Popping the Cap on Arctic Methane Methane held underground by caps of Arctic ice is bubbling out as a warming climate causes those caps to melt, researchers report in the journal Nature Geoscience. The paper offers some of the strongest field evidence yet that a melt-back of land ice can release methane. Removing an ice cap seems to work a bit like popping the cap on a bottle of soda, allowing pent-up gas to escape. In an interview, the paper's lead author, Katey M. Walter Anthony of the University of Alaska at Fairbanks, said that this mechanism has probably been at work since the end of the last ice age, some 10,000 years ago. "We're not necessarily saying this is a new source, so much as it's newly discovered," Dr. Walter Anthony said. And at the moment, it's not a huge source. The discovery raises concerns nonetheless. The study implies that as human-induced greenhouse gas emissions warm the planet in the coming century, the retreat of land ice throughout the Arctic will send extra methane into the atmosphere. Methane is a potent greenhouse gas itself, so such additional emissions, if large enough, could function as a feedback that would accentuate the warming. The new mechanism may sound similar to one that I described last year in an article focusing on other work by Dr. Walter Anthony on the frozen lakes of central Alaska. But the two methane sources are not the same. As that article explained, old organic material is locked up across much of the Arctic in frozen ground called permafrost, much of which dates back to the last ice age. As these shallow deposits thaw in today's warmer climate, bacteria are converting the carbon into methane and carbon dioxide, both of which are escaping into the atmosphere. The new paper describes a different type of deposit known as a geologic reservoir, in which methane gas has been trapped underground for a long time, thousands or even millions of years. Atop those deposits, land ice - in the form of permafrost, glaciers or ice caps, which are collectively known as the earth's cryosphere - has helped to keep the methane sealed underground. But now that the ice is melting, the gas can escape. Dr. Walter Anthony and her husband, a researcher named Peter Anthony, found the leaks by flying over Alaska and hiking across Greenland, looking for spots where methane from deep in the earth was bubbling vigorously enough to create holes in the ice cover of frozen lakes. They believe they have identified 150,000 seeps in Alaska alone, and they approached a fraction of them from the ground to take gas samples. The Alaskan seeps were often near the margins of retreating glaciers or thawing permafrost. In Greenland, the seeps tended to be concentrated around the margins of ice caps that have been retreating over the past 150 years, since the end of the Little Ice Age. The big question raised by the paper is exactly how big this flux of geological methane will become in a warming climate. "As the cryosphere degrades further, it could be a really big source," Dr. Walter Anthony said. Still, new findings about Arctic methane must be interpreted with caution. Researchers in recent years have repeatedly found additional sources of methane in the Arctic, and additional ways for it to escape from underground or from the sea. Writers of news articles and blog posts have often leaped to the conclusion that these fluxes are new, instead of just newly discovered, with some write-ups carrying headlines like "Arctic Armageddon." Experts say the published science on this issue does not merit such panic, at least not yet. It is true that the level of methane in the atmosphere has begun to rise in recent years, for reasons science cannot fully explain. And researchers are definitely concerned about that increase. But data from monitoring stations in the two hemispheres suggests that the increase is not coming from the Arctic. Some of it could actually be coming from increased human production of natural gas with the drilling method known as hydraulic fracturing (natural gas is mostly methane). Edward J. Dlugokencky, who monitors global methane emissions for the National Oceanic and Atmospheric Administration, said in an e-mail that the available information "does not exclude the possibility of future increasing Arctic emissions resulting from Arctic warming, but it is strong evidence that it is not happening yet." Many experts do believe, however, that the situation is urgent in a scientific sense. They say we need a much better handle on where methane is coming from today and where it could come from in the future, so as not to be caught off guard by potentially nasty surprises.