Climate scientists have long warned that global warming could unlock vast stores of the greenhouse gas methane that are frozen into the Arctic permafrost, setting off potentially significant increases in global warming.
Now researchers at the University of Alaska, Fairbanks, and elsewhere say this change is under way in a little-studied area under the sea, the East Siberian Arctic Shelf, west of the Bering Strait.
Natalia Shakhova, a scientist at the university and a leader of the study, said it was too soon to say whether the findings suggest that a dangerous release of methane looms. In a telephone news conference, she said researchers were only beginning to track the movement of this methane into the atmosphere as the undersea permafrost that traps it degrades.
But climate experts familiar with the new research reported in Friday’s issue of the journal Science that even though it does not suggest imminent climate catastrophe, it is important because of methane’s role as a greenhouse gas. Although carbon dioxide is far more abundant and persistent in the atmosphere, ton for ton atmospheric methane traps at least 25 times as much heat.Continue reading the main story
Until recently, undersea permafrost has been little studied, but work so far shows it is already sending surprising amounts of methane into the atmosphere, Dr. Shakhova and other researchers are finding.
Last year, scientists from Britain and Germany reported that they had detected plumes of methane rising from the Arctic seabed in the West Spitsbergen area, north of Scandinavia. At the time, they said they had begun their work hoping to gain data to predict future emissions and had not expected to find evidence that the process was under way.
It is “indispensable” to keep track of methane in the region, Martin Heimann of the Max Planck Institute in Germany said in a commentary accompanying the Science report. So far, Dr. Heimann wrote, methane contributions from Arctic permafrost have been “negligible.” He added: “But will this persist into the future under sustained warming trends? We do not know.”
In an e-mail message, Euan G. Nisbet of the University of London, an expert on atmospheric methane, said the situation “needs to be watched carefully.”
Atmospheric concentrations of methane have more than doubled since pre-industrial times, Dr. Heimann wrote. Most of it comes from human activities including energy production, cattle raising and the cultivation of rice. But about 40 percent is natural, including the decomposition of organic materials in wetlands and frozen wetlands like permafrost.
Dr. Shakhova said that permafrost in the East Siberian Arctic Shelf, peat land that flooded as sea levels rose after the last ice age, is degrading in part because runoff from rivers that feed the Arctic Ocean is warmer than in the past.
She estimated that annual methane emissions from the East Siberian Arctic Shelf total about seven teragrams. (A teragram is 1.1 million tons.) By some estimates, global methane emissions total about 500 teragrams a year.
Dr. Shakhova said that undersea methane ordinarily undergoes oxidation as it rises to the surface, where it is released as carbon dioxide. But because water over the shelf is at most about 50 meters deep, she said, the gas bubbles to the surface there as methane. As a result, she said, atmospheric levels of methane over the Arctic are 1.85 parts per million, compared to a global average of 1.7 parts per million. Concentrations over the shelf are 2 parts per million or higher.
But, “I am not the person to judge” whether the Arctic findings suggest that estimates of climate change in coming decades should be rewritten, she added.
“I would not go so far as to suggest any implications,” she said. “We are at the very beginning of research.”
An article on Friday about a study that indicated that methane is leaking into the atmosphere from the East Siberian Arctic Shelf misquoted a researcher at the University of Alaska, Fairbanks, who, speaking by telephone, gave an estimate of the average atmospheric concentration of methane worldwide. The researcher, Natalia Shakhova, said it was 1.7 parts per million, not 0.6 or 0.7 parts per million.
An earlier version of this article incorrectly referred to a teragram being 1.1 billion tons. It is 1.1 million tons. The version also incorrectly said that the East Siberian Arctic Shelf is east of the Bering Strait. It is west of the Bering Strait.