I feel like nuclear energy is getting overlooked. Modern advances allow for re-enriching waste material, so it can be reintroduced into the reaction. With careful construction and planning, it's the safest, greenest, most efficient energy source we have. And it requires no new research. The tech already exists. Widespread standardization and adoption could give us the breathing room necessary to halt any more permanent warming without sacrificing living standards for most of the world. Hell, if we can force developed nations to foot the bill, it could even raise living standards in underdeveloped and exploited nations.