Climate change reduces the capacity of northern peatlands to absorb the atmospheric carbon dioxide: The different responses of bogs and fens

The carbon (C) storage of northern peatlands is equivalent to ~34–46% of the ~795 T g C currently held in the atmosphere as CO 2 . Most studies report that northern peatlands are a sink of between 20 and 60 g CO 2 –C m −2 yr −1 . Since peatland hydrology and biogeochemistry are very closely related to climate, there is concern whether northern peatlands will continue to function as C sinks with climate change. We used a coupled land surface scheme and peatland C model, called CLASS3W‐MWM, to examine the sensitivity of peatland C to climate change. Based on the data available to constrain our model, we simulated the C dynamics of the Mer Bleue (MB) bog in eastern Canada and the Degerö Stormyr (DS) poor fen in northern Sweden for four Intergovernmental Panel on Climate Change (IPCC) climate change scenarios, i.e., A1B, A2, B1, and Commit, over four time periods, i.e., present day, 2030, 2060, and 2100. When the simulated future C fluxes were compared to the baseline fluxes under the present climate conditions, we found that fens were much more sensitive to climate change than bogs. Gross primary production (GPP) at MB significantly increased by 4–44% up to 2100 for all scenarios except Commit. GPP at DS significantly decreased by 34–39% for A1B and A2, and slightly increased by 6–10% for B1 and Commit. Total ecosystem respiration (TER) significantly increased by 7–57% for MB and 4–34% for DS up to 2100 for all scenarios except Commit. Net ecosystem production (NEP), therefore, significantly decreased. The bog, however, was still a C sink up to 2100, though much reduced, but the fen switched to a C source for A1B and A2 scenarios. Additional experiments where we climatically transplanted the study peatlands or forced vegetation changes when the fen became too dry showed similar but less dramatic results as the standard runs. Our results indicate that northern peatlands should be included in the C‐coupled climate model to fully understand the response of C cycling in terrestrial ecosystems to climate change and to reduce the uncertainties for projecting the future climate.