The cumulative Covid-19 death rate per million of the population is nearly 740 in the US, and 760 in the UK, compared with 3 in China and 15 in Japan, according to Johns Hopkins University. Infectious diseases in their initial stages tend to grow at exponential rates. For example, if they double every three days, they will increase 1,000-fold within a month, unless slowed down by social distancing or herd immunity. But human beings struggle to grasp that idea, and instead tend to assume that the number of cases will grow by the same absolute number each day, leading them to underestimate the danger. The effects of climate change also increase exponentially, albeit over a much longer period than a pandemic. Time lags between cause and effect are very lengthy, making interpretation obscure to the public. Externalities are unavoidable, and apply across international borders, making them even harder to address. Human biases leave us systematically underprepared to address serious but re