The social costs of aviation CO2 and contrail cirrus

The radiative forcing (RF) of contrail cirrus is substantial, though short-lived, uncertain, and heterogeneous, whereas the RF from CO₂ emissions is long-term and more predictable. To balance these impacts, we calculate the social costs of CO₂ and contrail cirrus using a modified Dynamic Integrated Climate Economy (DICE) model, spanning three discount rates, two damage functions, and three climate pathways. The main case estimate of the global social cost ratio of contrail cirrus to aviation CO₂ emissions ranges from 0.075 to 0.57, depending on assumptions. Accounting for uncertainty in contrail cirrus RF and climate efficacy further widens this range. We also quantify flight-specific social costs of contrail cirrus by analyzing nearly 500,000 flights over the North Atlantic, revealing substantial variability due to meteorological conditions. While uncertainty is considerable, our findings suggest that carefully implemented operational contrail avoidance could offer climate benefits even when the social cost of additional CO₂ emissions is considered.