nature.net 



Gas Trap 



By Robert Anderson 



The steady blue flame glowing be- 

 neath my pancake griddle is, for 

 the most part, burning methane. A sim- 

 ple molecule with four hydrogen atoms 

 bonded to a central carbon (CH 4 ), 

 methane is a clear, odorless gas. Al- 

 though it cooks our comfort food and 

 is a vital source of energy, methane also 

 has a dark side. It is a powerful green- 

 house gas, trapping twenty times as 

 much heat in the atmosphere as a sim- 

 ilar volume of carbon dioxide. 



The real worry is the methane now 

 trapped in ice. At low temperatures 

 (around thirty-two degrees Fahrenheit) 

 and moderate pressures (about thirty at- 

 mospheres), methane and water form 

 an ice called methane hydrate. Rela- 

 tively unknown until the 1970s, most 

 methane hydrate is locked up in sedi- 

 ments alons; continental shelves. A 



smaller amount is buried in Arctic per- 

 mafrost. Together, those deposits hold 

 twice as much carbon as all the Earth's 

 reserves of coal, oil, and natural gas 

 combined. If even a small percentage 

 of that methane hydrate melts, it could 

 dramatically increase global warming. 



At the National Oceanic and Atmo- 

 spheric Administration's "Ocean Ex- 

 plorer" Web site (oceanexplorer.noaa. 

 gov/explorations/deepeast01 /background/ 

 beneath/beneath. html), Peter A. Rona, 

 a marine geologist at Rutgers Univer- 

 sity in New Brunswick, New Jersey, 

 conducts a virtual tour to the depths 

 of the eastern Atlantic. There, as he 

 shows the viewer, are vast reserves of 

 methane hydrate. At the bottom of the 

 Web page is a diagram comparing the 

 simple lattice of ordinary ice with the 

 more complex one of methane hy- 

 drate. The methane molecules in the 

 complex ice are locked inside "cages" 

 of frozen water. 



Methane hydrate does have a good 

 side. Entire communities of deep-sea 



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The science and ethic 



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creatures have evolved the means 

 to thrive on its energy. Texas A & M 

 University's Web page "Lair of the 'Ice 

 Worm' " (www-ocean.tamu.edu/Quarter 

 deck/QD5.3/macdonald.html) describes a 

 colony of polychaete worms whose 

 home is a hydrocarbon seep at the bot- 

 tom of the Gulf of Mexico. 



If investigators figure out how to tap 

 methane hydrate safely, the deposits 

 may help meet humanity's insatiable 

 demand for fossil fuels. Listen to "Min- 

 ing Methane" at www.cbc.ca/quirks/ 

 archives/03-04/jan03.html to hear Scott 

 Dallimore, a geotechnical engineer at 

 the Geological Survey of Canada, de- 

 scribe his team's exploration of hydrate 

 deposits in the Arctic. For a world map 

 of known methane hydrate deposits, go 

 to walrus.wr.usgs.gov/globalhydrate/ and 

 choose the poster at the left in a format 

 for either screen-viewing or printing. 



The big fear of many climatologists 

 is that some poorly understood 

 part of Earth's climate system, pushed 

 to a tipping point by human emissions, 

 might trigger a runaway greenhouse ef- 

 fect. Perhaps the most ominous clues 

 to the threat posed by methane hydrate 

 come from the distant past. According 

 to a NASA news item (earthobservatory. 

 nasa.gov/Newsroom/NasaNews/2001/2001 

 12106303.html), 55 million years ago a 

 large release of the frozen seafloor gas 

 heated the Earth by thirteen degrees E 

 Gavin A. Schmidt, a NASA climatol- 

 ogist, explains how ratios of isotopes 

 of carbon suggest that methane hydrate 

 was to blame for that dramatic warm- 

 ing (www.giss.nasa.gov/research/briefs/ 

 schmidt_02/). 



The most chilling scenario of all, 

 however, comes from the end of the 

 Permian period, when Earth under- 

 went its largest mass extinction. Dan 

 Dorritie, a paleontologist in California, 

 regularly updates his online book on 

 the role the he, among others, thinks 

 methane hydrate played in that horren- 

 dous event (www.killerinourmidst.com/). 

 Dorritie warns, it could happen again. 



Robert Andersos is a freelance science 

 writer living in Los Angeles. 



62 



NATURAL HISTORY May 2006 



