During World War I, French doctors working on the battlefield were often presented with far more wounded soldiers than they had the time or resources to care for. Faced with the stark reality that they would lose patients no matter what they did, these doctors came up with a system of “triage,” letting the most critically wounded die so as to save the most lives.

The time may have come for us to use a similar triage system to save species, according to Terry Root, a Stanford biologist who, along with her fellow authors with the Intergovernmental Panel on Climate Change, won a 2007 Nobel Peace Prize. “If you had told me even five years ago that I would be saying we need to deal with triage, I would tell you you were crazy,” Root says. “But … you can’t save everything.”