Methane production as key to the greenhouse gas budget of thawing permafrost

• Published in: Nature climate change 2018-04, Vol.8 (4), p.309-312
• Main Authors: Knoblauch, Christian, Beer, Christian, Liebner, Susanne, Grigoriev, Mikhail N., Pfeiffer, Eva-Maria
• Format: Article
• Language: English
• Subjects: 704/106/125; 704/106/47; 704/47; Anoxia; Anoxic conditions; Carbon; Carbon dioxide; Carbon dioxide atmospheric concentrations; Climate; Climate Change; Climate Change/Climate Change Impacts; Decomposition; Earth and Environmental Science; Environment; Environmental Law/Policy/Ecojustice; Feedback; Gases; Global warming; Greenhouse effect; Greenhouse gases; Letter; Melting; Methane; Methane production; Microbial activity; Microorganisms; Organic carbon; Oxic conditions; Permafrost; Positive feedback; Thawing
• ISSN: 1758-678X; 1758-6798; 1758-6798
• DOI: 10.1038/s41558-018-0095-z

Permafrost thaw liberates frozen organic carbon, which is decomposed into carbon dioxide (CO 2 ) and methane (CH 4 ). The release of these greenhouse gases (GHGs) forms a positive feedback to atmospheric CO 2 and CH 4 concentrations and accelerates climate change 1 , 2 . Current studies report a minor importance of CH 4 production in water-saturated (anoxic) permafrost soils 3 – 6 and a stronger permafrost carbon–climate feedback from drained (oxic) soils 1 , 7 . Here we show through seven-year laboratory incubations that equal amounts of CO 2 and CH 4 are formed in thawing permafrost under anoxic conditions after stable CH 4 -producing microbial communities have established. Less permafrost carbon was mineralized under anoxic conditions but more CO 2 –carbon equivalents (CO 2 –Ce) were formed than under oxic conditions when the higher global warming potential (GWP) of CH 4 is taken into account 8 . A model of organic carbon decomposition, calibrated with the observed decomposition data, predicts a higher loss of permafrost carbon under oxic conditions (113 ± 58 g CO 2 –C kgC −1 (kgC, kilograms of carbon)) by 2100, but a twice as high production of CO 2 –Ce (241 ± 138 g CO 2 –Ce kgC −1 ) under anoxic conditions. These findings challenge the view of a stronger permafrost carbon-climate feedback from drained soils 1 , 7 and emphasize the importance of CH 4 production in thawing permafrost on climate-relevant timescales. An organic carbon decomposition model, calibrated with laboratory incubations, indicates a greater production rate of CO 2 -C equivalents from waterlogged (compared to drained) permafrost soils, when the higher global warming potential of methane is factored in.