The positive net radiative greenhouse gas forcing of increasing methane emissions from a thawing boreal forest‐wetland landscape

• Published in: Global Change Biology
• Main Authors: Helbig, Manuel, Chasmer, Laura E., Kljun, NatasCha, Quinton, William L., Treat, Claire C., Sonnentag, Oliver
• Other Authors: Fonds de Recherche du Québec - Nature et Technologies, Deutscher Akademischer Austauschdienst, Canada Research Chairs, Canada Foundation for Innovation, Natural Sciences and Engineering Research Council of Canada, National Science Foundation
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2016
• Subjects: Canada; Peat; permafrost; taiga; Taiga plains
• Online Access: http://dx.doi.org/10.1111/gcb.13520; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fgcb.13520; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.13520; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/gcb.13520; https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/gcb.13520

Abstract At the southern margin of permafrost in North America, climate change causes widespread permafrost thaw. In boreal lowlands, thawing forested permafrost peat plateaus (‘forest’) lead to expansion of permafrost‐free wetlands (‘wetland’). Expanding wetland area with saturated and warmer organic soils is expected to increase landscape methane (CH 4 ) emissions. Here, we quantify the thaw‐induced increase in CH 4 emissions for a boreal forest‐wetland landscape in the southern Taiga Plains, Canada, and evaluate its impact on net radiative forcing relative to potential long‐term net carbon dioxide (CO 2 ) exchange. Using nested wetland and landscape eddy covariance net CH 4 flux measurements in combination with flux footprint modeling, we find that landscape CH 4 emissions increase with increasing wetland‐to‐forest ratio. Landscape CH 4 emissions are most sensitive to this ratio during peak emission periods, when wetland soils are up to 10 °C warmer than forest soils. The cumulative growing season (May–October) wetland CH 4 emission of ~13 g CH 4 m −2 is the dominating contribution to the landscape CH 4 emission of ~7 g CH 4 m −2 . In contrast, forest contributions to landscape CH 4 emissions appear to be negligible. The rapid wetland expansion of 0.26 ± 0.05% yr −1 in this region causes an estimated growing season increase of 0.034 ± 0.007 g CH 4 m −2 yr −1 in landscape CH 4 emissions. A long‐term net CO 2 uptake of >200 g CO 2 m −2 yr −1 is required to offset the positive radiative forcing of increasing CH 4 emissions until the end of the 21st century as indicated by an atmospheric CH 4 and CO 2 concentration model. However, long‐term apparent carbon accumulation rates in similar boreal forest‐wetland landscapes and eddy covariance landscape net CO 2 flux measurements suggest a long‐term net CO 2 uptake between 49 and 157 g CO 2 m −2 yr −1 . Thus, thaw‐induced CH 4 emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century.