Plumes of Methane

Katey Walter Anthony had been told to hunt for methane, and she could not find it.

As a young researcher at the University of Alaska, Fairbanks, she wanted to figure out how much of that gas was escaping from lakes in areas of permafrost thaw. She was doing field work in Siberia in 2000, scattering bubble traps around various lakes in the summer, but she got almost nothing.

Then, that October, the lakes froze over. Plumes of methane that had been hard to spot on a choppy lake surface in summer suddenly became more visible.

“I went out on the ice, this black ice, and it looked like the starry night sky,” Dr. Walter Anthony said. “You could see these bubble clusters everywhere. I realized — ‘aha!’ — this is where all the methane is.”

When organic material comes out of the deep freeze, it is consumed by bacteria. If the material is well-aerated, bacteria that breathe oxygen will perform the breakdown, and the carbon will enter the air as carbon dioxide, the primary greenhouse gas. But in areas where oxygen is limited, like the bottom of a lake or wetland, a group of bacteria called methanogens will break down the organic material, and the carbon will emerge as methane.

Scientists are worried about both gases. They believe that most of the carbon will emerge as carbon dioxide, with only a few percent of it being converted to methane. But because methane is such a potent greenhouse gas, the 41 experts in the recent survey predicted that it would trap about as much heat as the carbon dioxide would.

Dr. Walter Anthony’s seminal discovery was that methane rose from lake bottoms not as diffuse leaks, as many scientists had long assumed, but in a handful of scattered, vigorous plumes, some of them capable of putting out many quarts of gas per day. In certain lakes they accounted for most of the emerging methane, but previous research had not taken them into consideration. That meant big upward revisions were probably needed in estimates of the amount of methane lakes might emit as permafrost thawed.