The difficult (and unbelievable) part of this hypothesis is how can they contain the nuclear explosions regionally and not allowing it to escalate out of hand towards a global thermonuclear war.

I think the obvious answer would be to egg on a situation where an exchange would be between a nuclear power and a non-nuclear power.

how can they contain the nuclear explosions regionally and not allowing it to escalate out of hand

the solution is clear, you just have to think (much) dumber and refocus from nuclear war as an excuse to the core of "exploding nukes will lower the global temperature"

Greenwashing Nuclear Weapons: USA paying countries to let them explode nukes in the desert to save the climate