While the world debates how best to reverse the trend of anthropogenic global warming (AGW), scientists continue to refine their data on historical global temperatures. A recent study published in Nature adds to this a high resolution picture of average surface temperatures over the last 24,000 years, since the last glacial maximum. The study reinforces the conclusion that the last century of warming is unprecedented over this time frame, and does not reflect any natural cycle but rather the effects of human forcing.

To construct their map of past temperatures, the researchers combined two methods. They used a dataset of chemical analysis of marine sediments, which are affected by local average temperatures. They combined this with a dataset based on computer-simulated climate models. The idea was to leverage the strengths of each approach to arrive at a map of historical surface temperatures that is more accurate than either method alone.

Of course, no one study is ever the final word, but this reconstruction is in line with other research using independent methods and data. The authors also draw two other main conclusions from their data. There has been a debate about whether or not the last 10,000 years had a small warming trend, and this graph supports that conclusion. Further, the authors conclude that the main driver of the large warming trend starting around 17,000 years ago is the retreat of the glacial ice sheets, but that the main driver of the rapid warming over the last 150 years is increasing green house gases. The rate of this recent warming is also out of proportion to any natural cycle detected in the last 24,000 years.

Those who refuse to accept the overwhelming scientific consensus on AGW will likely not be moved by this new study. It’s easy to find reasons to dismiss data if you are motivated to do so. For AGW, that motivation appears to be solution aversion – concerns about proposed steps to mitigate AGW and its consequences. For the fossil fuel industry, this motivation is obvious. They have massive assets in the ground they want to capitalize on, and will push back against any policy that deprives them of those assets. But they have successfully financed a disinformation campaign and turned it into a political ideology. Now denying AGW is a matter of tribal identity for some.

This denial takes many forms, but they tend to flow into each other. There are “stages” of denial: the Earth is not warming, the Earth is warming but its part of a natural cycle, human activity is causing the warming but it won’t be harmful (and may even be beneficial), human activity is causing warming and it will be bad but there’s nothing we can do about it or need to do about it. The one thing that all these positions have in common is the conclusion that we need not do anything about AGW – solution aversion. In practice deniers tends to flow up and down the list of positions depending on the situation, using a Motte and Bailey defense strategy. They will deny that warming is even happening when they think they can, but otherwise will retreat to more defensible positions when necessary, only to sally forth later to again deny even that warming is happening.

Other strategies employed regularly by deniers is to deny that science denial is even a thing. This is nothing short of gaslighting – what’s happening right in front of your face is not happening, you are just confused. They may accuse you of antisemitism, equating all accusations of science denial with holocaust denial (a non sequitur and poisoning the well strategy). In fact, denialism is a real phenomenon, with a defined set of strategies and logical fallacies. I have been writing about science denial for 25 years, long before AGW denial was a hot topic.

Deniers also have multiple strategies when confronted with the consensus of scientific opinion. If you want to promote a certain belief, it’s inconvenient if the vast majority of scientists say that your belief is wrong based on facts and research. If you yourself are a published and credentialed expert, then you can express a contrary view as science welcomes dissent and minority opinions. You will have to defend yourself, but at least you have the expertise to justify a contrary opinion. But for most people who are not recognized experts, this opposition of a strong scientific consensus is a problem. One strategy is to just deny that the opposing consensus exists. How does a member of the lay public know what the consensus is, unless they regularly talk to lots of scientists in the field? But what if there are multiple studies leading to a consensus on what the consensus is? This is the situation with AGW – there is a strong consensus that it is real and the consequences are potentially very bad.

Then, you can deny the very concept of consensus itself. You have to deliberately misunderstand the concept of consensus, but that apparently is not a problem. Deniers will portray it as “voting on reality”, dogma, or that the notion of consensus does not exist in real science. This is all nonsense – the concept is actually quite simple. What do the majority of science conclude about the state of the evidence on any particular question? If the vast majority conclude the same thing, that’s a consensus. It reflects the evidence and prevailing theories – it is not mere opinion or a vote.

The final refuge of the denier, then, is to deny the very concept of expertise and to attack individual experts or even fields of experts. This requires conspiracy mongering, but that is already common practice among deniers. They can play the shill card, or claim that all the experts are just playing the public for their own benefit, or they are all “liberal elites” or whatever bogeyman is convenient. All they have to do here is create as much doubt and confusion as possible. They don’t need to support a coherent scientific alternative, just throw as much sand in the gears of knowledge as possibly to get the public to throw up their arms in confusion. In recent years some deniers have taking to exploiting FOIA requests and other fishing expeditions to look for anything that can be spun into dirt, to smear experts and cast doubt on the consensus. This strategy works, at least temporarily and within tribes that are already ideologically amenable to the denial.

It’s not a good long term strategy, however. Scientific evidence and logic tends to win out in the long run, and I think we are seeing that with AGW. Again, this is just one study, but it is part of a steady drip of evidence strengthening the consensus on AGW. We are also starting to see some real world effects that are increasingly difficulty to deny. In the end, the denial position does not align with reality, because it is using a pseudoscientific method. It puts the conclusion before logic and evidence and tries to work backwards. This can slow progress and cause confusion, but is not sustainable and does not make any real progress. Unfortunately, as a delay tactic it has been effective, and in the end we will all pay the price for the delay.