On one hand many countries will invest in heavy industry, manufacturing, and fall back to fossil fuels.
On the other hand, economy overall should slow down and consumption of non-essential goods and services will drop.
I’m not expecting any definite answers or numbers, of course, just some food for thought.
We already have a model of this with Israel’s genocide in Gaza wracking up a climate footprint bigger than entire countries. Scale that up to a world war and… Yeah, not fun.