Unfortunately, our models of global warming cannot tell us with a high level of confidence how rapid that change will be and how high the temperatures will rise in 50 or 100 years: difference of a single degree of Celsius translate into very different environmental and economic consequences. If we knew what was coming with certainty we could decide which one of the two main courses of action – gradual adaptation or an all-out effort aimed at emission reduction – is the more rational choice. But we do not, and this means that our production and use of energy, and hence our economic and social well-being, will continue to unfold in a world of profound uncertainty. That, too, is one constant that will not change for decades to come.