As a philosopher, I have nothing to add to the scientific evidence of global warming, but I can tell you how it’s possible to get ourselves to sincerely doubt things, despite abundant evidence to the contrary. I also have suggestions about how to fix this.

To understand how it’s possible to doubt something despite evidence to the contrary, try some thought experiments. Suppose you observe a shopper at the convenience store buying a lottery ticket. You are aware that the probability that he will lose the lottery is astronomically high, typically above 99.99 percent, but it’s hard to get yourself to sincerely say you know this person will lose the lottery. Now imagine your doctor screens you for a disease, and the test comes out negative. But consider the possibility that this result is one of those rare “false negative” cases. Do you really know the result of this particular test is not a false negative?

These scenarios suggest that it’s possible to feel as though you don’t know something even when possessing enormous evidence in its favor. Philosophers call scenarios like these “skeptical pressure” cases, and they arise in mundane, boring cases that have nothing to do with politics or what one wants to be true. In general, a skeptical pressure case is a thought experiment in which the protagonist has good evidence for something that he or she believes, but the reader is reminded that the protagonist could have made a mistake. If the story is set up in the right way, the reader will be tempted to think that the protagonist’s belief isn’t genuine knowledge.

When presented with these thought experiments, some philosophy students conclude that what these examples show is that knowledge requires full-blown certainty. In these skeptical pressure cases, the evidence is overwhelming, but not 100 percent. It’s an attractive idea, but it doesn’t sit well with the fact that we ordinarily say we know lots of things with much lower probability. For example, I know I will be grading student papers this weekend. Although the chance of this happening is high, it is not anything close to 100 percent, since there is always the chance I’ll get sick, or that something more important will come up. In fact, the chance of getting sick and not grading is much higher than the chance of winning the lottery. So how could it be that I know I will be grading and not know that the shopper at the convenience store will lose the lottery?

Philosophers have been studying skeptical pressure intensely for the past 50 years. Although there is no consensus about how it arises, a promising idea defended by the philosopher David Lewis is that skeptical pressure cases often involve focusing on the possibility of error. Once we start worrying and ruminating about this possibility, no matter how far-fetched, something in our brains causes us to doubt. The philosopher Jennifer Nagel aptly calls this type of effect “epistemic anxiety.”