And it’s not as if the world has been standing still over the last decades, huge progress has been made and many technologies are at the borderline of being economical or cheaper than the alternatives, and are continually falling in price. Once we push the boulder over the crest of the hill it will roll down unaided. The economy can change much quicker than we think.
I agree that many technologies for replacing fossil usage have now achieved or are close to economic superiority, and that change can come very rapidly with economic superiority. But I also think that reaching this point has taken too long and now we will need active measures as well as emissions cuts.
So, due to these different marginal costs, there's no way even completely practical, economical solar can stop fossil fuel usage quickly without active regulator intervention.
If you do something fairly extreme for curtailment, like a tax on fuel that motorists really notice, the other party will get voted in and they'll undo it. Now you've got kicked out of office, with no environmental benefit to show for it.
And if you go further with something like a ban on pet dogs or ban on meat-eating? Same thing but faster and with more certainty.
