Some interesting responses and links, however it still looks to me like there is a vast vast amount that science and certainly us don’t know about the climate and how it gets influenced both naturally and by us as a species.
There was some interesting info provided in one of the links that states that CO2 lasts in the atmosphere for years while H2O only lasts for a mater of days which I found very interesting. This could be a very significant difference between hydrogen and carbon based fuel exhaust emissions which could possibly warrant further scientific study.
At the risk of appearing stupid, I think it’s very easy to overly simplify things by saying that on a cloudy day it’s warmer and vice versa, however that’s not always the case. On a cloudy day during the day it blocks some sunlight and keeps the earths surface and therefore local atmosphere cooler, however at night a cloud layer insulates and keeps the air warmer.
Thinking completely outside the box, maybe rather than ban flying on certain days maybe it would be better to ban night flights when contrails could keep the atmosphere warm.
I hope that most of us on this forum want to continue having the benefits of flying, and aviation is a unique form of transport in the way that we go up into the upper atmosphere rather that stay on the earths surface.
I just hope that science will find a way for this to be turned into an advantage as opposed to the perceived negative that it is at the moment in certain circles.