Comment by jmcqk6

Not the person you're replying to, but I think I can explain it this way:

The quality of life of a human being is directly related to the amount of free energy (i.e. thermodynamic free energy, not free as in no cost) they have access to. Life must be able to generate more energy than it needs, even tiny bacteria. As humans developed, we found more ways to access and utilize free energy.

There is a phrase: Energy return on investment (or EROI). You can map the development of humanity pretty cleanly to an increasing EROI over the entire course of our history.

Fossil Carbon allowed us to explode our EROI and gave us access to never before seen amounts of free energy. Unless we find ways to maintain that EROI, our quality of life will necessarily diminish.

Obviously we need to cut our use of fossil carbon. And if we don't, we're simply going to run out, and then we'll be stuck anyway. But we also don't have anything with a comparable EROI to replace it with.

This is the root problem we're facing. If we had working fusion, it would be a whole lot easier to decarbonize.