Natural gas gas is often described as the cleanest fossil fuel. It produces 25–30% and 40–45% less carbon dioxide per joule delivered than oil and coal respectively, and potentially fewer pollutants than other hydrocarbon fuels. However, in absolute terms, it comprises a substantial percentage of human carbon emissions, and this contribution is projected to grow. According to the IPCC Fourth Assessment Report, in 2004, natural gas produced about 5.3 billion tons a year of emissions, while coal and oil produced 10.6 and 10.2 billion tons respectively. According to an updated version of the Special Report on Emissions Scenario by 2030, natural gas
Natural gas in the United States the oil and the gas are treated separately. Gas flows through a gathering system into a pipeline to a gas processing plant. As of 2014, there were 189,000 miles of interstate natural gas pipelines in the United States Natural gas has a variety of chemical constituents that must be removed or diluted with other gas to achieve consistent pipeline quality. Pipeline gas specifications vary from line to line, but generally the gas must contain no appreciable hydrogen sulfide (which is toxic), less than a few percent carbon dioxide (carbon dioxide reacts with water to form carbonic acid, which is corrosive