Thoughts in a Haystack

The question has cast a spotlight on a group of scientists more used to leading quiet lives of research, often peering through fistulas positioned on the sides of cows to give direct access to their guts. The scientists, rumen microbiologists — "We're quite a few; you'd be amazed," Mr. Klieve said — study the stomachs of ruminants like cows, sheep and deer.

Ruminants release methane because of the peculiar way they digest their food. Inside a cow's foregut, which can contain more than 200 pounds of grass at any given time, fermentation of the food leads to the release of hydrogen, a byproduct that would slow down the fermentation. Microbes known as methanogens help the ruminants get rid of the excess hydrogen by producing methane gases that the animals release into the atmosphere.

In other animals known as hindgut fermenters, including humans — in which food is fermented after going through their stomachs — methane is sometimes released through flatulence, a fact that, Mr. Klieve said, has led to misunderstanding about his work

"We've had to put up with that all the time," Mr. Klieve said. "It comes from the front end! In the cow, it comes from the front end. But if you're a hindgut fermenter, it goes the other way."