The climate impacts of aviation policy cannot be determined exactly. There are three types of uncertainties that arise at different points in the impact assessment:

• Future uncertainty: SCBAs typically consider a period of 50 to 100 years. However, future demand for aviation, available airport capacity, technological developments and global warming cannot be accurately predicted. Future uncertainties are usually overcome in SCBAs by calculating effects for different future scenarios;
• Policy uncertainty: National and international policies regarding aviation and the climate are also uncertain. A more ambitious international climate policy for instance means that additional national policies have less effect (and vice versa). Policy uncertainties can be captured with sensitivity analyses;
• Knowledge uncertainties: Finally, there are multiple knowledge uncertainties, simply because certain effects cannot (yet) be precisely estimated based on existing models and knowledge. Knowledge uncertainties can also be overcome through sensitivity analyses.

The greatest (knowledge) uncertainty concerns the warming effect of non-CO₂ components, particularly those of contrails and nitrogen (NO_x). This is because: (1) the warming effect of non-CO₂ components is still mainly based on a limited number of models and expert judgment, (2) certain processes in the atmosphere are not yet well understood, and (3) the warming effect of different components depends on multiple factors, including lifetime, location, time and altitude.

Because of these uncertainties, the warming effect of non-CO₂ is tentatively derived from the effect of CO₂ in Dutch SCBAs using a multiplier. The contribution of non-CO₂ to the total climate impact of aviation is likely to decrease over time. Regulation and technological developments are causing non-CO₂ components to become less prevalent. This will have a direct effect on limiting warming because of the limited lifetime of non-CO₂. This is in contrast to CO₂, which continues to contribute to warming even hundreds to thousands of years after emission. If the contribution of non-CO₂ to the climate effect decreases, then the multiplier for non-CO₂ in SCBAs will also have to decrease over time.