The vapour trails left by planes have a more damaging effect on the climate than all the carbon dioxide ever emitted from their engines, according to the findings of a new study.
Contrails linger in the sky as ice clouds (cirrus clouds) that trap heat in the Earth's atmosphere, an unaccounted for source of non-CO2 warming from air travel.
And researchers from the Institute of Atmospheric Physics in Germany say the problem is set to triple by 2050.
Already flying is responsible for five per cent of global warming with the industry set to dramatically expand in the coming decades and little political appetite to stymie this growth.
"It is important to recognise the significant impact of non-CO2 emissions, such as contrail cirrus, on climate and to take those effects into consideration," said lead author Lisa Bock from the German Aerospace Center (DLR) at the Institute of Atmospheric Physics.
Currently the Corsica agreement, which is the UN's scheme to offset air traffic carbon emissions from 2020, ignores the non-CO2 climate impacts of aviation.
However, the new study will raise alarm over the climate impact of contrails. Researchers say the radiative forces of contrails will increase relatively more than the rise in CO2 because planes of the future will be more fuel efficient.
Overall air traffic is set to be four times larger in 2050 compared to 2006 levels but planes are generally flying slightly higher, which favours the formation of contrails in the tropics.
Areas over North America and Europe will be most affected as this is where most traffic is, according to the study published in the European Geosciences Union (EGU) journal Atmospheric Chemistry and Physics.
Dr Bock said: "There are still some uncertainties regarding the overall climate impact of contrail cirrus and in particular their impact on surface temperatures because contrail cirrus themselves and their effects on the surface are ongoing topics of research. But it's clear they warm the atmosphere."
More efficient aircraft would reduce the number of soot particles emitted by engines, which could in turn reduce the climate impact of contrail cirrus.
However, researchers say larger reductions than the projected 50 per cent decrease in soot number emissions are needed.
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