What you're talking about re: the cities and temperature is called the "heat island effect." And on that note, here's an article talking about how the heat island effect actually helps trees grow faster: https://www.citylab.com/environment/2012/04/urban-heat-island-upside-it-can-be-good-trees/1847/

And here's an article talking about how lots of tree planting can help mitigate climate change way more than probably most people think: https://www.theguardian.com/environment/2019/jul/04/planting-billions-trees-best-tackle-climate-crisis-scientists-canopy-emissions?fbclid=IwAR340BGlYKkQgorYk9AK7JFZ4qRYrbO9OGiLh5qbyRZ7BgAemT_UydmfZhQ

And here's a SciShow episode about how the change from Earth being a greenhouse planet to going through ice ages ~50 million years ago is thought to have happened due to one type of fern!

...so yeah, plants have a lot of power. :)

Basically, my philosophy that I got a bit into in a post a few weeks ago is: do I acknowledge that most of the problems are coming from big polluters like oil and gas? Yes. But that doesn't mean that I throw up my hands and fiddle while Rome burns, so to speak. People tend to get nihilistic when they realize that all their lifestyle changes are essentially a drop in the big bucket compared to, say, one oil company, and think, "why bother?" I see personal changes as a) not making the problem any worse; b) giving me a sense of hope, which is super important; c) making my local habitat a bit nicer; and d) rekindling that connection to the rest of the world that we humans tend to lose living in isolation in human-built city habitats with various natural processes done out of sight, out of mind. Basically, we're not going to change on a societal level if we don't change on an individual level, imho.

NTM, societally speaking, you can have a lot more effect on the local society - say, your city or your state or whatever - and then all these cities adopting changes like, green roofs or renewable electricity or waste management, etc. - can have a domino effect.

That being said, of course, money-making interests will often try to dilute those changes, as seen in Denver voters passing a green roofs initiative and then city council watering it down to be pretty much pointless after the fact. They CLAIMED that it was because not all structures can support green roofs, but there were stipulations for exactly that in the bill (like, you can do solar panels instead, and so on). Basically Denver/Colorado governments are in the pockets of developers (because of the price of real estate here) and oil and gas (because fracking). So even in local politics, we've been fighting against lots of monied interests, and the brown cloud of pollution has gotten worse. Some days our pollution is worse than Beijing.

But again, do I sign the petitions and call my reps and even collect signatures to get things on the ballot? Yes. But do I also plant trees and compost and all the other things? You betcha. I see things as being multifaceted. Would I like our government to be different than the system we have now, absolutely ...but in the meantime, I have to live in the system we have, so I work on problems from as many angles as I can.

And for the record, trees in pots:

...that's my three year old elm tree grown from seed on my balcony, tyvm. ;)