For billions of years the earth's climate has remained stable in the sense that liquid water has always existed. Natural variations have ranged from "snowball earth" to greenhouse planet in the Cretaceous period when no permanent ice existed.

After a relatively long period of stable climatic during the last 10,000 years, humans have now taken control and steer us into a new and warmer climatic age. The exact point, where this is going to take us, will be a result of what we are going to do.