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

Research output: Contribution to journalArticle

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 (CH4) emissions. Here, we quantify the thaw‐induced increase in CH4 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 (CO2) exchange. Using nested wetland and landscape eddy covariance net CH4 flux measurements in combination with flux footprint modeling, we find that landscape CH4 emissions increase with increasing wetland‐to‐forest ratio. Landscape CH4 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 CH4 emission of ~13 g CH4 m−2 is the dominating contribution to the landscape CH4 emission of ~7 g CH4 m−2. In contrast, forest contributions to landscape CH4 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 CH4 m−2 yr−1 in landscape CH4 emissions. A long‐term net CO2 uptake of >200 g CO2 m−2 yr−1 is required to offset the positive radiative forcing of increasing CH4 emissions until the end of the 21st century as indicated by an atmospheric CH4 and CO2 concentration model. However, long‐term apparent carbon accumulation rates in similar boreal forest‐wetland landscapes and eddy covariance landscape net CO2 flux measurements suggest a long‐term net CO2 uptake between 49 and 157 g CO2 m−2 yr−1. Thus, thaw‐induced CH4 emission increases likely exert a positive net radiative greenhouse gas forcing through the 21st century.

Details

Authors
  • Manuel Helbig
  • Laura Chasmer
  • Natascha Kljun
  • William L. Quinton
  • Claire C. Treat
  • Oliver Sonnentag
External organisations
  • University of Montreal, Canada
  • Wilfrid Laurier University
  • University of Alaska Fairbanks
  • United States Geological Survey Western Region
  • Swansea University
  • University of Lethbridge
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Climate Research
  • Environmental Sciences

Keywords

  • boreal forest, carbon dioxide, climate change, eddy covariance, methane, radiative forcing, wetland
Original languageEnglish
Pages (from-to)2413-2427
Number of pages15
JournalGlobal Change Biology
Volume23
Issue number6
Publication statusPublished - 2017
Publication categoryResearch
Peer-reviewedYes
Externally publishedYes