i understand that probably doesn't fit OP's lifestyle, and i'm not suggesting they move to an apartment. but i think it's important to acknowledge that dense urban living can have significant environmental benefits over the sort of self-sufficient, off-grid, rural lifestyle that's typically regarded as being more environmentally friendly. cities, and specifically apartments, are very efficient.
Although high density can be more energy efficient, it’s not the only metric to consider. Apartment dwellers are completely dependent on importing resources, while rural people at least have a chance at breaking the dependency.
At best, you've proved that a planet composed entirely of cities is unsustainable. I hope nobody wants that, but sadly some people do.
If you’re talking about high density in a concrete city, then cooling is a problem.