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In the early 1980s, as a newly minted Ph.D. teaching at the Oregon Graduate Institute, Aslam Khalil, now PSU professor of physics, almost by accident began looking at measurements of methane gas in the atmosphere. Noticing that methane levels were on the rise, Khalil innocently published his findings.

The scientific community took umbrage. Methane, said members, was a stable atmospheric gas—just read the textbooks on it.

Khalil and others refuted the conventional wisdom by examining data from ice core samples. They found that methane has more than doubled since pre-industrial times—from 700 to 800 parts per billion in pre-industrial times to 1,700 parts per billion currently.

But it was when Khalil and others discovered the mechanics of how methane is produced that things got interesting. The three primary sources are:

• Natural gas and crude oil—18 percent
• Burping livestock and their manure—19 percent
• Bacteria-infested rice paddies and wetlands—37 percent

It was that last one, in particular rice, that caught Khalil’s scientific interest.

Rice is grown in a sort of layer cake of water, mud and impermeable clay. In that environment, are specialized bacteria that produce methane. As they give off the methane, most of the gas is eaten by a second bacteria that either lives on or in the rice roots—no one’s quite sure. The organisms eat about 75 percent of the methane; the rest passes out through the tops of the rice plant—almost like a chimney emitting smoke.

“The plant supplies the carbon, host, and conduit,” says Khalil. “Any change in this complex mechanism results in a change in methane emissions.”

Now, Khalil and his colleagues at Oregon Health & Science University (OHSU) are finding that the buildup of methane in the atmosphere is slowing and has been for a quarter of a century. A key reason may be from changes in the way China grows rice.

For the past 30 years, China’s rice-growing areas have shrunk and farmers have replaced methane generating organic fertilizers, animal and human excrements, with nitrogen-based fertilizers. Growers are also using less water, which reduces methane emissions.

“There may be methane sources that are increasing, but they are being balanced by the decrease in methane from rice fields,” says Khalil.

Methane, considered the second most detrimental greenhouse gas after carbon dioxide, traps heat 20 times more efficient than CO2. Both gases bear the greenhouse gas label because they allow sunlight to enter our atmosphere freely, but when that energy is sent back towards space as infrared radiation, they absorb the heat—a process that causes the greenhouse effect and global warming if the gases increase.

Khalil’s findings that methane build-up is slowing is supported by the U.S. Environmental Protection Agency. It recently released a 2007 Draft U.S. Greenhouse Gas Inventory Report showing that methane emissions in the United States have decreased over the past decade.

Khalil’s body of research also has garnered praise from science’s highest realms. Paul Crutzen, who shared the 1995 Nobel Prize in Chemistry for his work on understanding the causes of the hole in the earth’s ozone, cited Khalil and OHSU’s Reinhold Rasmussen for their ongoing research in his acceptance lecture.