## 3 Results
### Comparison of Climate- and Fuel-Optimised Configurations  
Table 1 summarises the major differences between the fuel-optimised and the climate-optimised set-up of ISO compared to the non-stop reference. The comparison reveals the following major differences with regards to the share of beneficial ISO missions, distance and flight time as well as fuel consumption and emissions. An implementation of the ISO concept with the set boundary conditions in terms of possible flight level and airports is beneficial for approximately half of all missions from a fuel-optimising perspective (48.23%), while climate impact can be reduced for almost all missions (99.98%). Fuel-optimised ISO starts to come into effect at stage lengths of 6300 km and above, while it can be beneficial from a climate-perspective for all observed flight lengths. Moreover, it has to be noted that this is not only due to an implementation of the ISO concept itself, but also due to the considered reduction in flight altitudes in the climate-optimised set-up.  
In the fuel-optimised context, we observe small additional flight distances due to a preference of intermediate stop airports associated with minimum detour and eccentricity. An intermediate refuelling stop is only performed in those cases where an airport with a small detour is available, so that we see an average detour of 0.04%. By contrast, the climate-optimised set-up accepts higher detour (on average + 3.58%) and eccentricity parameters associated with the selected intermediate stop airports if, in turn, climate-sensitive areas can be avoided. While in the fuel optimised set-up, approximately two thirds (63.5%) of all ISO missions are associated with an offset factor below 0.575, we observe a broader distribution for the climate-optimised ISO flights (22.5% below 0.575 offset factor). Consequently, we observe longer flight times in the climate-optimised case due to larger detours as well the higher share of intermediate landings and the associated on-ground times.  
Figure 5: Change in ATR100 per emission species for climate-optimised ISO compared to the non-stop reference case.  
With ISO, fuel consumption can be reduced by 1.9% for the sample of this study. This also reduces total emission quantities for CO\({}_{2}\), H\({}_{2}\)O, and NO\({}_{\rm x}\). Restricting the analysis to missions where ISO is beneficial from a fuel-efficiency perspective, fuel consumption can be decreased by 3.2%. Conversely, the required fuel and emission quantities increase for the climate-optimised scenario caused by longer flight distances and reduced cruise altitudes.  
The climate impact in terms of ATR100 increases by 0.64% in the fuel-optimised case, although overall emission quantities decrease. ATR20 changes equivalently (+0.61%). This can be explained with higher emission altitudes. Therefore, climate impact from non-CO\({}_{2}\) emissions rises in comparison to the non-stop reference case: in particular, climate impact induced by nitrogen oxides rises (+2.8% in ATR100) as well as water vapour, (+11.7%) and this overcompensates the reduction caused by decreased CO\({}_{2}\) emissions (\(-\)1.9%) and contrail cirrus (\(-\)2.7%).  
In addition to the above-mentioned points, the location of intermediate stop airports as well as the selected cruise flight level vary significantly between the fuel-optimised and climate-optimised scenarios. This impacts the resulting mitigation potentials. Figure 6 shows the zonal and vertical distributions of CO\({}_{2}\) emissions for both cases. A shift to lower altitudes and latitudes by the climate optimisation is hypothesised and further analysed in the following.