chained hydrogen and carbon molecules needed to produce liquid petroleum and is only, therefore, a source of natural gas and coal. Gas produced in this way is mostly methane without the natural gas liquids. A final source of natural gas is the anaerobic digestion of near-surface carbon in soil and permafrost by microbes. This biogenic gas is exclusively methane. Natural gas accounted for 29% of USA energy consumption in 2017 (Oil accounted for 38% and coal, 15%. Solar and wind accounted for 3%). The principal drawback of natural gas as an energy source is that it is a gas and can only be moved efficiently by pipeline. Oil and coal, by contrast, can be moved by rail, truck or boat. Liquefied natural gas may be put on specialized cryogenic ships, but liquefaction is a very costly process in money and in energy. So far, uses of natural gas as a transport fuel are limited. The main theoretical benefit of natural gas is that it does not emit nearly as much greenhouse gas as coal when burned. However, over a 20-year period, pure (unburned) methane is 96x as potent as CO2 in causing atmospheric heating 111 (methane doesn’t last very long in the atmosphere, with a mean time of 12 years before it reacts with hydroxyl molecules to turn into CO2 and water). But recent aerial data suggests that the leakage from well-to-power plant is 2.3% (above EPA estimate of 1.4%). The math works out that the current leakage rate, natural gas has HIGHER greenhouse impacts than coal because of these pipeline leaks and operator error/inattention. From a climate perspective, the fugitive methane emissions from operator carelessness can (and must) be remedied. The other big advantage is power plants using natural gas are fully dispatchable – e.g. can be immediately turned on or off. Even other “baseload,” like coal and nuclear, don’t have that advantage and need hours/or days to transition from off to on. (This will increasingly matter as the percent of electricity from intermittent sources like solar and wind grows). Unlike oil, which many expect to decline from all-time maximum production levels in the coming decade, we continue to see frequent discoveries of new gas fields – especially in Asia – implying human use of natural gas could still increase for many decades.
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