While I understand the idea (there are nuances) I wonder if we treat things fairly. I have never measured gravity directly. I can notice effects which I know are attributed to gravity (things falling), but then again I can see effects attributed to human CO2 emissions (weather getting warmer and crazier).

The scientific concept of gravity (as I remember it from high school) involves two bodies and the distance between them. I can't measure that at all, so someone could claim gravity does not exist, but things fall because of some other reason.

What I think it's more important is the system's complexity. Describing gravity as "two objects, bigger one attracts smaller one" is simple. Climate system is very complex and even if you describe "CO2 (a transparent and 0.04% part of the atmosphere) causes a warming of couple of degrees" sounds harder to picture.

Yes, the complexity of verifying/checking is a major factor of that "nuance".

In the end, Newtonian gravity's complexity can be boiled down to a few formulas, and those describe the phenomenon (and are quite simple). Something like climate change causes, progress, rate, and so on, even with many basic assumptions taken for granted, is still a huge and multivariate issue.

One can see that "weather's getting warmer", but it could be a process repeating every N centuries or millenial, and we're just at that point, others might argue the effects are not as dire as argued, or the rate not as fast (e.g. many public climate doomsday predictions have failed to arrive when the dates came and went). Or one might totally disagree about the proposed solutions (or with who and how gets to implement and impose those solutions, another can of worms).

That's more like string theory level nuance (which theoritical physicists still debate variants off, and some hardcore scientists even believe is speculative crap, and which in any case is nowhere near settled), than Newtonian gravity level nuance.