USGS scientists reported at a meeting of the American Chemical Society this week that huge sub-sea reserves of frozen natural gas, if economically recoverable, could serve as a bridge from todayâ''s fossil-fuel-driven world to a low-carbon future. Tim Collett of the U.S. Geologic Survey delivered findings of a November survey that estimated there are 85 trillion cubic feet of gas hydrates or cathrates stored in Alaskaâ''s North Slope alone, enough to heat 100 million homes for ten years. He said itâ''s been shown that itâ''s technically possible to recover the gas, though it remains to be determined at what costs.
Clathrates form when decomposing organic matter mixes with water at high pressures and low temperatures. In 1982, said Collett, the research vessel Glomar Explorer retrieved a meter-long sample of gas hydrate off the coast of Guatemala, prompting further exploration and the enactment in 2000 of the U.S. Methane Hydrate Research and Development Act.
Because natural gas is a fossil fuel, itâ''s not always appreciated that itâ''s a relatively green source of energy. By comparison with coal, per unit electricity produced, natural gas emits between one third and one half as much carbon dioxide. The implications, if huge quantities of gas hydrates could be economically recovered, are immense. To take the United States as the subject of a thought experiment: since coal accounts for half of the countryâ''s electricity and a third of its greenhouse gas emissions, if the entire fleet of coal plants were replaced by gas turbines, the effect would be to reduce U.S. carbon emissions by a sixth or more.
In a video press conference at the ACS meeting, Collett and colleagues described how cathrates were discovered in the laboratory in the nineteenth century and then in nature a century later. (To find the conference, scroll down to ACS Liveâ''s Video Clips and select the fourth screen from left in the second row of screens.) In the last decades itâ''s been established that catrates are available in huge quantities under the worldâ''s oceans, but typically at great depths. Assessment of their recoverability therefore requires a large international effort, but if economic exploitation proves feasible, they could start contributing significantly to the worldâ''s energy supplies by 2015, the USGS scientists guess.