Aggregate baselines for tropical peatland restoration and conservation projects

Baselines are a critical factor in peatland conservation or restoration projects in the voluntary carbon market, because a project's climate impact is measured by the difference between realised emissions and a baseline representing business-as-usual. Because business-as-usual encompasses a range of possible outcomes, the baseline is inherently uncertain. Baselines for peatland carbon projects present additional challenges because land use change at one location can drive greenhouse gas emissions elsewhere in the peatland. These effects occur because of the critical role of waterlogging in protecting peatland belowground carbon stocks, and imply that not only the area of land converted but also its spatial distribution exerts an important control on anthropogenic CO₂ emissions from peatlands.

To avoid bias and over-crediting, it is desirable to derive a baseline for peatland carbon projects that represents a weighted average across the range of possible outcomes, while considering the hydrological impacts of changing mosaics of land use on peatland greenhouse gas balances. We describe a pixel-matching approach to peatland baseline emissions that uses land use change modelling to produce an ensemble of land use trajectories collectively representing business-as-usual.  Emissions are then averaged across these realisations to produce an approximation of expected business-as-usual emissions.  We discuss the challenges involved in implementing this scheme while balancing rigor, simplicity, robustness and ease-of-use.