The role of northern peatlands in the global carbon cycle for the 21st century

Aim: Persistent sinks of atmospheric CO₂ in undisturbed peatlands are not included in future projections of the global carbon budget. We aimed to explore possible responses of northern peatlands to future climate change and to quantify the role of northern peatlands in the carbon balance of the Northern Hemisphere. Location: The terrestrial Northern Hemisphere (>30° N). Time period: 1861–2099. Major taxa studied: Not a specific plant species, but a plant functional type is used by the model to represent an average of all vegetation growing in northern peatlands. Methods: The ORCHIDEE-PEAT v.2.0 process-based land surface model was used to simulate area and carbon dynamics of northern peatlands. The model was driven up to the year 2099 by the global CO₂ concentration from representative concentration pathways (RCPs) 2.6, 6.0 and 8.5 by corresponding climate projections from two general circulation models after bias correction. Results: First, from 1861 to 2005 the mean annual carbon balance of northern peatlands was an atmospheric CO₂ sink of 0.10 PgC/year, and this sink will roughly double in the future under both RCP2.6 and RCP6.0, whereas the total northern peatlands will be either a source of CO₂ (IPSL-CM5A-LR) or near neutral (GFDL-ESM2M) by the end of the century under RCP8.5. Second, the peatlands in western Canada, western and northern Europe may experience reducing areas and may shift from being CO₂ sinks to sources, especially under rapid climate warming. Third, peatland enhances soil carbon accumulation in the Northern Hemisphere (lands north of 30° N). Main conclusions: In this study, future changes in both northern peatland extent and peatland carbon storage are simulated. We highlight that undisturbed northern peatlands are small but persistent carbon sinks in the future; thus, it is important to protect these ecosystems.