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Global warming may be unleashing new sources of heat-trapping methane from layers of oil and gas that have been buried deep beneath Arctic permafrost for millennia. As the Earth's frozen crust thaws, some of that gas appears to be finding new paths to the surface through permafrost that's starting to resemble Swiss cheese in some areas, scientists said.
In a study released today, the scientists used aerial sampling of the atmosphere to locate methane sources from permafrost along a 10,000 square-kilometer swath of the Mackenzie River Delta in northwestern Canada, an area known to have oil and gas desposits.
Deeply thawed pockets of permafrost, the research suggests, are releasing 17 percent of all the methane measured in the region, even though the emissions hotspots only make up 1 percent of the surface area, the scientists found.
In those areas, the peak concentrations of methane emissions were found to be 13 times higher than levels usually caused by bacterial decomposition—a well-known source of methane emissions from permafrost—which suggests the methane is likely also coming from geological sources, seeping up along faults and cracks in the permafrost, and from beneath lakes.
The findings suggest that global warming will "increase emissions of geologic methane that is currently still trapped under thick, continuous permafrost, as new emission pathways open due to thawing permafrost," the authors wrote in the journal Scientific Reports. Along with triggering bacterial decomposition in permafrost soils, global warming can also trigger stronger emissions of methane from fossil gas, contributing to the carbon-climate feedback loop, they concluded.
"This is another methane source that has not been included so much in the models," said the study's lead author, Katrin Kohnert, a climate scientist at the GFZ German Research Centre for Geosciences in Potsdam, Germany. "If, in other regions, the permafrost becomes discontinuous, more areas will contribute geologic methane," she said.
Similar Findings Near Permafrost Edges
The findings are based on two years of detailed aerial atmospheric sampling above the Mackenzie River Delta. It was one of the first studies to look for sources of deep methane across such a large region.
Previous site-specific studies in Alaska have looked at single sources of deep methane, including beneath lakes. A 2012 study made similar findings near the edge of permafrost areas and around melting glaciers.
Now, there is more evidence that "the loss of permafrost and glaciers opens conduits for the release of geologic methane to the atmosphere, constituting a newly identified, powerful feedback to climate warming," said the 2012 study's author, Katey Walter Anthony, a permafrost researcher at the University of Alaska Fairbanks.
"Together, these studies suggest that the geologic methane sources will likely increase in the future as permafrost warms and becomes more permeable," she said.
"I think another critical thing to point out is that you do not have to completely thaw thick permafrost to increase these geologic methane emissions," she said. "It is enough to warm permafrost and accelerate its thaw. Permafrost that starts to look like Swiss cheese would be the type that could allow substantially more geologic methane to escape in the future."
Róisín Commane, a Harvard University climate researcher, who was not involved with the study but is familiar with Kohnert's work, said, "The fluxes they saw are much larger than any biogenic flux ... so I think a different source, such as a geologic source of methane, is a reasonable interpretation."
Commane said the study makes a reasonable assumption that the high emissions hotspots are from geologic sources, but that without more site-specific data, like isotope readings, it's not possible to extrapolate the findings across the Arctic, or to know for sure if the source is from subsurface oil and gas deposits.
"There doesn't seem to be any evidence of these geogenic sources at other locations in the Arctic, but it's something that should be considered in other studies," she said. There may be regions with pockets of underground oil and gas similar to the Mackenzie River Delta that haven't yet been mapped.
Speed of Methane Release Remains a Question
The Arctic is on pace to release a lot more greenhouse gases in the decades ahead. In Alaska alone, the U.S. Geological Survey recently estimated that 16-24 percent of the state's vast permafrost area would melt by 2100.
In February, another research team documented rapidly degrading permafrost across a 52,000-square-mile swath of the northwest Canadian Arctic.
What's not clear yet is whether the rapid climate warming in the Arctic will lead to a massive surge in releases of methane, a greenhouse gas that is about 28 times more powerful at trapping heat as carbon dioxide but does not persist as long in the atmosphere. Most recent studies suggest a more gradual increase in releases, but the new research adds a missing piece of the puzzle, according Ted Schuur, a permafrost researcher at Northern Arizona University.
Since the study only covered two years, it doesn't show long-term trends, but it makes a strong argument that there is significant methane escaping from trapped layers of oil and gas, Schuur said.
"As for current and future climate impact, what matters is the flux to the atmosphere and if it is changing ... if there is methane currently trapped by permafrost, we could imagine this source might increase as new conduits in permafrost appear," he said.