For the first time, vast amounts of data on the economic and social effects of climate change are becoming available, and so is the computational power to make sense of it. Taking this opportunity to compute a precise social cost of carbon could help us decide how much to invest and which problems to tackle first. “It is the single most important number in the global economy,” says Solomon Hsiang, Lab co-director and a climate policy expert at Berkeley. “Getting it right is incredibly important. But right now, we have almost no idea what it is.” This article delves into our progress on calculating the mortality costs of climate change and includes an interview with Lab co-director Michael Greenstone.