"There is concern that human activities are affecting the heat/energy-exchange balance between Earth, the atmosphere, and space, and inducing global climate change, often termed 'global warming.' Human activities, particularly the burning of fossil fuels, have increased atmospheric carbon dioxide (CO2) and other trace greenhouse gases. If these gases continue to accumulate in the atmosphere at current rates, most scientists believe global warming would occur through intensification of Earth's natural heat-trapping 'greenhouse effect.' Possible impacts might be seen as both positive and negative. [...] The United States has indicated it would continue its cabinet-level review of climate change, and would seek new approaches based on voluntary measures and market mechanisms, but no timeframe for a new U.S. proposal has emerged. Other parties continue to express hope that the United States will rejoin international efforts to reduce greenhouse gas emissions."
CRS Issue Brief for Congress, IB89005
U.S. Dept. of State, Foreign Press Centers: http://fpc.state.gov/