The aviation sector contributes to anthropogenic climate change through both CO 2 and non-CO 2 radiative effects. The CO 2 effect is considered to be much more certain than the non-CO 2 effects, yet there are relatively few studies that quantify it. Building on the scientific literature on burden sharing in the wake of the "Brazilian proposal", we discuss how to best attribute a fraction of the CO 2 radiative forcing to the aviation sector. For this we use the OSCAR compact Earth System model to estimate a contribution of aviation to the CO 2 concentration of 2.18 ppm in 2018. We further estimate the aviation contribution to the 2018 CO 2 radiative forcing to be 34.6, 32.6, 32.2 and 28.8 mW m − 2 for the proportional, differential, time-sliced and marginal methods, respectively. The time-sliced method has our preference because it is invariant upon disaggregation or recombination and can differentiate the relative impacts of early and late emissions. It leads to a radiative forcing estimate that is 12% larger than the residual method that is commonly used despite not being additive. This work has implications on the total-to-CO 2 RF ratio and the assessment of potential mitigation measures involving a trade-off between the CO 2 and non-CO 2 radiative effects of aviation.