Evidence links methane release to climate change

What do a species explosion, global warming and a possible partial solution to the energy crisis have in common? The answer is a crystal resembling ice, but with many different properties. Placed on a desktop, it fizzes and disappears within minutes leaving a puddle of water behind. Touch a match to the crystal and it burns.

The crystal is called methane hydrate and is an example of a clathrate, a material formed when a gas molecule is trapped within a cage formed by crystalline water or ice. Analysis shows the composition to be one molecule of methane, the major component of natural gas, in combination with six molecules of water. Methane hydrates are not a new discovery, they have plagued oil exploration by clogging drill pipes since the 1930s. It has been only in the past decade, however, that estimates have surfaced of the vast quantities of hydrates locked in the ocean floor, making them more than a curiosity and nuisance.

About 55 million years ago, the planet underwent an evolutionary population explosion that saw the appearance of many mammalian species, such as horses, cows, apes and our own ancestors. Geological evidence shows that this was in conjunction with, and likely due to, a rapid global warming, but what triggered the warming?

Researchers reporting in the Feb. 28, 1997, issue of Science attributed it to a “methane burp” that took place when submarine landslides released huge quantities of methane, a greenhouse gas, into the atmosphere. Richard Kerr, writing in the Nov. 19, 1999, issue of Science, quotes Australian paleooceanographer Gerald Dickens as estimating the release at being more than one trillion tons. Now a paper in the same issue of Science has provided the “methane burp” hypothesis with supporting evidence.

Paleooceanographer Miriam Katz of Rutgers University has made a study of sediment layers buried a half kilometer deep off the coast of Florida. She found that the distribution of debris and isotopic carbon in fossil remains was consistent with large-scale seafloor shifting triggered by hydrate decomposition and methane release.

Rapid decomposition of methane hydrates may be, at least in part, responsible for long-term global climate changes according to a group headed by James Kennett, whose paper appeared in the April 7 issue of Science. Glacial ice cores reveal that significant global temperature increases occur at intervals roughly coinciding with methane outgassing from the ocean floor.

Kennett, who is with the University of California’s Geological Sciences and Marine Science Institute, led a team which measured the isotopic carbon ratios of marine fossils over the past 60,000 years in the Santa Barbara Basin. Kennett’s group found that the isotopic ratios were indicative of huge releases of methane from the breakdown of submarine hydrates. Writing in the same issue of Science, Thomas Blunier says that this is the first direct evidence for methane release linked to climate change.

Oceanographer Bilal Hag has gone one step further by speculating, in the July 23, 1999, issue of Science, that methane-hydrate breakdown may have been instrumental in bringing the last ice age to a close 18,000 years ago.

Gerald Dickens was the lead author of an article in the Jan. 30, 1997, issue of Nature that states, “Gas hydrates in oceanic sediments may in fact comprise the Earth’s largest fossil-fuel reservoir.” A U.S. Geological Survey estimate in the March 3, 1995, issue of Science puts the amount at 13 trillion tons of methane in hydrate deposits situated at depths of a few hundred feet below sea level in oceans around the world.

Dickens points out that the amount of methane hydrate stored under the Blake Ridge, an undersea structure off the southeastern continental slope, could meet the natural gas demand in the United States for the next century. But, while energy companies are interested in methane hydrates, none are making any serious effort to exploit them. The reason can be found in an article by Robert Kleinberg and Peter Brewer in the May-June issue of American Scientist.

Methane hydrates are found everywhere in the world’s oceans where sufficiently high pressures and low temperatures allow them to form. But the deposits are usually not very thick and are spread over a wide area, giving them a very low density. The Blake Ridge deposit contains six times as much methane as the total proven U.S. reserves of natural gas but, spread over an area the size of Vermont, has a gas density of less than 2 percent of the sediment volume. This would be considered a “dry hole” in conventional natural-gas drilling.

When low yields are coupled with other problems such as crystal formation clogging drill pipes, submarine landslides and the cost of building rigs well offshore, Kleinberg and Brewer see methane hydrates as a vast resource whose exploitation lies well in the future.

Clair Wood taught physics and chemistry for more than a decade at Eastern Maine Technical College in Bangor.