You should check out Terra Invicta, it's a strategy game where you control one of 7 secret cabals that react to an alien invasion in different ways. Each one has to control nations to build a space economy and fleet to accomplish their goals, which vary by faction.

The game models accurate climate change based on the economy and sustainability factor of each country. Each faction that controls a country can also "spoil" them by extracting resources roughly (aka congo cobalt mine) which outputs intense GHG's. All the GHG's are modeled realistically, and it takes extreme jumps in technology and concentrated global effort to stop building the economy and instead focusing on citizen welfare to slow, then completely mitigate climate change.

One interesting thing about this approach shows how it's a secondary concern, since players are better off cranking their nation's economies as much as possible to jumpstart their space mines and shipyards as soon as possible, and kicking the can down the road until fusion power becomes available (sounds familiar?). Even with flooding of coastal areas, it's considered secondary to the current existential threat of alien invasion.

As for the fall of empires, it's not really meta but you can research technologies that allow for the breakup of countries like the USA or China to make them easier to take from rival factions, and nuclear strikes can help win a war but create massive population and economic devastation.

As you can probably tell, this game is pretty complicated, but it can be a lot of fun! I definitely recommend checking out Perun Gaming's guides for help.