Consider: it seems that we should be able to support a technological civilization of billions of people on renewable energy alone. That means literally on a fraction of the sunlight that Earth captures. Now, Sun isn't focusing on Earth, it's an omnidirectional emitter. Which means there's some 74 000 times more energy than Earth is receiving from the Sun available just in Earth's orbital band alone.
Fortunately, space-related energy problems seem like they'll be solving themselves, in lock step with increased space capabilities.
There's no way we're going to rocket launch billions to Mars, and there isn't another planet worth living on without unreasonable amounts of energy for Terraforming. But we are capable of rebuilding the atoms of Earth into much larger living environments - there are so many atoms it wouldn't mean destroying the Earth to do it. A Space Elevator doesn't need diamond nanowire, it could be built with enough steel chain. An orbital ring around the Equator would be enormous and would take approximately nothing of the Earth's matter to construct.
Isaac Arthur's YouTube channel is full of speculation and plans for all kinds of possible or nearly-possible futures, as well as more distant dreams. e.g. the playlists:
- "The future of Energy, Industry and Agriculture" - https://www.youtube.com/watch?v=ChTJHEdf6yM&list=PLIIOUpOge0...
- "Earth v2.0" - https://www.youtube.com/watch?v=i6mRjsxQQJE&list=PLIIOUpOge0...
- "Outward Bound" - near-Earth space exploration and living - https://www.youtube.com/watch?v=kmFOBoy2MZ8&list=PLIIOUpOge0...
- "Visions of Earth" - arcologies, megacities, ecumenopolises, geoengineering, weather control - https://www.youtube.com/watch?v=TqKQ94DtS54&list=PLIIOUpOge0...
And somewhere in there, megastructures such as Dyson Spheres, ringworlds, etc.
All the while the are almost endless resources and options how to solve these issues waiting in the solar system!
Its like hauling old people to the mountains to die because your village can't support them. We got over that & we should should get over our current terrestrial problems as well by moving on and expanding out of our cradle.