For some time, scientists fearing the mass release of greenhouse gases from the carbon-rich, frozen soils of the Arctic have had at least one morsel of good news in their forecasts: They predicted most of the gas released would be carbon dioxide, which, though a greenhouse gas, drives warming more slowly than some other gases. Scientists obviously weren’t excited about more carbon dioxide emissions, but it was better than the alternative: methane, a shorter-lived but far harder-hitting gas that could cause faster bursts of warming.
Now even that silver lining is in doubt.
Research released Monday suggests that methane releases could be considerably more prevalent as Arctic permafrost thaws. The research finds that in waterlogged wetland soils, where oxygen is not prevalent, tiny microorganisms will produce a considerable volume of methane, a gas that doesn’t last in the air much more than a decade but has a warming effect many times that of carbon dioxide over a period of 100 years.
“What we can definitely say is that the importance of methane was underestimated until now in the carbon studies,” said Christian Knobloch, a researcher at Universität Hamburg in Germany and the lead author of the study, published in Nature Climate Change.
The divergent finding came after Knoblauch and his colleagues conducted a lengthy experiment, more than seven years long, monitoring patches of submerged and artificially warmed soil from Siberia in the laboratory, and gradually seeing sensitive methane-producing microorganisms become more prevalent over time.
Knoblauch contends that other studies have not examined waterlogged Arctic soils for as long, and he notes that in some cases it took three years or more for the methane-generating microorganisms to really get cranking.
“What we saw is that it takes a very long time until methane starts being produced, and the study that we did is really the first one which is so long,” Knoblauch said.
The research was conducted along with colleagues from several institutions in Germany, Sweden and Russia.
So much methane was produced in the experiment, the researchers calculated that the impact of greenhouse gas emissions from wet soils, or wetlands, will be higher than from drier soils, where carbon dioxide should indeed be the top gas released. This finding, if further confirmed, could reorient calculations of the overall potential of permafrost to worsen global warming over the coming century.
For instance, one major study of the permafrost warming potential, published in 2015 in the journal Nature, played down the potential for methane release in wet soils, saying drier soils would be the bigger problem.
“In spite of the more potent greenhouse gas CH4, a unit of newly thawed permafrost carbon could have a greater impact on climate over a century if it thaws and decomposes within a drier, aerobic soil as compared to an equivalent amount of carbon within a waterlogged soil or sediment,” that research found. The new study would appear to contradict this.
But Knoblauch cautions that more research would have to be done to go from these results to a forecast for just how much methane could waft from permafrost in the coming decades. It will be important to know, for instance, how much thawed permafrost will be stuck in watery conditions vs. dry ones.
One Arctic permafrost expert not involved in the research, Merritt Turetsky of the University of Guelph, praised the new study, noting that the researchers had spent a long time trying to uncover the behavior of tiny methane-producing organisms in watery soil. The research, she said, could help bridge the gap between field studies of waterlogged permafrost that have detected methane emissions and laboratory studies that have seemed to play down the importance of the gas.
“What’s remarkable about this study is the length of time they spent tracking the communities, and I think that offers a potential reason for why field and lab studies have disagreed with each other,” Turetsky said.
She said the total amount of permafrost carbon that could be vulnerable because of global warming during this century — perhaps 10 percent of it, which would be more than enough to undermine global climate goals — probably won’t change in light of the new research. But the fraction of that carbon that is emitted as methane, as opposed to carbon dioxide, will be crucial, she said, and remains to be determined.
“We absolutely have to partition that total permafrost carbon release into those two forms, because it really matters,” Turetsky said. “So I think that has got to be where the community goes next.”
But Róisín Commane, a research associate at Harvard who studies the Arctic atmosphere and also was not involved in this research, was more skeptical about relying on this study to assume a worse verdict about methane.
The study was “very nicely done,” she said, but the tendency of wet soils to produce methane could be counteracted by several factors. The soils could also become host to organisms that devour that methane — and turn it into carbon dioxide. And, as the Arctic continues to warm, soils might not retain as much water, as the subsurface ice that held it in place gradually gives way, she noted.
“How much of it makes it into the atmosphere is the big thing,” Commane said. “Ecosystems will probably produce more methane as they stay wet. The big question we have is, how much of that makes it into the atmosphere, and I don’t think they get to that question here.”