To confront the climate crisis, we need to hedge our bets against the risk of climate change. We must be willing to spend some money now in order reap a larger benefit that will take many decades to deliver. This is similar to the philosophical concept of Pascal’s Wager, where one bets a finite resource for a potentially infinite reward. But estimating how much we should spend now is not easy; attempts to estimate this amount – the “social cost of carbon” – produce a wide range of numbers. We may need to accept that there is going to be radical uncertainty in any numerical estimate. Nevertheless, we can use climate models to quantify the risk of climate change as best we can, while taking into account the different types of uncertainties. Often, risk assessment requires numerical probabilities, but these are not always available for uncertainties associated with climate prediction.