Methane also is present in another form, as hydrates — ice-like formations deep underground and under the seabed in which methane molecules are trapped within crystals of frozen water. If warmed, the methane will escape.
Dallimore, who has long researched hydrates as energy sources, believes a breakdown of such huge undersea formations may have produced conical "hills" found offshore in the Beaufort Sea bed, some of them 40 meters (more than 100 feet) high.
With underwater robots, he detected methane gas leaking from these seabed features, which resemble the strange hills ashore here that the Inuvialuit, or Eskimos, call "pingos." And because the coastal plain is subsiding and seas are rising from warming, more permafrost is being inundated, exposed to water warmer than the air.
The methane seeps that the Canadians were studying in the Mackenzie Delta, amid grassy islands, steel-gray lakes and summertime temperatures well above freezing, are saucer-like indentations just 10 meters (30 feet) or so down on the lake bed.
The ultimate source of that gas — hydrates, decomposition or older natural gas deposits — is unclear, but Dallimore's immediate goal is quantifying the known emissions and finding the unknown.
With tent-like, instrument-laden enclosures they positioned over two seeps, each several meters (yards) wide, the researchers have determined they are emitting methane at a rate of up to 0.6 cubic meters (almost 1 cubic yard) per minute.
Dallimore's team is also monitoring the seeps with underwater listening devices, to assess whether seasonal change — warming — affects the emissions rate.
Even if the lake seeps are centuries old, Bowen said, the question is, "Will they be accelerated by recent changes?"
A second question: Are more seeps developing?
To begin answering that, Dallimore is working with German and Canadian specialists in aerial surveying, teams that will fly over swaths of Arctic terrain to detect methane "hot spots" via spectrometric imagery, instruments identifying chemicals by their signatures on the light spectrum.
Research crews are hard at work elsewhere, too, to get a handle on this possible planetary threat.
"I and others are trying to take field observations and get it scaled up to global models," said Alaska researcher Schuur. From some 400 boreholes drilled deep into the tundra worldwide, "we see historic warming of permafrost. Much of it is now around 2 below zero (28 F)," Schuur said.
A Coast Guard C-130 aircraft is overflying Alaska this summer with instruments sampling the air for methane and carbon dioxide. In parts of Alaska, scientists believe the number of "thermokarst" lakes — formed when terrain collapses over thawing permafrost and fills with meltwater — may have doubled in the past three decades. Those lakes then expand, thawing more permafrost on their edges, exposing more carbon.
Off Norway's Arctic archipelago of Svalbard last September, British scientists reported finding 250 methane plumes rising from the shallow seabed. They're probably old, scientists said, but only further research can assess whether they're stable. In March, Norwegian officials did say methane levels had risen on Svalbard.
Afloat above the huge, shallow continental shelf north of Siberia, Russian researchers have detected seabed "methane chimneys" sending gas bubbling up to the surface, possibly from hydrates.