Because China wants to rule the world. That includes roughly being seen as a great bastion of awesomeness.

The huge solar rollout is very much because China thinks it might end up in a war, and they are currently very vulnerable to a blockade for energy resources, and grid scale solar is unblockadable for like 20 years. You can bomb it, but that's a hard mission.

If what I believe is correct, there would also be evidence of China creating unblockadable food transport lines and relationships.

Global Warming is well understood all over the world. China doesn't want the world to suck right before they finally undo their Century of Humiliation and retake their "rightful" place as mega empire that exports culture and tech and power. They want to be the super power ruling over an awesome world, not ruling over ashes.

I've heard arguments that China has fairly limited "Soft power", and they really want to fix that, which takes actions that at least look altruistic and win-win.

With the US self-defeating, China is in a great place to be the leader of a stable world, and even be a counterweight to an abusive USA.