Peat carbon persistence and methane amplification under warming: explicit peatlands in UVic ESCM–WETMETH constrained by global targets

Peatlands are crucial for the regulation of the land carbon cycle and for the atmospheric methane budget. In Earth system models, improving wetland biogeochemistry and the representation of peat-specific processes has been shown to strengthen the realism of carbon-methane feedbacks and hence, the response of high-latitude land to climate warming in future simulation scenarios. We aimed to implement an explicit peatland representation in the University of Victoria Earth System Climate Model (UVic ESCM) by enhancing the WETMETH wetland methane framework to better account for the unique characteristics of peat soils and their associated carbon and methane cycling. The peatland development is based on two main components: (i) the integration of a high-resolution peatland distribution dataset (GPM 2.0) aggregated to the UVic ESCM grid using sub-cell fractional coverage, and (ii) the introduction of peatland-specific parameterizations within peat-designated grid cells to constrain key biogeochemical rates controlling long-term carbon storage and methane emissions. A 5000-year spin-up was carried to establish stable peat carbon and methane baselines, and two key peat-specific parameters were calibrated against independent global constraints.

The peatland configuration reproduces an equilibrium global peat carbon stock of 599.7 Pg C (target ≈600 Pg C) and a pre-industrial CH₄ concentration of 809.2 ppbv (target ≈808 ppbv), with negligible long-term drift. The implementation of explicit peatlands resulted shows, relative to a 1995–2015 baseline, global peat carbon changes are ~0%, 0%, −1%, and −1% by 2100 and ~0%, −4%, −12%, and −37% by 2300, for SSPs 1-2.6, 2-4.5, 4-6.0 and 5-8.5 respectively, while peatland methane emissions increase by ~+6%, +15%, +19%, and +37% by 2100 and ~+4%, +10%, +16%, and +54% by 2300. In summary, the explicit peatland implementation has successfully constrained peat carbon and methane to observationally consistent baselines, which now yield a robust peatland carbon-methane climate sensitivity and a reduced capacity of peatlands to retain carbon while amplifying their contribution to atmospheric methane under sustained warming.