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
South African gas-electric locomotive experiment. Combustion gases, rich in carbon monoxide and known variously as water gas, producer gas and mond gas, are generated by passing air and steam through some kind of red-hot burning carbonaceous fuel, usually coal. The gas generator consists of a combustion portion, where the fuel is initially burned to generate the required steam. The steam is then blown through this same burning fuel, taking air with it, and the producer gas is then liberated as a by-product of this combustion. Ordinarily, burning produces carbon dioxide, but by forcing steam through the burn a certain amount of incomplete combustion is