Measures of effectiveness to compare the climate mitigation potential of afforestation and BECCS

The climate mitigation potential of terrestrial carbon dioxide removal (CDR) methods remains highly uncertain depending on the timing and magnitude of climate mitigation but also due to model uncertainty in the underlying Earth System models. In addition to these uncertainties, there are different approaches to measuring the effectiveness of CDR methods for climate change mitigation. In our study, we introduce various measures of effectiveness and evaluate the climate mitigation potential of afforestation and bioenergy plants under the low-emission scenario ssp126. To do this, we use the land component JSBACH3 of the Earth System Model MPI-ESM; afforestation is represented as the spatial increase of four forest plant functional types. Bioenergy plants are represented as highly efficient C4 plants (miscanthus and panicum). There are various assumptions concerning fossil fuel substitution and carbon capture and storage. Measuring effectiveness over time, we show how bioenergy plants become more effective over the long term compared to afforestation. In addition to this temporal measure, the climate mitigation potential of bioenergy plants depends significantly on the rate of fossil fuel substitution. Lastly, the spatial extent that is needed to match a given CDR amount in time by afforestation and BECCS can be quantified. Our study thus asses and compares the potentials of the two CDR methods highlighting the various perspectives of assessment.