Estimate of the climate impact of cryoplanes

The climate impact of cryoplanes (i.e. hydrogen-powered aircraft) is estima ted in terms of radiative forcing (RF). We compare two scenarios: the conve ntional (i.e. kerosene-powered aircraft) scenario assumes a growth of the f leet until 2015 and a constant fleet thereafter. In the cryoplane scenario, the whole conventional fleet is instantaneously replaced by cryoplanes in 2015 and does not change thereafter. The resulting direct and indirect effe cts of aircraft emissions of H2O (direct RF and RF due to contrails) and NO x (RF due to O-3 production and CH4 destruction), as well as aviation-induc ed atmospheric CO2 are investigated for both scenarios. Whereas in case of conventional air traffic the components CO2, O-3, CH4 an d contrails cause a similar RF, in case of cryoplanes, contrails are by far the most climatic relevant component. In 2015, total RF due to the cryopla ne scenario is larger than total RF due to the conventional scenario. This changes with time and in 2100 the climate impact due to the cryoplane scena rio is smaller. Due to large uncertainties regarding the optical properties of cryoplane contrails, the RF of contrails, and the impact of aviation on 'natural' cirrus, our present knowledge is not sufficient to decide whethe r a substitution of the conventional fleet by a fleet of cryoplanes is of e nvironmental benefit. Further research is necessary in order to facilitate a more precise approach to this question. (C) 2001 Editions scientifiques e t medicales Elsevier SAS.