well, goggle 9/11 and climate to get a slew of articles taking every possible position... but the fact remains, for three days there was a ban on non military flight over the USA. Jets leave contrails... no jets no contrails. A direct & immediate change in weather was noted. It helped reveal a small facet of human influence on the atmosphere.

It is an undisputed fact that industry pollutes... as in sends up tons and tons of soot ( aka particulates) and just as much assorted chemicals into the atmosphere. Some of these chemicals act as catalysts to destroy the protective ozone layer and others act to trap heat within the atmosphere, known as the "greenhouse effect", while others create "acid rain" or just act any other toxic chemical when introduced into an organism.

If you question these facts, then go the US EPA website and look up any of the thousands of Title IV and V permits that have been issued since 1997 to get a clue. They just happen to list the various chemicals and the amount that a company is allowed by law to emit from their plants. And that's just in the USA. I know this for a fact because I used to work on these permits in New York. Now I work on water pollution permits. SSDD

PS... as a geeky footnote... the very first air pollutant was free oxygen, O2, that is the end product of photosynthesis. yes it took time... but it DID change the original reducing environment of this plantet into an oxidizing one... which is the prime reason why multicelluar organisms could make a real go of it. The end result is what we have today.