As the international community ponders the potential course of future climate changes and their impacts, studies of past climatic changes and their environmental effects provide a way to understand the processes involved in environmental change, the interactions among elements of the ocean-atmosphere-land surface system, and the rates and amplitudes of natural climatic variability. Paleoclimatic studies provide direct evidence of how the climate system changes through time, including its responses to unprecedented (in the instrumental record) changes in its controls. The paleoclimatic record also provides a laboratory for testing the ability of numerical models to simulate conditions different from the current climate.