Statistics of potential radiative forcing of persistent contrails

Abstract

Contrails affect climate if they are persistent, that is, if they are located in an ice-supersaturated region (ISSR). They do this by reflecting sunlight back to space (cooling) and by blocking thermal radiation from the Earth surface and lower atmosphere (warming). During night, there is always net warming since sunlight and thus it’s possible reflection is absent. In most (daytime) cases there is substantial cancellation of the warming and cooling effects, but occasionally (in particular during night) the long-wave warming effect dominates such that the respective contrail has a particularly strong contribution to climate warming. This is a Big Hit, and such contrails should be avoided already in the flight planning phase. Such an avoidance strategy needs of course a reliable prediction of the conditions under which contrails actually are that strong climate warmers. The topic of this presentation is how situations with strong warming contrails can be characterised and whether and how reliably it is possible to predict them.