It was more the "chemical H2O" that caught my eye.
On the point of the effect of aerosols from jet engines on temperature, other than that post 9/11 Nature article I can't find anything other than discussions that in principle since clouds affect temperature, so too would contrails. There is an acceptance that radiation will also be scattered back out of the atmosphere. So as yet no quantification or even destination of positive or negative impact on temperature.
The Nature article itself refers to a net temperature increase due to the absence of air traffic, which is the opposite of the suggested effect in the subsequent hand wringing debate.
This would also appear to be a local effect, not a global effect, very small at most, and the actual contribution of the absence of contrails not quanfiable. Would be interesting to read the whole thing, though.
