What simulations of past warm climates tell us about the future

Future increases in atmospheric carbon dioxide due to human activity will lead to a radiative forcing of from 5 to 10 Watts per square meter by the end of this century. The last time Earth experienced this magnitude of forcing was tens of millions of years ago. Results from climate model simulations of deep past warm climates will be presented. I will discuss the relevance of these simulations to future climate change. Emphasis will be on mechanisms that may have been unique to the past and those that may be important for future climate change. I will also discuss the implications warm climates to changes in the biosphere.