Table 1 Summary of the advantages and disadvantages of the GHG perturbation model and CO₂-e.q. metrics

GHG perturbation model

The GHG perturbation model facilitates understanding of the temporal pattern of wetland GHG fluxes, which benefit the identification of the radiative forcing switchover time (i.e., the length of time after which the warming effect due to CH₄ emissions is overtaken by the cumulative removal [cooling effect] of CO₂) associated with wetland state conversion^20,33.

The GHG perturbation model assumes wetland CO₂ and CH₄ fluxes to be constant over time, but they vary as a function of climatic variability and climate change³¹. Note: the limitation associated with the GHG perturbation model also applies to CO₂-e.q. metrics.

GWP

The GWP metric is easy to implement. The 100-year variant of the Global Warming Potential (GWP₁₀₀) has been formally adopted in international climate policy (e.g., Paris Agreement, Kyoto Protocol) and have become the standard for expressing emissions in the scientific literature and general media^15,24.

The GWP metric considers GHG emissions as a single pulse while ecosystem emissions are usually continuous throughout time^24,27.

The GWP metric does not consider the difference in atmospheric lifetime between CO₂ and CH₄, which has led to overestimation on cumulative effect of wetland CH₄ on total warming and resulted in incorrect conclusions on the climatic role of wetland ecosystems^24,27.

The GWP metric needs to be applied over a predefined period that is arbitrary and disconnected from policy timelines²⁴.

SGWP

The SGWP metric is easy to implement. The SGWP metric considers the sustained behaviour of wetland GHG fluxes by treating wetland GHG emissions as persistent – and not one time – events¹⁵.

Like the GWP metric, the SGWP metric needs to be applied over a predefined period and therefore do not adequately capture the climate role of wetland GHG emissions¹⁵.

GWP*

The GWP* metric allows for the generation of dynamic CO₂-e.q. carbon budget over any timeframe of interest following wetland state conversion and do not need to be applied over a predefined period. The GWP* metric has been shown to better track the temperature impacts of the integrated radiative forcing associated with CH₄ emissions^22,23.

Unlike the predefined period metrics (i.e., GWP and SGWP), the GWP* metric does not allow for direct conversion of wetland GHG emissions to CO₂-e.q. format. The GWP* metric requires the GHG emission profile over the 20-years preceding any value, as it considers a 20-year running average^23,27. This requirement could potentially complicate broad implementation of the GWP* metric.