Human activities are yielding rising atmospheric concentrations of greenhouse gases and other gases and particulates which are greatly altering the Earth's land cover. A scientific consensus has emerged that those activities, if allowed to continue unabated, will have extensive, highly uncertain, but potentially serious and costly impacts on regional climates and ocean conditions throughout the world. This book presents an overview of the current understanding of the impacts of climate change in the U.S., emphasising the wide range of uncertainty about the magnitude and timing of those impacts and the implications of that uncertainty for the formulation of effective policy responses.