Collective action is essential but the way forward is through smaller efforts as pilot projects and to prove the market.
Setting a good example doesn't inevitably result in everyone following along, but a proven solution is a whole lot easier to sell than a proposal that's never been tried at scale.
I'd go further and say there could easily be a set of outcomes where it's a big first mover advantage for anyone who develops the approach that works in any of the many niches needed to move forward. And for the first nation that systematically enables that kind of scaled climate focused development - they'll get huge payback as the effects get worse and lagging nations pony up the money to mitigate effects and go to leading nations and companies looking for solutions with any sort of track record.
Setting a good example doesn't inevitably result in everyone following along, but a proven solution is a whole lot easier to sell than a proposal that's never been tried at scale.