Hot or not – How do we want to rate the climate effects of peatland rewetting?

The climate effect accomplished through peatland rewetting is primarily assessed via the global warming potential (GWP), as it evolves from the emissions of greenhouse gases CO2 and CH4. The GWP aggregates the various radiative efficiencies and atmospheric lifetimes of the involved greenhouse gases into a single metric and forms the base of existing accounting approaches to incorporate peatland-based land use measures in climate reporting under LULUCF.Building on the work of Neubauer and Megonigal (2015) on the relevance of the continuous emission behavior of peatlands, we propose additional metrics based on the radiative forcing (RF) dynamics that occur after rewetting. These metrics, unlike GWP, are not tied to fixed reference time horizons and can add further aspects to the climate assessment of rewetting:The switch over time: the time when the net RF trajectory approaches zero, which marks the turning point for the peatland to exert a net cooling effect Total radiative forcing: the total heat energy released until switch over time is reached. Pay-off time: the time when mitigation effects occur, i.e., a rewetting measure becomes climatically beneficial compared to ongoing drainage as business-as-usual land use scenario. The pay-off time requires emission data from the drainage state, but can also be estimated in reference to established inventory approaches such as Tiemeyer et al. (2020). Our literature review revealed that most rewetted peatlands fall in one out of three main categories: (i) cases with instant mitigation effects that exert a net cooling effect within few decades (ii) cases where mitigation is reached within 10-20 years, but cause persistent warming, and (iii) cases in which mitigation is unlikely to be achieved.  We want to discuss, whether the metrics introduced can be a scientifically substantiated and intuitive complement to the established GWP. We think, that our approach can further structure and facilitate the communication on the climate prospects of peatland rewetting. A systematic analysis of available literature values within the assessment framework presented can help to prioritize implementation actions and tailor future research activities.ReferencesNeubauer, Scott C., and J. Patrick Megonigal. "Moving beyond global warming potentials to quantify the climatic role of ecosystems." Ecosystems 18.6 (2015): 1000-1013.Tiemeyer, Bärbel, et al. "A new methodology for organic soils in national greenhouse gas inventories: Data synthesis, derivation and application." Ecological Indicators 109 (2020): 105838.