Contrail cirrus net radiative forcing due to an 80% reduced initial ice crystal number. Hatched areas indicate locations in which the difference is statistically significant at a 95% confidence level. Source: German Aerospace Center

Aviation makes a significant contribution to anthropogenic climate forcing in the form of soot, aerosol and greenhouse gas emissions. Soot emissions are responsible for the formation of cirrus contrails composed of ice crystals that can trigger climate warming effects.

The increased use of biomass-based aviation fuels can reduce soot emissions and subsequent contrail formation, according to analyses conducted by German Aerospace Center researchers. An 80% reduction in soot-related ice crystal formation associated with the use of a 50:50 blend of biofuel and Jet A aviation fuel can halve the climate impact of contrail cirrus.

Reducing engine soot number emissions leads to lower initial ice crystal numbers and environmentally beneficial changes in the properties, life cycle and radiative forcing of contrail cirrus. Fewer ice crystals reduce the optical thickness of the contrail cirrus due to the reduced number of soot particles. Decreased cloud cover due to contrail cirrus-induced clouds exerts a smaller climate impact.

Field research on the reduction of soot emissions through the use of alternative fuels with a lower proportion of cyclic hydrocarbons is now underway. The German Aerospace Center and NASA are conducting joint research flights to investigate the effect of different fuel blends on soot emissions and the associated formation of ice crystals.

The research is published in Nature Partner Journal Climate and Atmospheric Science.