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Re:Climate change and the 1991-2020 U.S. Climate Normals by Diederich on Monday April 26, 2021 @02:54PM (#26946480)
Only slightly educated guess forthcoming.

Air pollution was pretty bad in the United States from the 1950s through the late 1980s, and we know that https://en.wikipedia.org/wiki/Global_dimming has kept temperatures down a bit.

So basically from the early 1970s through the 1990s in the United States, the amount of 'global dimming' type air pollution decreased tremendously, because of a number of factors, including all sorts of clean air mandates and regulation.

Re:Climate change and the 1991-2020 U.S. Climate Normals by kossTKR on Monday April 26, 2021 @03:10PM (#26946666)
The dimming factor seems a bit frightening.

I don't know how sound the theory is, but i remember listening to the climate podcast Radio Ecoshock where a scientist talked about aerosols in general and that there could be a negative feedback loop that would disappear if we stop polluting heavily, ironically then raising temperatures significantly - this could mean that an extremely agressive decrease towards 2030 could increase temperature weirdly enough.

The effect was seen over the US after 9/11 as far as i remember.

A damned if you do and don't situation.

Re:Climate change and the 1991-2020 U.S. Climate Normals by pedrocr on Monday April 26, 2021 @03:41PM (#26947056)
> The effect was seen over the US after 9/11 as far as i remember.

There was a study that claimed that but there's a second study that claims general cloud cover was a confounding factor not controlled for that explains the actual result:

https://en.wikipedia.org/wiki/Global_dimming#Contrails_and_c...

Even with a full set of airplanes in the air contrails are a tiny minority of the cloud cover. Seems pretty hard for them to have any visible impact. Aerosols in general are another matter all together. Those are all over the atmosphere and it wouldn't be surprising if they had a large effect as they accumulate.

Re:Climate change and the 1991-2020 U.S. Climate Normals by kobieyc on Monday April 26, 2021 @04:11PM (#26947441)
Related to cloud cover: one of the biggest uncertainties in climate models is how to cater for the albedo effect also known as cloud feedback. It goes something like this:

1) The most potent greenhouse gas is water vapor (not CO2) 2) Increased temperatures result in more water vapor (simple evaporation) 3) Water vapor forms clouds 4) Clouds are white and reflect incoming solar radiation

A lot of models have to make big assumptions about the strength of this negative feedback loop, and the assumptions have a big impact on the output of the models.

https://en.wikipedia.org/wiki/Cloud_feedback

Re:Climate change and the 1991-2020 U.S. Climate Normals by Retric on Monday April 26, 2021 @06:44PM (#26949257)
Conversely, further increased evaporation > even more water vapor > increased precipitation > fewer clouds.

Also, clouds reflect sunlight > less warming, but clouds reflect IR > less cooling.

It’s a really complex interaction that doesn’t have a clear global maximum as each region has a slightly different impact and they all interact. Atmosphere dust is one of the biggest drivers here and dust alone involves a lot of non linear feedback loops.

Re:Climate change and the 1991-2020 U.S. Climate Normals by mcswell on Monday April 26, 2021 @08:20PM (#26950071)
"further increased evaporation > even more water vapor > increased precipitation > fewer clouds." No. You can't get fewer clouds from more water vapor, that's not how equilibria work.
Re:Climate change and the 1991-2020 U.S. Climate Normals by Retric on Tuesday April 27, 2021 @08:19AM (#26954890)
Clouds are dependent upon the particulate matter in the air, which is reduced by precipitation. You still get cloud formation without that, but the air ends up very supersaturated.

https://en.wikipedia.org/wiki/Cloud_condensation_nuclei

Re:Climate change and the 1991-2020 U.S. Climate Normals by kossTKR on Monday April 26, 2021 @03:51PM (#26947181)
Thanks for the clarification. Always seemed a bit too quick and neat a causation.

But as you say the bigger picture is still worrying - and i am not sure that disregarding cloud formation there isn't still certain aerosols hanging around changing things for the worse after heavy air traffic - it's hard to gauge from the Abstracts of papers i just skimmed, but something seems to be happening : https://link.springer.com/article/10.1023/A:1006600107117 https://www.researchgate.net/publication/279155481_Impact_of...

Re:Climate change and the 1991-2020 U.S. Climate Normals by ip26 on Monday April 26, 2021 @05:40PM (#26948545)
Well, we can always spray sulphur aerosols in the stratosphere without all the CO2 and acid rain.