The fossil fuels that humanity burns today will be a death sentence for many lives tomorrow. A recent review of 180 articles on human mortality climate changes has settled on a deeply worrying number. Over the next century or so, conservative estimates suggest that a billion people, perhaps more, could die as a result of climate disasters. Like most predictions for the future, this one is based on several assumptions. One is a rough rule called the “1,000-ton rule.” This framework says that for every thousand tons of carbon that humanity burns, it indirectly condemns a future human to death. If the world reaches temperatures 2°C above the global pre-industrial average, which we are well on track to do in the coming decades, then that’s a lot of lives lost. For every 0.1°C of warming from now on, the world could suffer about 100 million deaths. (CARLY CASSELLA)