CONtrails

One day this winter I was coming out from work and as usual I was looking up to the sky, to see the amazing colours that at that time of the year sometimes the sky takes in the evening. This time though, instead of geting a redish sky “cel rogent-pluja o vent” I was stroken by a singularity of the sky “lloc geometric”: the beauty of the contrails mimiquing the facade of the building. In this point, and just before all this nonsense about the chemtrails became famouse due to the lack of rainfall, I asked myself:

How can contrails be modelled in the atmospheric/climate models?

Contrarily to what one could think, not all clouds produce a cooling effect on climate. The mechanism under the low clouds (e.g. cumuli) is that they reflect the shortwave radiation from the sun so that it does not reach the surface and is expelled again out of the earth system. On the other side, high clouds (e.g. cirrus) are more permeable to these shortwave radiation but they increase the ammount of shortwave (thermal) radiation that is retained in the earth system, hence having a heating effect.

Arrived to this point, as we know that the airplanes fly at the limit of the tropopause, we can say without doubt that the contrails are also high clouds that produce a net heating effect on climate. BTW this is a part that one should consider when discussing about emissions of the aviation sector, not only the CO2 emmissions but also these secondary effects that it is bringing.

So Francesc, how are they modelled? Ok Ok, wait, that is not an easy question. After an afternoon research on the internet I got to a nice presentation which

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