A permafrost region in East Siberia has emerged as a previously unknown source of nitrous oxide, a greenhouse gas that carries nearly 300 times the warming potential of carbon dioxide over a 100-year span, a team of researchers from the University of Eastern Finland reported yesterday in the journal Nature Communications.
While annual nitrous oxides releases due to human activity have increased 30% by 1980, and alarmed scientists have been paying attention, nitrous emissions from permafrost would be a largely new twist in the effort to get greenhouse gases and the resulting climate emergency under control.
“The nitrous oxide emissions from thawing permafrost represent a poorly known, but potentially globally significant positive feedback to climate change,” the university writes in a release. “Overall, the consequences of nitrogen release from permafrost for Arctic ecosystems have been insufficiently studied and remain poorly understood.”
What’s known is that “rapid Arctic warming and associated permafrost thaw are threatening the large carbon and nitrogen reservoirs of northern permafrost soils, accumulated under cold conditions where the decomposition rate of soil organic matter (SOM) is low,” concludes the science team led by post-doctoral researcher Maija Marushchak. As the permafrost thaws, those pools are decomposing.
While “the fate of soil nitrogen liberated upon permafrost thaw is poorly studied and more complex” than carbon release, the scientists add, “there is evidence that part of liberated nitrogen may be emitted to the atmosphere as nitrogenous gases.”
Temperatures in Arctic Siberia were more than 6°C above average last year, states the Copernicus Climate Change Service, representing “the largest anomalies worldwide in 2020”. That heat wave was made 600 times more likely by climate change, Carbon Brief reported at the time, citing analysis by the World Weather Attribution network.
The researchers looked at the Yedoma permafrost, a large, until now frozen expanse that dates back to the Late Pleistocene age. They focused on the riverbanks of the East Siberian rivers Lena and Kolyma, where rapid permafrost thaw has exposed Yedoma permafrost to the surface and triggered large carbon and nitrogen releases due to microbial activity.
“The researchers found that nitrous oxide emissions from recently thawed Yedoma were initially very low but increased within less than a decade to high rates, exceeding typical emissions from permafrost-affected soils by one to two orders of magnitude (10-100 times),” the release states. The increase occurred when the Yedoma sediments dried out after they thawed, and also had to do with a shifting balance between microbes that consume nitrous oxide precursors like nitrate and nitric oxide, and those that produce it.
Marushchak told The Energy Mix there are too many unknowns to estimate the total nitrous oxide released from Yedoma permafrost in Siberia, Alaska, and Canada’s Yukon Territory at today’s level of global warming. But with the climate community aiming for future climate stabilization at 1.5 to 2.0°C, and most projections pointing to still larger increases in global heating, “we can expect higher nitrous oxide emissions with warmer temperatures, because warming will accelerate the rate of permafrost thaw and thus mobilization of nitrogen from permafrost,” she wrote in an email.
She added that factors like soil moisture are even more important than temperature, with the highest risk coming from soils that are neither too wet nor too dry.
In the university news release, Marushchak said nitrogen released by thawing permafrost “can substantially improve the availability of nitrogen in Arctic ecosystems, which, in addition to the direct climatic feedback in the form of nitrous oxide, may have important consequences on carbon fixation by plants and eutrophication of water systems.” In her email, she said there isn’t enough information on Arctic biogeochemistry to weigh the cooling effect of increased plant growth and carbon fixation against the increased nitrous oxide emissions that might come from northern rivers and lakes.
Whichever way that balance goes, there will be only one path for humanity to try to shift the outcome.
“Unfortunately, there is no way to directly control or reduce permafrost thaw-related N2O emissions over vast, remote Arctic areas,” Marushchak wrote. “The best possibility to protect permafrost worldwide and to prevent mobilization of its carbon and nitrogen stocks is to reduce anthropogenic emissions related to fossil fuel combustion and land use,” including nitrous oxide emissions from agriculture.
University of Ottawa permafrost specialist Antoni Lewkowicz said the same processes could unfold in Canada, but the emission rates may differ and the country doesn’t have very many deposits of Yedoma permafrost.
But “we have had many surprises regarding emissions of greenhouse gases from thawing permafrost over the past decade,” he told The Mix. “This study falls into that category. Permafrost areas are vast and heterogeneous and we still have a great deal to learn about biogeochemical cycling as the climate warms.”