The main man-made source of carbon dioxide is the burning of fossil fuels. Industry is the largest source of total gross emissions, and transportation the second. According to the IPCC, if the world is to stabilize greenhouse gases at 1990 atmospheric levels, we must reduce carbon dioxide emissions by over sixty percent, methane by fifteen to twenty percent, and other greenhouse gases between forty and eighty percent. Methane is the second most prevalent anthropogenic greenhouse gas. Sources of methane in the U.S. include landfills, agricultural activities, fossil fuel combustion, coal mining, production and processing of natural gas, and wastewater treatment.
Landfills are the largest single source, comprising almost a third of methane emissions.
Emissions from agricultural activities and oil are the next largest sources of U.S. methane emissions. The U.S. was the fourth nation overall, and the first industrialized nation, to ratify the Framework Convention on Climate Change. Under this treaty, the world's industrialized nations pledged to undertake policies and measures to reduce their emissions of the greenhouse gases that are changing the Earth's climate. Its main goal is to reduce U.S. greenhouse gas emissions to their 1990 levels by the year 2000. Under the Framework Convention treaty , the United States is negotiating legally binding targets for reducing greenhouse gases.