinosaurs:
There is an almost universal consensus among paleontologists that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor are related, modern birds are dinosaurs and dinosaurs are, therefore, not extinct
And here is another concerning dinosaur endothermy (warm-bloodedness):
A vigorous debate on the subject of temperature regulation in dinosaurs has been ongoing since the 1960s. Originally, scientists broadly disagreed as to whether dinosaurs were capable of regulating their body temperatures at all. More recently, dinosaur endothermy has become the consensus view, and debate has focused on the mechanisms of temperature regulation.
In both of these cases the consensus view is the consensus view because of the evidence for that view, not in spite of it.