Vast reservoirs of methane – a greenhouse gas 30 times more potent than carbon dioxide – lie beneath the permafrost, and as global temperatures rise and the permafrost thaws, it could leak out and speed up the pace of climate change in an ever-faster vicious circle.
A team of researchers from Germany spent two years measuring the release of methane from the Mackenzie River Delta in northern Canada. They were trying to figure out how much of the gas was the normal “biogenic” emissions produced each summer by decomposing organic matter in Arctic wetlands, and how much is coming from ancient underground “geologic” sources leaking through gaps in the permafrost year-round.
The scientists used aircraft to collect and analyze air samples in a survey of 10,000 square kilometres (4,000 square miles) of the delta and found that the area produces about 38,000 tons of methane each year. Geologic methane was detected in about 1 percent of the area studied, but it made up 17 percent of the total emissions.
“The geologic methane emissions per square meter are much stronger than those biogenic emissions,” said Katrin Kohnert, a climate scientist at the German Research Center for Geosciences in Potsdam and an author of the study, published last week in the journal Scientific Reports.
Geologic methane can find its way to the surface in the delta because the permafrost there, especially in the northern part, is much thinner than in neighbouring areas – just 100 metres (330 feet) thick compared with up to 500 metres (1,640 feet) on nearby Richards Island. The delta permafrost also has many gaps – permanently thawed areas called taliks that often form under water bodies. This gives the geologic methane, produced millions of years ago but locked beneath the ground, a path to the surface.
And there is a lot of it there. In 2009, one study estimated there could be anywhere from 170 billion cubic meters to 2.8 trillion cubic meters (6 trillion to 100 trillion cubic feet) of undiscovered gas in the northern Mackenzie Delta. Kohnert and her colleagues did not study the emissions for long enough to determine if methane levels were getting stronger, but they say that as more permafrost thaws, it will form new lakes and taliks and open up more cracks and gaps for the gas to follow.
Ko van Huissteden, a climate scientist at the Free University Amsterdam, says it is plausible that geologic methane emissions will become stronger as the permafrost degrades. Similar results have been seen in Alaska and on Siberia’s Yamal peninsula, where hundreds of methane-spewing craters formed by gas explosions dot the landscape. But he says the evidence is weak that the higher than average methane emissions in the Mackenzie Delta measured by Kohnert and her colleagues are the result of geologic leaks.
The researchers inferred how much geologic methane had been released based on past research that suggests biogenic methane doesn’t exceed certain levels, reasoning that anything exceeding those levels must have been driven by methane released from underground. But a more rigorous approach, says Van Huissteden, would test the chemical makeup of the methane – gas from ancient geologic sources and recent biological ones will have different ratios of isotopes of carbon and hydrogen. And he questions the assumption that emissions from geologic sources should necessarily be higher than biogenic ones. Van Huissteden’s own research in Siberia found emissions from biological sources that were almost four times higher than the limit imposed by Kohnert in her paper.
“The idea that these high emissions from the Mackenzie Delta are geologic emissions remain an assumption, although a plausible one, which needs better evidence,” said Van Huissteden.
The uncertainty highlights the biggest problem with trying to understand what impact climate change will have on Arctic permafrost, and what effect the thawing permafrost will have on climate change – scientists still don’t have enough data to make valid predictions, he says.
Some climate models take biological methane emissions into account, but the estimates diverge so much that it is very difficult to get meaningful results. And Van Huissteden doesn’t know of any models that even attempt to incorporate geologic emissions.
“We can guess that methane will be released, and make estimates, but those estimates need to be based on ground-based research,” he said. “There’s very little of that in the Arctic, in the last 10 years we have – quite literally – only just started to scratch the surface.”