Last week I made a post about a new paper on methane seeping from the Arctic seafloor. Since then, there have been several new posts on other sites about the work, putting it into a broader perspective and also taking somewhat contradictory views of the implications of the finding. The fear is that rapid methane release is considered one plausible mechanism that could lead to abrupt climate change via various positive feedbacks in the climate system. As Nick Sundt points out (here)
A report released by the U.S. Global Change Research Program, Abrupt Climate Change, said in December 2008 (during the Bush Administration) that warming in the Arctic could cause sea levels to rise substantially beyond scientists’ previous predictions and could result in massive releases of methane. The report said that the “rapid release to the atmosphere of methane trapped in permafrost and on continental margins” was among “four types of abrupt change in the paleoclimatic record that stand out as being so rapid and large in their impact that if they were to recur, they would pose clear risks to society in terms of our ability to adapt.”
Also see lead author, Natalia Shakhova, explain the work in this video:
First, Skeptical Science has a brief but clear explanation of the study (here).
Second, Joe Romm at Climate Progress has a long and very nice post putting the study into the broader context of methane-AGW research and also nicely summarizing the related issue of terrestrial Arctic permafrost thawing.
Scientists learned last year that the permafrost permamelt contains a staggering “1.5 trillion tons of frozen carbon, about twice as much carbon as contained in the atmosphere,” much of which would be released as methane. Methane is is 25 times as potent a heat-trapping gas as CO2 over a 100 year time horizon, but 72 times as potent over 20 years!
The carbon is locked in a freezer in the part of the planet warming up the fastest (see “Tundra 4: Permafrost loss linked to Arctic sea ice loss“). Half the land-based permafrost would vanish by mid-century on our current emissions path (see “Tundra, Part 2: The point of no return” and below). No climate model currently incorporates the amplifying feedback from methane released by a defrosting tundra.
Methane is like the radical wing of the carbon cycle, in today’s atmosphere a stronger greenhouse gas per molecule than CO2, and an atmospheric concentration that can change more quickly than CO2 can. There has been a lot of press coverage of a new paper in Science this week called “Extensive methane venting to the atmosphere from sediments of the East Siberian Arctic Shelf”, which comes on the heels of a handful of interrelated methane papers in the last year or so. Is now the time to get frightened?
No. CO2 is plenty to be frightened of, while methane is frosting on the cake. Imagine you are in a Toyota on the highway at 60 miles per hour approaching stopped traffic, and you find that the brake pedal is broken. This is CO2. Then you figure out that the accelerator has also jammed, so that by the time you hit the truck in front of you, you will be going 90 miles per hour instead of 60. This is methane. Is now the time to get worried? No, you should already have been worried by the broken brake pedal. Methane sells newspapers, but it’s not the big story, nor does it look to be a game changer to the big story, which is CO2.
All three posts point out correctly that lacking time series data, there is no way to know whether the this methane flux is new and/or a result of global warming:
What’s missing from these studies themselves is evidence that the Siberian shelf degassing is new, a climate feedback, rather than simply nature-as-usual, driven by the retreat of submerged permafrost left over from the last ice age. However, other recent papers speak to this question. – David Archer
“The amount of methane currently coming out of the East Siberian Arctic Shelf is comparable to the amount coming out of the entire world’s oceans,” said Shakhova, a researcher at UAF’s International Arctic Research Center. “Subsea permafrost is losing its ability to be an impermeable cap.”
Methane is a greenhouse gas more than 30 times more potent than carbon dioxide. It is released from previously frozen soils in two ways. When the organic material (which contains carbon) stored in permafrost thaws, it begins to decompose and, under anaerobic conditions, gradually releases methane. Methane can also be stored in the seabed as methane gas or methane hydrates and then released as subsea permafrost thaws. These releases can be larger and more abrupt than those that result from decomposition.
The East Siberian Arctic Shelf is a methane-rich area that encompasses more than 2 million square kilometers of seafloor in the Arctic Ocean. It is more than three times as large as the nearby Siberian wetlands, which have been considered the primary Northern Hemisphere source of atmospheric methane. Shakhova’s research results show that the East Siberian Arctic Shelf is already a significant methane source, releasing 7 teragrams of methane yearly, which is as much as is emitted from the rest of the ocean. A teragram is equal to about 1.1 million tons.
“Our concern is that the subsea permafrost has been showing signs of destabilization already,” she said. “If it further destabilizes, the methane emissions may not be teragrams, it would be significantly larger.”
The East Siberian Arctic Shelf is a relative frontier in methane studies. The shelf is shallow, 50 meters (164 feet) or less in depth, which means it has been alternately submerged or terrestrial, depending on sea levels throughout Earth’s history. During the Earth’s coldest periods, it is a frozen arctic coastal plain, and does not release methane. As the Earth warms and sea level rises, it is inundated with seawater, which is 12-15 degrees warmer than the average air temperature.
“It was thought that seawater kept the East Siberian Arctic Shelf permafrost frozen,” Shakhova said. “Nobody considered this huge area.”
The fact sheet is a nice intro to the role of methane in global warming;
What is methane?
Methane is a naturally-occurring compound that is created when organic material, such as the remains of plants and animals, rot or otherwise break down. Bacteria and other microbes play a large role in processes that produce methane. These methane-producing processes may, for example, occur in landfills as their contents age. And some animals release methane as their bodies digest their food.
Vast stores of methane are trapped in the permafrost of the Arctic–large swaths of land where the ground stays frozen. Because of climate change, some Arctic permafrost is showing signs of thawing. This thawed Arctic permafrost may release methane into the atmosphere.
Why does methane cause so much concern?
Like carbon dioxide, methane is a greenhouse gas. The presence of greenhouse gases in the atmosphere inhibits the Earth’s heat from being released into space. Therefore, increased levels of greenhouse gases in the atmosphere may cause the Earth’s temperature to increase over time.
Methane may be “stored” underground or under the seafloor as methane gas or methane hydrate; methane hydrate is a crystalline solid combining methane and water, which is stable at low temperatures and high pressure–conditions commonly found in marine sediments. When methane stores are released relatively quickly into the atmosphere, levels of atmospheric methane may rapidly spike.
As a greenhouse gas, methane is 30 times more potent (gram for gram) than carbon dioxide. This means that adding relatively modest amounts of methane to the atmosphere may yield relatively large impacts on climate.
How much methane does it take to increase warming?
There’s no clear answer to that question. However, the Earth’s geologic record indicates that atmospheric concentrations of methane have varied from about 0.3 to 0.4 parts per million during cold periods to about 0.6 to 0.7 parts per million during warm periods.