Sources and Sinks: What drives long-term climatic trends?

Source: Science Daily

For the entire history of our species, humans have lived on a planet capped by a chunk of ice at each pole. But Earth has been ice-free for about 75 percent of the time since complex life first appeared. This variation in background climate, between partly glaciated and ice-free, has puzzled geologists for decades.

https://www.sciencedaily.com/releases/2019/03/190314192549.htm