SPRUCE-MIP: Model Intercomparison of Northern Peatland Carbon Cycle Over the SPRUCE Site

Peatlands cover only 3% of Earth’s land surface but contain about 30% of the global soil carbon pool. The strong sensitivity of C cycle to environmental factors such as soil temperature and moisture has let to concerns about potential positive feedbacks to climate change. However, global models disagree as to the magnitude and spatial distribution of emissions, partially due to missing representations of peatland relevant processes and a scarcity of in situ observations. The Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment is a large‐scale climate change manipulation that focuses on the combined response of multiple levels of warming at both ambient and elevated CO₂ concentration (eCO₂), making it a valuable testbed for the broader modeling community to improve the diagnosis and attribution of C fluxes in peatland ecosystems. Currently, there are 11 models participating in the SPRUCE Model Intercomparison Project (SPRUCE-MIP). In the first stage, all model groups used observed ambient plot atmospheric forcing data to drive a model spin-up simulation with pre-industrial conditions, and a transient simulation with transient atmospheric CO₂ concentrations and nitrogen deposition from 1850 to 2014. Then, measured plot-level meteorological forcing and CO₂ concentrations from the 10 treatment enclosures and the ambient plot drove 11 transient simulations from 2015 to 2021. The total of 11 simulations represents five levels of temperature treatment with two CO₂ levels, and ambient control plot with no enclosure. The five treatment temperatures are +0, 2.25, 4.5, 6.75, 9^oC, and the two CO₂ levels are ambient and +500 ppm. We evaluated the performance of multiple models against SPRUCE observations, such as the net ecosystem exchange (NEE) and CH₄ fluxes warming responses under ambient and eCO₂ conditions and found that there were wide spreads for warming responses among different models. We will further evaluate the model performances and quantify the associated uncertainties, which may have helpful implications for our understanding of the peatland C cycle and for future projections of Earth system models.