About 3 million years ago, carbon dioxide levels were similar to today’s. What other changes might we expect?
Julius T. Csotonyi
Imagine a world where the polar ice sheets are melting, sea level is rising and the atmosphere is stuffed with about 400 parts per million of carbon dioxide. Sound familiar? It should. We’re living it. But the description also matches Earth a little over 3 million years ago, in the middle of the geologic epoch known as the Pliocene.
To understand how our planet might respond as global temperatures rise, scientists are looking to warm periods of the past. These include the steamy worlds of the Cretaceous Period, such as around 90 million years ago, and the boundary of the Paleocene and Eocene epochs, about 56 million years ago.
But to many researchers, the best reference for today’s warming is the more recent Pliocene, which lasted from 5.3 million to 2.6 million years ago. The mid-Pliocene was the last time atmospheric CO2 levels were similar to today’s, trapping heat and raising global