1 April 2020

Lower estimates of Arctic methane emissions thanks to upland soil microbes

Nature Climate Change

A new model study has revised estimates of net methane emissions from the Arctic. The model work considers not only methane emitted by wetland methane-producing microbes (methanogens), but also methane consumed by upland methane-oxidising microbes (methanotrophs), and the effects of these microbes in a warmer climate. Results published in Nature Climate Change show that, while there will likely be more methane emitted to the atmosphere — and still a concerning amount —, the net emissions from the Arctic may be much smaller than expected.

Barren ground in Peary Land in North Greenland. Despite the apparent lack of life, these soils host bacteria responsible for some of the highest rates of methane consumption from the atmosphere (photo: Bo Elberling).

Professor Zhuang and Ph.D. student Youmi Oh from the Departments of Earth, Atmospheric, and Planetary Sciences and Agronomy, who have lead the model development, said: “The emissions from wetlands will potentially be quite large, but if you consider the uplands, then the area-aggregated net emissions will be much smaller than previously thought.”

Arctic wet soils emit methane to the atmosphere when the methane production by methanogens is larger than the methane consumption by methanotrophs. The methanotrophs in those soils require high-level methane concentrations to survive and reproduce. In contrast, high-affinity methanotrophs in Arctic mineral uplands require less than 1% of the methane concentration level that allows their wetland counterparts to thrive. That means they can survive and reproduce on low atmospheric methane concentration levels and thereby pull out methane from the atmosphere.

Field observations of methane oxidation in the Arctic are limited. At the Center for Permafrost (CENPERM), Department of Geosciences and Natural Resource Management at the University of Copenhagen detailed measurements have been made to quantify seasonal trends in methane oxidation at sites across Greenland. Postdoc Ludovica D’Imperio and professor Bo Elberling from CENPERM have been responsible for the data collection and for the inclusion of field data in the current model work. Elberling said ”The work is an example of the importance of a close collaboration between modellers and field scientists. The current model results are the first step in further downscaling with more high-resolution data, which is already ongoing for Greenland. Greenland is different from the average Arctic region due to the limited amount of wetlands and vast amount of dry upland soils. In that sense, Greenland is already now considered a net sink of methane, meaning that the amount of methane taken out of the atmosphere exceeds the amount being released from the wetlands.

Oh continues: “We do believe that Arctic methane emissions will increase by the end of this century as other studies have shown, but the net increase to the atmosphere will be much smaller once upland methanotrophs are taken into consideration. The current model work assumes that wetland and upland areas will not change in the future. We know, however, that changes in temperature, precipitation and other factors will impact areal dynamics of wetland versus upland areas, thus methane emissions will also change in the future.”

Original study

Oh, Y., Zhuang, Q., Liu, L., Welp, L.R., Lau, M.C.Y., Onstott, T.C., Medvigy, D., Bruhwiler, L., Dlugokencky, E.J., Hugelius, G., D’Imperio, L., Elberling, B., 2020. Reduced net methane emissions due to microbial methane oxidation in a warmer Arctic. Nature Climate Change, https://doi.org/10.1038/s41558-020-0734-z