This tends to freak us out, and not surprisingly. After all, one leading idea about the source of the mysterious craters is that these might represent explosions of methane gas into the atmosphere — liberated by melting Arctic permafrost, which is, of course, destabilizing because of global warming.
“What I think is happening here is, the permafrost has been acting as a cap or seal on the ground, through which gas can’t permeate,” says Paul Overduin, a senior scientist at the Alfred Wegener Institute in Germany who studies permafrost, of the craters. “And it reaches a particular temperature where there’s not enough ice in it to act that way anymore. And then gas can rush out.”
Here’s why this is scary: If large amounts of methane vent from the Arctic into the atmosphere, that could lead to a positive climate change feedback — still more warming, still more methane release, and so on and so on and so on. That’s because methane is not only a greenhouse gas, but a potent one at that — pound for pound, it causes much more global warming than carbon dioxide does (though, fortunately, it does not last nearly as long in the atmosphere).
However, it all really depends on how much methane is venting — and, so far, it’s not clear that it’s very much.
Reasons for not worrying
First of all, there’s the scale of the craters. When news of them first emerged, the climate researcher David Archer of the University of Chicago took a look at their size — one of the craters, he wrote, was “about 80 meters in diameter and 60-100 meters deep” — and did some quick calculations. And he concluded that “it would take about 20,000,000 such eruptions within a few years to generate the standard Arctic Methane Apocalypse that people have been talking about.”
There’s also the fact that if the Arctic was really becoming a methane bomb, we would presumably be able to measure that. The National Oceanic and Atmospheric Administration takes atmospheric measurements of greenhouse gases, including methane, explains the agency’s Ed Dlugokencky, who monitors these global greenhouse gas emissions for the agency. When it comes to measuring methane release in the Arctic and whether it is increasing, NOAA does so through two methods: combining actual measurements of methane in the air with a “model of atmospheric chemistry and transport” and examining whether there are “spatial patterns in measurements over time,” Dlugokencky says.
“So far, neither of these approaches suggests a detectable increase in emissions from the Arctic,” he says.
Granted, methane in the atmosphere is increasing, and has been since 2007 — it’s just that NOAA doesn’t have evidence of an Arctic uptick in particular. And it’s important to emphasize that NOAA’s data are pretty up to date. The measurements are taken on a roughly weekly basis — and “for most high northern latitude sites, we have data to near the end of 2014,” says Dlugokencky.
Still, the craters could still be seen as an ominous harbinger. “I see this as a new phenomenon, pointing to the warming of permafrost. So it’s not just warming up, it’s also erupting,” Overduin says. But he notes that there’s no way to know right now how significant the eruptions are, in a climatic sense.
So what about methane beneath the ocean surface?
The Siberian craters story also needs to be understood alongside another Arctic methane story that has been popping in and out of the news and people’s consciousness for several years. It’s kind of the oceanic version of the craters: The idea that frozen permafrost beneath the sea surface just offshore in Arctic regions also may explosively release methane that is currently stored in “gas hydrates,” or icy deposits beneath the seafloor.
This prospect, too, has been depicted as very alarming.
But a number of scientists have said that, with respect to methane emissions from sub-sea permafrost, we should chill out. Like all Arctic matters — where we have a vast area that’s changing rapidly but few researchers able to even reach most parts of it — this is another realm that’s rife with scientific uncertainty. But it remains questionable at this point that any Arctic methane catastrophe is underway.
Globally, it is estimated that a very large amount of methane — though estimates vary widely — is trapped beneath the seafloor in the form of “methane hydrates,” frozen combinations of ice and gas. Warming ocean waters could melt these hydrates, but most of them are thought to be in very deep waters, where warmth probably wouldn’t reach, at least not anytime soon. Moreover, if methane gets released from the seafloor in deep ocean water, much of the gas would probably dissolve in the water column without necessarily reaching the surface.
So the key issue here would seem to be how much methane hydrate exists in shallow waters of continental shelves, which could be destabilized in close proximity to the atmosphere. And one recent study found that that’s probably about 1 percent of all global methane that’s stored in gas hydrates. “There’s probably less permafrost associated gas hydrate than some of the assumptions that are made,” explains its author Carolyn Ruppel, a gas hydrate researcher with the U.S. Geological Survey.
Granted, at least one team of researchers would appear to disagree. Natalia Shakhova of the University of Alaska Fairbanks and her colleagues published a study in Nature Geoscience last year suggesting that “significant quantities of methane are escaping the East Siberian Shelf as a result of the degradation of submarine permafrost over thousands of years.” Ruppel doesn’t question the research but says that “we go to other places in high latitudes and we try to measure methane fluxes, and we don’t get numbers that are anywhere near as high.”
The National Academy of Sciences, when it looked at risks of “abrupt” climate change in 2013, similarly rated the risk of an Arctic methane bomb quite low. On the subject of sub-sea permafrost releasing methane, the report said this was unlikely to lead to abrupt climate change in this century. As for land-based permafrost, the report had a similar message. “Arctic carbon stores are poised to play a significant amplifying role in the century-scale buildup of carbon dioxide and methane in the atmosphere, but are unlikely to do so abruptly, i.e., on a timescale of one or a few decades,” it found.
So, at a minimum, we would have to say that a risk from sub-sea Arctic methane is, at this point, contested.
The Arctic is changing very rapidly indeed, and there is every reason to expect that as permafrost melts, we will see more carbon dioxide and more methane vent into the atmosphere. And that is not a good thing. However, that doesn’t mean that a methane catastrophe is coming anytime soon. We should be cautious and worried about what’s happening to the Arctic — but not, yet, alarmist.
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