“There is a cautionary tale buried in Earth’s past. Some 56 million years ago, about 10 million years after the dinosaurs went extinct, a massive amount of carbon surged into the atmosphere, triggering a rise in temperature of 5°C. Scientists often look to the so-called Paleocene-Eocene thermal maximum (PETM) as an analog for today’s rising temperatures, because the magnitude of that ancient carbon injection is thought to be comparable to what humans will release if fossil fuel emissions continue unabated for a few more centuries.”