Earth has been a snowball and a hothouse at different times in its past. So if the climate changed before humans, how can we be sure we’re responsible for the dramatic warming that’s happening today?
In part it’s because we can clearly show the causal link between carbon dioxide emissions from human activity and the 1.28 degree Celsius (and rising) global temperature increase since preindustrial times.
But paleoclimatologists have also made great strides in understanding the processes that drove climate change in Earth’s past. Here’s a primer on 10 ways climate varies naturally, and how each compares with what’s happening now.