Review of methods for assessing the climate impacts of aviation technologies and the resulting best practices

The climate impact of aviation resulting from both CO₂ emissions and non-CO₂ effects is gaining attention from aviation stakeholders seeking to identify potential mitigation options. There is a need to consolidate the use of assessment methods and climate metrics, which are required to convert aviation non-CO₂ effects into CO₂ -equivalent emissions. We provide an overview of the operational, technological and scenario-based climate impact assessment methods that have been applied in literature as well as considerations and requirements for the choice of climate metric. We propose a four-layer technology climate impact assessment methodology, which includes: (1) the technology parameters, such as entry into service and temporal and spatial network use; (2) the calculation of three-dimensional aircraft trajectories and emission inventories; (3) the calculation of radiative forcing and induced temperature change time series; and (4) the overall climate impact, measured using a climate metric. We recommend two climate metrics that best fulfill the requirements, the Average Temperature Response (ATR100) and the Efficacy-weighted Global Warming Potential (EGWP100), both over 100 years. Additionally, we discuss further steps, such as the understanding of the most sensitive parameters in this approach, how uncertainties can be included to provide robust estimates, aspects of verification and update possibilities for new findings in research.