Crediting peatland rewetting for carbon farming: Some considerations amidst optimism

Peatland drainage is worldwide a major human-induced greenhouse (GHG) source and rewetting increasingly considered a silver bullet to not only reverse the climate burden of peatland management, but also recover other ecosystem functions. Peatland rewetting is therefore one key measure in the evolving frameworks for carbon farming projects and an important nature based solution. However, with regards to the time horizon of rewetting projects and possible project failure the climate effect of rewetting has not yet been systematically analysed. Here we simulate the radiative forcing of peatland rewetting, based on impulse response functions, by using exemplary calculations addressing different time horizons, GHG fluxes and duration of project success. Water table drawdown during or after a rewetting project displaces GHG emissions into the future, meaning that rewetting projects that at some stage fail provide no climate benefit in the long run. This has important repercussions for the creditability of peatland projects and underpins that the value of peatland rewetting as a mitigation instrument strongly depends on successful and permanent implementation of a high water table. Furthermore, we show that linking radiative forcing with project duration and GHG emission patterns allows rational calculation of biophysical discounting and propose how such discounting can be used to account for the risk of project failure in payments to carbon farming schemes.