I am back from a 2 days workshop in Zurich where the whole city apears so clean and organised that it kind of make wanted to stay but thought I might get borred after a couple of month, so got back happy in the french capital without forgetting to grab some swiss chocolate before take off. I was invited to join this workshop which focus on the airplane emission to show what would be this impact of airplane transport on temperature in the future as the air transport is planned to increase intensively. It is also a great interest for modellers like me to know what is actually coming out from the exhaust of an airplane as it is a crucial input for my model. As you might guess it is not an easy task. As the workshop was on his final lap, I had a striking conversation with a engineer hired by a famous plane manufacturer. In the presentation, I just gave, I extented my modelling results up to 2100 which I was pretty proud of. Unfortunately, the engineer was not and the reason was quite interesting or depressing dependind on which angle you were looking at it. As he had quite an experience in world of air transport, he simply told me, there was no way , we could know if the conception of an airplane would carry on in 2100, the way we are experiencing it today. In other words, nobody could actually forecast, with acceptable accuracy, the airplane emissions in the future (after 2050) and he added: the change from aircraft propeller to the jet engine technology was done only over a 20 year period... That was quite a conclusion from this workshop!