The compact Earth system model OSCARv2.2 is used to assess the climate impact of present and future civil aviation carbon dioxide (CO₂) emissions. The impact of aviation CO₂ on future climate is quantified over the 1940–2050 period, extending some simulations to 2100 and using different aviation CO₂ emission scenarios and two background Representative Concentrations Pathways (RCP2.6 and RCP6.0) for other emission sectors. Several aviation scenarios including weak to strong mitigation options are considered with emissions ranging from 386 MtCO₂/year (Factor 2 scenario) to 2338 MtCO₂/year (ICAO based scenario) in 2050. As a reference, in 2000, the calculated impact of aviation CO₂ emissions is 9.1 ± 2 mK (0.8% of the total anthropogenic warming associated to fossil fuel emissions). In 2050, on a climate trajectory in line with the Paris Agreement limiting the global warming below 2 °C (RCP2.6), the impact of the aviation CO₂ emissions ranges from 26 ± 2 mK (1.4% of the total anthropogenic warming associated to fossil fuel emissions) for an ambitious mitigation strategy scenario (Factor 2) to 39 ± 4 mK (2.0% of the total anthropogenic warming associated to fossil fuel emissions) for the least ambitious mitigation scenario of the study (ICAO based). On the longer term, if no significant emission mitigation is implemented for the aviation sector, the associated warming could further increase and reach a value of 99.5 mK ± 20 mK in 2100 (ICAO based), which corresponds to 5.2% of the total anthropogenic warming under RCP2.6. The contribution of CO₂ is estimated to represent 36%–51% of the total aviation radiative forcing of climate including short-term climate forcers. However, due to its long residence time in the atmosphere, aviation CO₂ will have a major contribution on decadal time scales. These additional short-terms forcers are subject to large uncertainties and will be analysed in forthcoming studies.

The contribution of aircraft operations to ambient ultrafine particle (UFP) concentration at and around airports can be significant. This review article considers the volatile and non-volatile elements of particulate matter emissions from aircraft engines, their characteristics and quantification and identifies gaps in knowledge. The current state of the art emission inventory methods and dispersion modelling approaches are reviewed and areas for improvement and research needs are identified. Quantification of engine non-volatile particulate matter (nvPM) is improving as measured certification data for the landing and take-off cycle are becoming available. Further work is needed: to better estimate nvPM emissions during the full-flight; to estimate non-regulated (smaller) engines; and to better estimate the emissions and evolution of volatile particles (vPM) in the aircraft exhaust plume. Dispersion modelling improvements are also needed to better address vPM. As the emissions inventory data for both vPM and nvPM from aircraft sources improve, better estimates of the contribution of aircraft engine emissions to ambient particulate concentrations will be possible.

When working towards regulation of supersonic aviation, a comprehensive understanding of the global climate effect of supersonic aviation is required in order to develop future regulatory issues. Such research requires a comprehensive overview of existing scientific literature having explored the climate effect of aviation. This review article provides an overview on earlier studies assessing the climate effects of supersonic aviation, comprising non-CO₂ effects. An overview on the historical evaluation of research focussing on supersonic aviation and its environmental impacts is provided, followed by an overview on concepts explored and construction of emission inventories. Quantitative estimates provided for individual effects are presented and compared. Subsequently, regulatory issues related to supersonic transport are summarised. Finally, requirements for future studies, e.g., in emission scenario construction or numerical modelling of climate effects, are summarised and main conclusions discussed.

The climate impact of aviation resulting from both $$\text {CO}_2$$ emissions and $$\text {non-CO}_2$$ 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 $$\text {non-CO}_2$$ effects into $$\text {CO}_2$$ -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.

Contrails affect the radiative balance of the Earth climate (Lee et al., 2021). The representation of contrails characteristics and evolution into climate model remains highly challenging due to the complexity of the microphysical and chemical processes involved into the formation of contrails. The high sensitivity of contrails Radiative Forcing (RF) to the contrails morphology and composition in terms of ice crystal shape, number and size as well as surface temperature and albedo leads to major uncertainty when the RF of contrails is evaluated. In this paper, contrails RF has been modelled using the CEDRE-ASTRE Monte Carlo solver (Tessé and Lamet, 2011) for 1D and 2D idealized representations of a contrail in an atmospheric column (0 - 120 km). The role of the microphysical contrail characteristics have been evaluated using a multiple run sensitivity analysis to key parameters in the determination of contrails RF such as ice crystal size, ice water content, surface albedo and emissivity. A critical analysis of the results is made with comparable studies using different codes (Wolf et al., 2023) and will be detailed in the presentation. References Lee, D.S., Fahey, D.W., Skowron, A., Allen, M.R., Burkhardt, U., Chen, Q., Doherty, S.J., Freeman, S., Forster, P.M., Fuglestvedt, J., Gettelman, A., De León, R.R., Lim, L.L., Lund, M.T., Millar, R.J., Owen, B.,Penner, J.E., Pitari, G., Prather, M.J., Sausen, R., Wilcox, L.J., The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018, Atmospheric Environment, 2021, 244.Tessé L. and Lamet J.-M., Radiative Transfer Modeling Developed at ONERA for Numerical Simulations of Reactive Flows, AerospaceLab, ed. 2, https://aerospacelab.onera.fr/en/Radiative-Transfer-Modeling-Developed, 2011.Wolf, K., Bellouin, N., and Boucher, O.: Sensitivity of cirrus and contrail radiative effect on cloud microphysical and environmental parameters, Atmos. Chem. Phys., 23, 14003–14037, https://doi.org/10.5194/acp-23-14003-2023, 2023.