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
Unconventional oil about some of the chemicals mixing with ground water (either as runoff or through seeping). There are processes either in use or under development to help mitigate some of these environmental concerns. The conversion of coal or natural gas into oil generates large amounts of carbon dioxide in addition to all the impacts of gaining these resources to begin with. However, placing plants in key areas can reduce the effective emissions due to pumping the carbon dioxide into oil beds or coal beds to enhance the recovery of oil and methane. Carbon dioxide is a greenhouse gas, so the increased