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| Condensation train of an Airbus A340 |
The contrails, these contrails resulting from the airliners passing over our heads create certain climatic disturbances and in addition to anthropogenic forcings promoting greenhouse.
According to a recent study, with the intensification of air traffic, contrails should be multiplied by three by 2050. Their impact on global warming, already currently significant and yet underestimated, could then be greatly increased.
What is a contrail?
Cirrus homogeneous, this Latin name perhaps says nothing to you and yet we observe every day if we look up at the sky: it is simply artificial clouds that are formed as a result of passing an airplane because of the steam emitted by their engines when flying at high altitude. This phenomenon is more commonly called contrail, contraction of the English words " condensation " and " trail ".
However, most observers will certainly have noticed that contrails do not form systematically this phenomenon requires that several conditions - including temperature, humidity, and altitude - be met.
Contrails: an impact on the climate?
A recent study published in the journal Atmospheric Chemistry and Physics believes that these contrails are not without effect on the climate and generate a radiative forcing that contributes to global warming.
The results of this study do not stop at this information, already known and yet underestimated; the two German researchers at its origin estimate that these disturbances should be multiplied by three by 2050 due to the increasing increase in global air traffic (which doubles every 15 years), as well as the evolution of airlines whose tendency is to move them to significantly higher altitudes.
However, if one often points the planes with a finger because of their important emissions of greenhouse gases, in particular, CO 2 and NO x , it is finally the contrails that would play a more determining role on the climate, despite their low persistence relative to CO 2 emissions.
Made up of ice crystals that form when the water vapor mixes with cold air outside (at least - 39 ° C), the contrails tend to form large streaks turning into cirrus, which go reflect the sunlight during the day and therefore cool the air masses with their albedo (reflecting a surface). Only this is the contrails will eventually oppose the cooling of the soil and air masses by trapping heat.
Unfortunately, their nocturnal effect is far more dominant than their daytime effect. Thus, the IPCC estimates that air transport is responsible for 4.9% of total anthropogenic radiative forcing. The contrails and the resulting cirrus are responsible for most of the greenhouse effect induced by air traffic, far ahead of CO 2 emissions.
The air transport sector will, therefore, have to find a convincing solution to reduce the radiative forcing induced by contrails, perhaps by modifying certain routes to avoid saturated areas, planning flights at lower altitudes, or by attempting to reduce the density of these trails.
Finally, the arrival of hybrid and electric aircraft in the aeronautics sector may have the effect of reducing the number of daily contrails! Only the future will tell us.
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