Termites not to blame for methane.

Termites not to blame for methane

As concern builds over the threat of global warming, scientists are trying to understand why atmospheric levels of methane, a greenhouse gas, have more than doubled in the last two centuries. Researchers in the early 1980s suggested termites may deserve partial blame for the increase, but a comprehensive study downplays their role.

"Although the uncertainties are still very large, the weight of the scientific evidence is shifting toward the conclusion that termites are not an important global sources of methane," report M. Aslam K. Khalil and R.A. Rasmussen at the Oregon Graduate Center in Beaverton along wth Australian colleagues. They describe their work in the March 20 JOURNAL OF GEOPHYSICAL RESEARCH.

The researchers measured gases emitted by six termite species in Australia and reviewed the published data concerning how much food termites consume. They estimate termites worldwide emit about 12 X [10.sup.12] grams per year of methane, which amounts to about 2 percent of the methane released by all global sources each year. This number agrees with results from lab measurements and a field study in Africa.

In 1982, researchers from the National Center for Atmospheric Research in Boulder, Colo., sparked the debate over termites when they reported estiamtes based on laboratory work that termites emit 150 X [10.sup.12] grams each year, which would constitute about 30 percent of the world's annual methane emissions. They also suggested that human activities such as deforestation have boosted termite populations, which could explain part of the rise in methane concentrations.

Khalil says the earlier study overestimated the amount of food consumed by termites each year and did not take into account methane absorption by the ground near their mounds, a fact discovered only during field experiments. According to Khalil, the methane buildup in the atmosphere stems not from a population explosion in termites but from increasing numbers of rice fields, cattle and sheep.