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Abstract Northern peatlands have been a carbon sink since their initiation. This has been simulated by existing process‐based models. However, most of these models are limited by lacking sufficient processes of the N cycle in peatlands. Here, we use a peatland biogeochemistry model incorporated with N‐related processes of fixation, deposition, gas emission, loss through water flow, net mineralization, plant uptake and litterfall to project the role of the peatlands in future radiative forcing (RF). Simulations from 15‐ka BP to 2100 are conducted driven by CMIP5 climate forcing data of IPSL‐CM5A‐LR and bcc‐csm1‐1, including warming scenarios of RCP 2.6, RCP 4.5 and RCP 8.5. During the Holocene, northern peatlands have an increasing cooling effect with RF up to −0.57 W m⁻². By 1990, these peatlands accumulate 408 Pg C and 7.8 Pg N. Under warming, increasing mineral N content enhances plant net primary productivity; the cooling effect persists. However, RF increases by 0.1–0.5 W m⁻²during the 21st century, mainly due to the stimulated CH₄emissions. Northern peatlands could switch from a C sink to a source when the annual temperature exceeds −2.2 to −0.5°C. This study highlights that the improved N cycle causes higher CO₂‐C sink capacity in northern peatlands. However, it also causes a significant increase in CH₄emissions, which weakens the cooling effect of northern peatlands in future climate. 

Abstract. Northern peatlands have been a large C sink during the Holocene,but whether they will keep being a C sink under future climate change isuncertain. This study simulates the responses of northern peatlands tofuture climate until 2300 with a Peatland version Terrestrial EcosystemModel (PTEM). The simulations are driven with two sets of CMIP5 climate data(IPSL-CM5A-LR and bcc-csm1-1) under three warming scenarios (RCPs 2.6, 4.5 and8.5). Peatland area expansion, shrinkage, and C accumulation anddecomposition are modeled. In the 21st century, northern peatlands areprojected to be a C source of 1.2–13.3 Pg C under all climate scenariosexcept 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-LRscenarios, being larger sources than bcc-csm1-1 scenarios (5.9–118.3 vs.0.7–87.6 Pg C). C sources are attributed to (1) the peatland water table depth(WTD) becoming deeper and permafrost thaw increasing decomposition rate; (2) net primary production (NPP) not increasing much as climate warms becausepeat drying suppresses net N mineralization; and (3) as WTD deepens,peatlands switching from moss–herbaceous dominated to moss–woody dominated,while woody plants require more N for productivity. Under IPSL-CM5A-LRscenarios, northern peatlands remain as a C sink until the pan-Arctic annualtemperature reaches −2.6 to −2.89 ∘C, while this threshold is −2.09to −2.35 ∘C under bcc-csm1-1 scenarios. This study predicts anorthern peatland sink-to-source shift in around 2050, earlier than previousestimates of after 2100, and emphasizes the vulnerability of northernpeatlands to climate change. 

Abstract Wildfires are a major disturbance to forest carbon (C) balance through both immediate combustion emissions and post-fire ecosystem dynamics. Here we used a process-based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), to simulate C budget in Alaska and Canada during 1986–2016, as impacted by fire disturbances. We extracted the data of difference Normalized Burn Ratio (dNBR) for fires from Landsat TM/ETM imagery and estimated the proportion of vegetation and soil C combustion. We observed that the region was a C source of 2.74 Pg C during the 31-year period. The observed C loss, 57.1 Tg C year −1 , was attributed to fire emissions, overwhelming the net ecosystem production (1.9 Tg C year −1 ) in the region. Our simulated direct emissions for Alaska and Canada are within the range of field measurements and other model estimates. As burn severity increased, combustion emission tended to switch from vegetation origin towards soil origin. When dNBR is below 300, fires increase soil temperature and decrease soil moisture and thus, enhance soil respiration. However, the post-fire soil respiration decreases for moderate or high burn severity. The proportion of post-fire soil emission in total emissions increased with burn severity. Net nitrogen mineralization gradually recovered after fire, enhancing net primary production. Net ecosystem production recovered fast under higher burn severities. The impact of fire disturbance on the C balance of northern ecosystems and the associated uncertainties can be better characterized with long-term, prior-, during- and post-disturbance data across the geospatial spectrum. Our findings suggest that the regional source of carbon to the atmosphere will persist if the observed forest wildfire occurrence and severity continues into the future.