You would find economic ways to disable these companies from operating. You mustn’t buy a whole company to do this. Maybe you buy a key piece of real estate they need and tie them up in court for years. Maybe you find key employees and hire them away and pay them to garden at the Spheres in Seattle. Maybe you convince a port to no longer allow the transfer of coal through there using economic coercion or donations to city hall. Or you acquire the water rights near a coal plant so it can’t run its cooling operations, forcing early retirement.

Lots of ways to skin a cat. Find the linchpin and apply as much force necessary with as little cash possible. One can be efficient and expedient simultaneously. I agree you have to do the math to pick the opportunities that allow for offsetting/retiring as much CO2 per dollar spent as possible.

I’ve put together notes along these lines if someone with deep pockets is interested. Economic warfare is the most exciting exertion of force imho.