On Thu, 14 Jan 2021 10:26:59 +0000, Ahem A Rivet's Shot wrote:

> On Thu, 14 Jan 2021 05:48:16 +0000 The Natural Philosopher
>  wrote:
>
>> (iii) Its down to high flying aircraft contrails, so we should just
>> stop flying.
>>
>> Of these the only currently  *testable* one is (iii) and when air
>> transport did shut down post 911 there were in fact colder nights in
>> the USA. And post Covid 19 shutdown there has been a rather cold
>> northern hemisphere winter.
>
>  I've seen comments that during the 911 flight shutdown the average
> temperature over the US rose a little. I have no reason to doubt either
> that observation or yours, it is just an indication of how difficult it
> is to test even that hypothesis - let alone ones like "It's a mix of i
> and ii proportions unknown". Personally I don't believe anything that
> ascribes a single cause to a complex phenomenon because I ain't seen one
> yet.

Its quite possible that both are true and that both are due to the same
cause - the absence of jet transport contrails over the continental USA:

- daytime temperature rose and the skies looked clearer because there
  were no contrails reflecting sunlight back into space. NOAA reckon that
  average daytime temperatures rose by 3 degrees Fahrenheit during the air
  travel shutdown and many American glider pilots commented, in
  rec.aviation.soaring, on how much clearer the air had been.

- I assume the same happened at night, but it would work in reverse, with
  the lack of contrails at night allowing the ground to cool more because
  they weren't there to prevent heat from radiating out through the
  atmosphere. I don't remember seeing any comment about this though, or
  seeing any estimate of what the temperature drop was.


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Martin    | martin at
Gregorie  | gregorie dot org

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