We don't need any major tech breakthroughs, what we need is to put in actual effort, money, and political capital into trying to solve the biggest long term threat facing our species. The solution has been around for at least forty years in the form of the nuclear lightbulb reactor [1].
This research was completed by the United Aircraft Corporation in the late 60's and early 70's before it was canceled by Nixon along with the Mars program. It was under a NASA contract for space exploration so the literature was written in the context of the arms race but it is even more compelling as a terrestrial reactor as it uses a tiny amount of fuel (tens of kilos instead of tens of tonnes) and actively keeps that fuel at supercritical so if power is lost the entire thing fizzles out. This is a fast neutron design with an extremely high neutron cross section, far beyond that of any other reactor, easily allowing you to feed nuclear waste into it and very efficiently transmute much of it into fuel or more manageable waste that is then separated out by centrifuges (which are already in the design to separate usable UF6 from the neon exhaust). UAC was set to win a contract to test the reactor with nuclear fuel when Nixon pulled the plug. They even had a design mapped out for a slow neutron reactor that would have made it economically viable in the 70s.
All of the technological breakthroughs in computation, material science, and nuclear engineering needed to make this happen at an industrial scale have been discovered since the project was canceled. If it weren't for all the anti-nuclear hysteria, we might have actually had someone willing to take the risk to bring the nuclear lightbulb reactor to market. Sadly, almost all of the scientists and engineers that worked on this design have passed on so the institutional knowledge is gone and our best opportunity to head off climate change remains bogged down by pointless arguments over thorium and molten salt reactors.