"There is growing evidence that human activities are affecting the heat/energy exchange balance between Earth, the atmosphere, and space through an increase in 'greenhouse gases.' If these gases continue to accumulate in the atmosphere at current rates, most scientists believe significant global warming would continue to occur through intensification of Earth's natural heat-trapping 'greenhouse effect.' Over the past 100 years, particularly in recent decades, there have been measurable increases in global temperature and sea levels, decreases of sea ice in the Arctic, and melting among the world's continental ice sheets and mountain glaciers. Disagreements focus mainly on the magnitude and rate of change, the severity of estimated warming, and its projected impacts - both positive and negative. Moreover, wide variations of scientific opinion accompany model projections of a warmer world: if these increases in greenhouse gas emissions continue, global average temperature could rise anywhere from 2.7oF to 10.7oF over the next 100 years. Because the U.S. economy is so dependent upon energy, and so much of U.S. and worldwide energy is derived from fossil fuels, options for reducing emissions of carbon dioxide and other greenhouse gases pose major challenges and controversy. This report briefly reviews the status of climate science, international negotiations, and congressional activity focused specifically on climate change."
CRS Report for Congress, RL33602