I got into conversation with a taxi driver recently. He asked me what I did for a living, and when I said that I was a chemistry professor, he asked me what I thought about climate change. This man was intelligent, but had no scientific training and he wanted to hear a scientist’s perspective. I told him that unless we change direction quickly we are headed for catastrophic climate breakdown. We talked about the evidence for this, the reliability of climate models and the evidence that supports their predictions. He said he understood what I was saying, but that he hoped we’d find a way through. He said that he felt that there would be some sort of a technological fix that would mean we could carry on as we are. I said that as far as I was aware, there was no evidence at all that we’d be OK if we just carried on as we are.

“But Donald Trump clearly thinks we’ll be OK. He clearly feels differently than you – presumably he has evidence that suggests things will be different.”

“I’m afraid that I don’t know of any evidence that suggests that things will be OK if we carry on as we are”.

“But Trump has lots of clever people to advise him. They wouldn’t be committed to ‘drill baby drill’ unless they thought that everything was going to be OK”.

“There is no evidence at all to suggest that things might be OK if we carry on as we are”.

“None at all?”

“None at all”.

“So why is Trump doing what he is doing?”.

“I can’t tell you what is in Donald Trump’s mind, but I can tell you that I know of know evidence that says we won’t have catastrophic climate breakdown if we follow that course”.

Figure 1. Annual global average temperatures expressed as the difference from pre-industrial conditions based on the 1850-1900 average. Four different data sets are shown – HadCRUT5*, NOAAGlobalTemp*, GISTEMP, and Berkeley Earth* – as well as two reanalyses – ERA5 and JRA-3Q. There is good agreement on the overall evolution of global temperatures and year-to-year variability. From the Met Office Climate Dashboard.

As I said above, the driver was an intelligent man. He was shocked at how emphatic my replies were. I think that a lot of ordinary people somehow feel that it is inconceivable that the president would encourage us to follow a path that would lead inevitably to climate breakdown. I could of course speculate about what the president’s motivations might be. But I’d like to stick to the science. Science is a process of conjecture and refutation: we formulate hypotheses, and we test them. Testing either corroborates or falsifies the hypothesis. Climate models are complicated, and they have error bars, but they are well tested. These models are our hypotheses – rather complicated ones, in the case of global climate, with many parameters. The development of the earth’s climate over the last few decades, during which we have had reliable, detailed measurement data (see Figure 1 for data on global temperature from a number of leading labs, published on the UK Met Office web site) that corroborate predictions of the models; measurements from the EU’s Copernicus satellite show the variation in global sea temperatures and the progressive rise in sea level due to global warming.

On the internet one can find both sock puppets for fossil fuel interests and bumbling amateurs with very little understanding of how to formulate or test a hypothesis, all offering contrary views and bent on proving that they know better than thousands of climatologists and physicists. However, none of them has come up with a competing model that has successfully predicted the development of global climate. The best they can manage is “it’s OK, there isn’t a problem, everything will be OK”. But in Popperian thinking, prediction has a special significance. Climate modellers have predicted the development of global temperatures, and over several decades, the predictions have been tested. All of the data we have support the kind of models championed by the Intergovernmental Panel on Climate Change (IPCC) and not a model in which the earth’s climate is stable. The hypothesis that “the earth’s climate will remain stable if we continue to produce carbon dioxide at our current rate” has been thoroughly falsified. Everything will not be OK if we simply carry on as we are.