Aviation climate impact and opportunities for mitigation

Licentiate thesis, 2026

Climate impact from aviation is an ever-growing concern, driven by the continued increase in air traffic and associated emissions. The climate impact extends beyond carbon dioxide (CO₂), with non-CO₂ emissions and contrail formation together constituting a substantial share of the sector’s total anthropogenic radiative forcing. This thesis develops methods to evaluate the different contributions to aviation-induced climate impact, with particular emphasis on non-CO₂ effects. It then describes the metrics used to compare emissions with fundamentally different characteristics. Mitigation pathways aimed at reducing aviation’s overall climate footprint are evaluated. Special focus is placed on contrails, which represent a highly variable but potentially dominant component of aviation’s climate impact and offer opportunities for mitigation through targeted operational measures. The climate impact of Swedish aviation is assessed and attributed to individual emission species, highlighting the significant contribution of non-CO₂ effects and the strong spatial, temporal, and seasonal variability of contrail formation. The results indicate that a relatively small subset of flights is responsible for a disproportionate share of contrail-induced warming, suggesting that selective contrail avoidance strategies could yield substantial climate benefits with limited operational disruption and cost. In addition to operational measures, this thesis investigates technological solutions, with a detailed analysis of the Water Enhanced Turbofan (WET) engine concept, which has been proposed as a means to reduce fuel burn as well as emissions of nitrogen
oxides (NO_x ) and contrails. The performance and thermodynamic constraints of the WET engine are evaluated, showing that installation effects may offset its previously predicted advantages. Overall, the findings in this thesis underscore the importance of addressing non-CO₂ effects in aviation climate assessments and demonstrate that both targeted operational strategies and careful evaluation of emerging technologies are essential for achieving meaningful reductions in the sector’s climate impact.