Large stocks of peatland carbon and nitrogen are vulnerable to permafrost thaw

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 117; no. 34; pp. 20438 - 20446
• Main Authors: Hugelius, Gustaf, Loisel, Julie, Chadburn, Sarah, Jackson, Robert B., Jones, Miriam, MacDonald, Glen, Marushchak, Maija, Olefeldt, David, Packalen, Maara, Siewert, Matthias B., Treat, Claire, Turetsky, Merritt, Voigt, Carolina, Yu, Zicheng
• Format: Journal Article
• Language: English
• Published: Washington National Academy of Sciences 25.08.2020
• Series: From the Cover
• Subjects: Anthropogenic factors; Carbon dioxide; carbon stocks; Climate change; Emissions; Global warming; Greenhouse effect; greenhouse gas fluxes; Greenhouse gases; Learning algorithms; Machine learning; Methane; Nitrogen; nitrogen stocks; Nitrous oxide; northern peatlands; Organic carbon; Peat; Peatlands; Permafrost; permafrost thaw; Permafrost thaws; Physical Sciences; Radiative forcing; Spatial distribution
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1916387117

Northern peatlands have accumulated large stocks of organic carbon (C) and nitrogen (N), but their spatial distribution and vulnerability to climate warming remain uncertain. Here, we used machine-learning techniques with extensive peat core data (n > 7,000) to create observation-based maps of northern peatland C and N stocks, and to assess their response to warming and permafrost thaw. We estimate that northern peatlands cover 3.7 ± 0.5 million km² and store 415 ± 150 Pg C and 10 ± 7 Pg N. Nearly half of the peatland area and peat C stocks are permafrost affected. Using modeled global warming stabilization scenarios (from 1.5 to 6 °C warming), we project that the current sink of atmospheric C (0.10 ± 0.02 Pg C·y−1) in northern peatlands will shift to a C source as 0.8 to 1.9 million km² of permafrost-affected peatlands thaw. The projected thaw would cause peatland greenhouse gas emissions equal to ∼1% of anthropogenic radiative forcing in this century. The main forcing is from methane emissions (0.7 to 3 Pg cumulative CH4-C) with smaller carbon dioxide forcing (1 to 2 Pg CO2-C) and minor nitrous oxide losses. We project that initial CO2-C losses reverse after ∼200 y, as warming strengthens peatland C-sinks. We project substantial, but highly uncertain, additional losses of peat into fluvial systems of 10 to 30 Pg C and 0.4 to 0.9 Pg N. The combined gaseous and fluvial peatland C loss estimated here adds 30 to 50% onto previous estimates of permafrost-thaw C losses, with southern permafrost regions being the most vulnerable.