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
Low-carbon power entirely renewable sources. Other options, such as nuclear power, produce a comparable amount of carbon dioxide emissions as renewable technologies in total life cycle emissions, but consume non-renewable, but sustainable materials (uranium). The term "low-carbon power" can also include power that continues to utilize the world’s natural resources, such as natural gas and coal, but only when they employ techniques that reduce carbon dioxide emissions from these sources when burning them for fuel, such as the, as of 2012, pilot plants performing Carbon capture and storage. As the single largest emitter of carbon dioxide in the United States, the electric-power