Synthetic natural gas—natural gas produced from coal, oil or biofuels—generates carbon dioxide when burned for fuel just like traditionally produced natural gas. But in experiments, synthetic natural gas has been made by harnessing carbon from the CO2 in the air and combining it with hydrogen, thus creating the possibility of a carbon-neutral fuel. When burned, synthetic natural gas produced this way would not add to atmospheric CO2, only return what it took away. Natural gas is another name for methane, a molecule with one carbon atom and four hydrogen atoms.
Today, the quantity of CO2 emitted from burning synthetic natural gas varies depending on its source material. Burning coal- or oil-derived synthetic natural gas generates more CO2 than simply burning coal or oil. Less often, synthetic natural gas is produced using renewable electricity sources, lowering its carbon footprint.