Contrail prevention to reduce aviation’s non-CO2 climate impacts

The proposed methodology enables technology-based mitigation of atmospheric warming caused by aircraft contrail cirrus, which are clouds composed of ice crystal hydrometeors that act as short-lived climate forcers (SLCFs). When aircraft pass through cold and humid regions of the atmosphere (ice supersaturated regions or ISSRs), water vapour in the aircraft emissions triggers nucleation of ice hydrometeors that can persist for many hours, which collectively cause an annual net warming effect across all commercial flights. The draft methodology provides a process to mitigate contrail cloud radiative forcing by enabling modification of an existing flight plan to avoid ISSRs, which lead to persistent warming contrails. The net radiative impact mitigated is converted into CO2e, which is then converted into Certified Mitigation Outcome Units (CMOUs). CMOUs are not GS-VERs (carbon credits) and are not intended for use in the same way. This methodology is based on the best current scientific literature that is well established. However, this is a currently active research field, so as the science advances, changes will be made to the models within the methodology to keep them up to date with the state-of-the-art. The fundamentals of the methodology will not change, however, nor will the process detailed within the project boundary.