Why lightweight climate models are useful tools for assessing aviation mitigation strategies and moving beyond the CO2-equivalence metrics debate

Abstract Assessing mitigation strategies for aviation is a critical issue for the aviation ecosystem stakeholders, while the debate continues on the most appropriate CO₂-equivalence metrics to address non-CO₂. This paper proposes two lightweight climate models that can be parameterised to assess these strategies and move beyond the CO₂-equivalence metrics debate. A first approach relies on the use of the GWP* method, calibrated in an original manner, for estimating warming equivalent emissions. A second approach employs the FaIR climate emulator. These lightweight models, which should be considered as a new family of climate models for aviation facilitating parametric studies, provide a straightforward and consistent means of evaluating mitigation strategies at the temperature level, bypassing the need for CO₂-equivalence metrics for comparing strategies. The latter should rather be used in policy mechanisms to encourage the emergence of strategies (once justified by the climate models), as they are not suitable for assessing temperature changes from aviation. The debate on the choice of CO₂-equivalence metrics could then focus on methodological and ethical criteria. Nonetheless, this paper demonstrates that the higher the traffic, the more appropriate it is to choose CO₂-equivalence metrics with high values for consistency with temperature estimates.