Methane—a potent greenhouse gas that could be released in vast quantities as climate change melts Arctic permafrost—has received quite a bit of media attention in the last month. But the coverage has caused a bit of confusion about where the methane is coming from—land or sea—and which source has scientists most worried.

The first round of stories, in early December, followed the publication in the journal Nature of an analysis by forty-one scientists associated with the Permafrost Carbon Network, which found that the amount of organic carbon stored in the perennially frozen ground is 1.7-5.2 times larger than previous estimates. If released, they said, the resultant carbon dioxide and methane could play a much larger role in climate change than deforestation:

“We calculate that permafrost thaw will release the same order of magnitude of carbon as deforestation if current rates of deforestation continue,” the group wrote. “But because these emissions include significant quantities of methane, the overall effect on climate could be 2.5 times larger.”

Methane has about twenty-five times more global-warming potential than carbon dioxide over a 100-year period, and although the scientists acknowledged that it “remains highly uncertain” how much the greenhouse gases emanating from the Arctic will actually accelerate climate change, they stressed that thawing permafrost is “cause for serious concern.” Journalists such as the Associated Press’s Seth Borenstein and Time’s Bryan Walsh did a good job conveying that message, but the Knight Science Journalism Tracker’s Charlie Petit pointed out that they stumbled over one important detail.

Both reporters referred to methane and carbon dioxide being “trapped” in Arctic permafrost, but that’s not quite accurate (Borenstein explained this in the bottom half of his piece; Walsh didn’t). What’s trapped in the permafrost—on land, at least—is organic carbon in the form of ancient, frozen plant and animal matter. As the permafrost thaws, microbes decompose the plant and animal matter and produce methane and/or carbon dioxide depending on local conditions, such as the amount of oxygen present.

This seemingly nitpicking detail is important, because in areas along the Arctic seafloor, methane is trapped in the permafrost in the form of methane hydrates (also referred to as methane clathrates)—basically, methane-laced ice that forms only under high pressures and low temperatures. The second pulse of news stories about Arctic-methane this month focused on this type of deposit, which is found in relatively shallow waters along the coasts of Siberia, Canada, and Alaska.

It resulted from a scoop that Steve Connor—science editor at The Independent, a British paper—picked up while attending the American Geophysical Union’s annual meeting in December to receive an award for outstanding news reporting. The news was that the head of a Russian research team who had been studying the seabed along Russia’s northern coast had spotted “dramatic and unprecedented plumes of methane … bubbling to the surface.”

The team had published a study in 2010 describing significant “methane venting” in the area—which results when permafrost along the seafloor thaws due to the global-warming abetted retreat of insulating sea ice along the surface—but new data the group collected over the summer suggested it had underestimated the amount being vented. This methane also has the potential to accelerate climate change, but critics quickly started poking holes in Connor’s article.

The Knight Science Journalism Tracker’s Petit, who was also at the geophysical union’s meeting to receive an award (for sustained achievement in science journalism), wrote a post explaining how Connor broke away from the press pack at the meeting, and complimenting him for so doing. But “speaking of bubbling methane,” Petit observed, “I am bubbling with methane questions that this story raises.”

First and foremost, Petit wanted to know more about the source of gas. “One or two sentences on what this methane is and whether it is distinct from the kind feared from thawing, terrestrial permafrost would have answered the question,” he wrote.

Indeed, the distinction is important because the level of worry among scientists differs depending on the source—by land or by sea—of the permafrost emissions. Following Connor’s article, Andrew Revkin, who writes the New York Times Dot Earth blog, argued that:

If you read the Independent of Britain, you’d certainly be thinking the worst. The newspaper has led the charge in fomenting worry over the gas emissions, with portentous, and remarkably similar, stories in 2008 and this week.

If you read geophysical journals and survey scientists tracking past and future methane emissions, you get an entirely different picture.

