This file includes ONLY the Executive Summary of this study conducted by the Global Change Research Program. For the entire report, visit the USGCRP site.

Observations show that warming of the climate is unequivocal. The global warming observed over the past 50 years is due primarily to human-induced emissions of heat-trapping gases. These emissions come mainly from the burning of fossil fuels (coal, oil, and gas), with important contributions from the clearing of forests, agricultural practices, and other activities.