Future northern peatland responses and its climate feedback under overshoot scenarios

Northern peatlands store 300~600 Pg carbon, with approximately half underlain by permafrost. Climate change is progressively threatening this large carbon stock. Future temperature rise is likely to trigger changes in this already vulnerable system and can cause irreversibility or strong hysteresis, increasing natural CO₂ and CH₄ emissions. However, the role of northern peatlands in carbon cycle under various future emission scenarios is still unclear. Elevated temperature and atmospheric CO₂ level may enhance the carbon sink in northern peatlands, while increased decomposition may lead to higher CO₂ emissions. At the same time, massive amount of CH₄ may be released due to permafrost thaw and other processes induced by future climate change.

The large carbon pool, as well as the often-delayed responses of northern peatlands, is an essential component in evaluating future climate responses, especially under overshoot scenarios. Ignoring the climate impact on this carbon pool may lead to misestimations of the carbon fluxes of terrestrial systems under future emission scenarios. Furthermore, it is critical to fully understand its feedback, which may make a significant contribution to the future carbon budget. Therefore, the role of peat carbon feedback in meeting the Paris Agreement goals must be investigated and quantified.

Significant progresses have been made in representing the northern peatlands with process-based complex land surface models. These results have laid a solid foundation to allow the development of our new peat carbon emulator. Compared to the extended run time required for complex land surface models, our emulator allows for running a large number of scenarios within a short time frame. The parameterizations of the peat carbon cycle, such as vegetation growth, soil carbon accumulation, organic matter decomposition, and CO₂ and CH₄ emissions are calibrated on five state-of-the-art complex land surface models that specifically represent high-latitude peatlands. By coupling the peat carbon emulator into the compact Earth System Model OSCAR, we incorporated the peatland feedback into global carbon-climate system and explored interactions between multiple feedbacks. Under a series of overshoot scenarios, we show that effective climate change mitigations are needed to prevent peat C loss and consequently positive climate feedback in the future.