The situation is not as certain as some headlines would have us believe. Yet, rather than being an excuse to do nothing, this uncertainty challenges us to choose our policies with even greater shrewdness and care. Fahrenheit by the middle of the next century. These models are only approximations of the real atmosphere, but their results, while uncertain, must be taken seriously. The climatic response judged by actual temperature read- ings from around the world during the past century is less conclusive.
Some temperature records for example, for the United States reveal no evidence of change.
Most estimates of the social and economic consequences of global warming are based on scenarios of the future course of climate change and models of economic development. These scenarios can only provide information about the range of possibilities and not predictions of how climate changes will affect agriculture, water resources or ecological systems. In other words, despite all the headlines, what we have is an inverted pyramid of knowledge, a growing mass of proposals for action balanced upon a handful of real facts. At the very least, we need to invest immediately in improving the in- formation base. We also should adopt policies that will ease the situation without foreclosing our future options if projections turn out to be incorrect.