Global air traffic is expected to quadruple by 2050 compared to 2006. The predicted strong increase in air traffic volume could triple the climate impact of contrail cirrus, which was the result of a study published on 27 June 2019 by the DLR Institute of Atmospheric Physics.
Under humid and cold conditions, contrails and contrail cirrus that develop from them can remain in the sky for many hours. Their effects on the global climate system have not yet been recorded in emissions trading agreements designed to limit aircraft emissions. Contrail cirrus contribute to the warming of the atmosphere to a similar extent as the total accumulated CO2 emissions from aircraft since the beginning of aviation.
Emitted CO2 has a global and decade-long effect on the climate, while contrail circles have a regional and hourly effect. In North America and Europe - the busiest air traffic regions in the world - the effects of contrail cirrus on the climate will continue to be by far the greatest, but they will also increase significantly in Asia.
The number and size of the ice crystals at the time of contrail formation depends on the soot particle emissions from the aircraft engines. When the emissions are reduced, the number of ice crystals in newly formed contrails decreases, which limits the lifespan and climate effect of these anthropogenic, high-altitude clouds. Reducing soot emissions is thus an important step towards reducing the climate impact, but it is probably not enough.
Radiative forcing due to the formation of contrails for present-day climate conditions and (a) present-day air traffic volume, and (b) for air traffic volume expected for the year 2050. Panels on the right hand side show the radiative forcing for climate conditions expected for 2050 and (c) air traffic volume for the year 2050, and (d) air traffic volume for the year 2050 assuming an increase in fuel efficiency and a 50% decrease in soot emissions. The numbers in the boxes show the global mean radiative forcing for each simulation. (Grafik: ©DLR)