Comment on egusphere-2022-1006

Abstract

Northern peatlands are a large C sink during the Holocene, but whether they will keep being a C sink under future climate change is uncertain. This study simulates the responses of northern peatlands to future climate until 2300 with a Peatland version Terrestrial Ecosystem Model (PTEM). The simulations are driven with two sets of CMIP5 climate data (IPSL-CM5A-LR and bcc-csm1-1) under three warming scenarios (RCP2.6, 4.5 and 8.5). Peatlands expansion, shrink, accumulation and decomposition are modeled. In the 21st century, northern peatlands are projected to be a C source of 1.2–13.3 Pg C under all climate scenarios except for RCP 2.6 of bcc-csm1-1 (a sink of 0.8 Pg C). During 2100–2300, northern peatlands under all scenarios are a C source under IPSL-CM5A-LR scenarios, being larger sources than bcc-csm1-1 scenarios (5.9–118.3 vs. 0.7–87.6 Pg C). The peatland being C sources are due to: 1) water table depth (WTD) becomes deeper and permafrost thaw increases decomposition rate; 2) net primary production (NPP) does not increase much as climate warms because peat drying suppresses net N mineralization and 3) as WTD deepens, peatlands switches from moss-herbaceous dominated to moss-woody dominated, while woody plants require more N for productivity. Under IPSL-CM5A-LR scenarios, northern peatlands remain as a C sink until pan-Arctic annual temperature reaches -2.6–-2.89°C, while this threshold is -2.09–-2.35°C under bcc-csm1-1 scenarios. This study predicts an earlier northern peatland sink to source shift than previous estimates in the literature and emphasizes the vulnerability of northern peatlands to climate change.