Revkin cited a recent paper in the Journal of Geophysical Research, which described a worrisome feedback loop wherein climate change warms Arctic waters and reduces ice extent, thereby lengthening the summer open-water season and facilitating even more solar heating of the water column. However, the research also found that subsea permafrost and methane hydrates along the northern coast of Siberia, much of which lie deep beneath the seafloor, are relatively stable and that the observed thawing has been underway for thousands of years.

As Revkin put it in a 2010 post about oceanic Arctic methane, it’s uncertain whether these emissions are new or just newly observed. It’s also uncertain whether the thawing permafrost portends a “tipping point” beyond which there will be a rapid, inexorable melt or a more gradual, mitigable melt.

This was point addressed by Revkin’s New York Times colleague Justin Gillis in a long and wonderfully nuanced front-page article that brought the focus back to terrestrial permafrost deposits. According to his report:

In the minds of most experts, the chief worry is not that the carbon in the permafrost will break down quickly — typical estimates say that will take more than a century, perhaps several — but that once the decomposition starts, it will be impossible to stop.

Nonetheless, Gillis stressed that with an uptick in Arctic previously rare Artic wildfires, scientists fear “extensive burning could lead to a more rapid thaw of permafrost” on land. A 2008 paper in Geophysical Research Letters suggested sea-ice loss could also speed terrestrial melting. Scientists don’t seem to exhibit the same level of worry about subsea permafrost (which is not to say that they are unconcerned).

A couple days after his front-pager, Gillis followed up with a blog post explaining the discrepancy and why he chose to focus on terrestrial permafrost:

In my article over the weekend about the climate risks from buried Arctic carbon, I omitted any discussion of one issue that sometimes appears in the news: methane deposits under relatively shallow seawater near the coasts of Siberia, Canada and Alaska. It was a purposeful omission because my piece focused on carbon buried on land, which presents a climate risk if it eventually emerges as methane or carbon dioxide.

However, given the alarming headlines about methane in the ocean, as seen here and here for example, I did some additional reporting. What I learned about ocean methane was reasonably reassuring, with the caveat that scientists would like to know a great deal more about these deposits before declaring for certain that the hazard is minimal.

… Nobody regards the case as closed, and more research is necessary, but most of the methane deposits lining the margins of continents would seem to be fairly low on the list of scientific concerns about global warming.

Gillis’s post disparaged the notion, popularized by the news media, that there is a methane “time bomb” waiting to go off in the ocean. Even on land, there is little support for this idea, Revkin pointed out in yet another recent post on the subject.

“It’s not a time bomb; it’s an important additional cumulative emissions source,” Edward Shurr—one of the forty-one scientists who wrote the Nature analysis describing the larger-than-realized store of Arctic carbon—told him.

It’s important to keep these details—including the difference between terrestrial and oceanic permafrost emission—in mind, because they have direct bearing on the “list of scientific concerns about global warming” that Gillis mentioned, and on how we might prioritize various measures to address climate change.

For instance, the forty-one scientists writing in Nature emphasized that, “despite the massive amount of carbon in permafrost soils, emissions from these soils are unlikely to overshadow those from the burning of fossil fuels, which will continue to be the main source of climate forcing.”

Comments like that should make people think twice about proposals to geo-engineer a cooling effect in the Arctic, such as one recently presented at the American Geophysical Union and described in an article at New Scientist.

How problematic methane (and carbon dioxide) from Arctic permafrost will be remains a mystery. A useful 2010 overview in the journal Science, titled “How Stable Is the Methane Cycle?”, emphasized the importance of resolving lingering uncertainties. Thankfully, researchers are on the case, according to a December 19 article in Nature, which highlighted the fact “permafrost science is heating up in the United States.”

As scientists continue to work out the complex physical and chemical processes playing out in the Arctic, it will be incumbent upon journalists to convey important nuances about both terrestrial and oceanic methane, and how both fit into the larger picture of Earth’s changing climate.

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Curtis Brainard is the editor of The Observatory, CJR's online critique of science and environment reporting. Follow him on Twitter @cbrainard.