At some stage, a consensus must build for stopping our destruction of the climate. (Well perhaps it won't, but in that case we're doomed, so there's little point in evaluating that path).
At that point, some countries (presumably rich ones) will have cleaned their own houses emissions-wise and be signed up to assist poorer nations.
It will then become unacceptable to them that their efforts are in vain and at risk, because other countries are free riding and doing nothing, and continuing to pump emissions into the atmosphere.
Their mindset will move from pride at their own achievements to anger and frustration at others.
Soon after that will come enforcement. After all, it cannot be unreasonable to stop other countries from destroying the environment that we all share - even if those countries have to be destroyed to save the planet.