On Sat, 14 Dec 2019 07:50:07 +0000
The Natural Philosopher  wrote:

> On 13/12/2019 22:25, Ahem A Rivet's Shot wrote:
> > On Fri, 13 Dec 2019 19:07:58 -0000 (UTC)
> > Martin Gregorie  wrote:
> >
> >> The effect was attributed to the lack of jet
> >> contrails, which normally lower the average temp by preventing sunlight
> >> from reaching the ground during the day and prevent it radiating into
> >> space at night. Here's a summary:
> >
> >  I find it very hard to believe that there's enough contrail
> > coverage to have that effect.
> >
>
> Oh, there is.

 Hmmm.

> Why didnt you say 'I can hardly believe there is enough CO2 to have that
> effect'?

 That seems to be a rather more complex question than "how much
difference does a reflective contrail make" which boils down to "how much
energy does it reflect into space". People have talked about deploying
reflectors of some kind to control climate and they've always seemed to
need to be unreasonably large, it's surprising to me if the combined
contrails makes a large enough reflector to have such an effect. Many true
things are surprising though, so it may well be the case.

 The thought that occurs to me is that if normal US domestic air
traffic really does reduce the temperature over the US by two degrees (by
reflecting sunlight of contrails or any other mechanism) then we have the
solution to global warming without even considering the causes. All we have
to do is arrange sufficient contrails to dial in the temperature we want
with fast (three days made it show clearly) response.

 Of course reasoning from a single data point and an untested theory
is a good way to go very wrong, but I would find it hilarious if it were
proven and the next move was to encourage widespread air travel in order to
improve the climate.

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