Palaeocast has an interesting episode on the Paleocene/Eocene Global Thermal Maximum.   This was a very warm period in earth’s history.  It happened around 56 million years ago.

The Bighorn Basin in Wyoming has been an important area for research into terrestrial ecosystems for decades. The basin formed as part of the uprising of the Rocky Mountains in the west of North America, and sediment from the surrounding mountain ranges was transported into it for millions of years, building up a huge thickness that has fossils from all kinds of life on land preserved within it. Rocks from many different time periods are now exposed in the basin, but a particularly important one is the Paleocene Eocene thermal maximum (PETM) which occurred around 56 million years ago. At this time a huge amount of carbon was released into the atmosphere very quickly, causing a sharp (by geological standards) increase in temperature and dramatic effects on life. Palaeontologists and geologists are particularly interested in studying the PETM as it can potentially give us lots of information about how life and earth systems might respond in the near future to the large quantities of carbon being released into our atmosphere now by humans.