A study of climate history is an essential foundation for climate policy. Earth's history gives us an appreciation of the wide swings in the types of climate that are possible. It informs us of the forces that have generated those fluctuations and have stabilized the planet's temperature at very different levels for long periods of time. It provides estimates of the temperatures associated with much greater or much less planetary ice cover than we have today. And it offers case studies of episodes of climate change that bear an eerie resemblance to scenarios that could characterize our future.

A sense of the limits of our scientific knowledge is also essential. Uncertainties about the science place extra burdens on the design of policy. We cannot merely implement what “science” tells us to do, because the science itself is evolving and controversial. To make wise policy, we need to assess what is known with confidence and what remains highly speculative. Our uncertainty will condition the degree of flexibility we should build into the framework for policy.