In 2006, the United States was finally surpassed as the world's number one polluter by China, but the overall level of United States emissions of greenhouses gases still represented around 20% of the world's total. This is viewed as a disproportionate share by many critics, who have suggested that the United States needs to lower its emissions levels. The United States government agrees, and has embarked on a number of initiatives which are aimed at reducing United States emissions.
Emissions of greenhouse gases are often expressed in terms of their potential to contribute to global warming, measured in millions of metric tons of carbon dioxide equivalent (MMTCO2e), using carbon dioxide as a benchmark. According to the United States Environmental Protective Agency (EPA), in 2007, the United States emissions in total were 7,282.4 MMTCO2e. This included 6,021 million metric tons of carbon dioxide itself, along with 699.9 MMTCO2e of methane, 383.9 MMTCO2e of nitrogen oxide, and 176.9 MMTCO2e of PFCs, HFCs, and sulfur hexaflouride.
United States emissions of greenhouses gases come from a number of sources, including electricity generation, industry, and operation of vehicles which run on fossil fuels. When looking at United States emissions, many researchers break the emissions down by origin to identify areas which could be improved, and they may also look at emissions by region. California, for example, has huge electricity demands, but it is not among the highest polluters when it comes to electricity generation, reflecting the fact that the state has tougher clean air standards which have forced power plants to cut emissions.
The United States has set a number of target goals which are designed to decrease overall emissions. These goals usually peg emissions to the gross domestic product of the United States. This is designed to allow the country room for economic growth while also expressing concern about the level of United States emissions. The nation's production of emissions has dropped since such target goals began to be set, suggesting that they are effective.
A number of tools can be used to reduce emissions, including installing better filtration and trapping systems, improving efficiency, reducing demand for energy, and using alternative sources of energy which do not generate as many greenhouse gases. A combination of all of these methods is the most effective way to reduce United States emissions, and it encourages participation in emissions goals by every American, as people can impact emissions in many ways, ranging from installing energy efficient appliances at home to modernizing a power plant.
