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.
Speed up by far. All the focus will be on producing enough stuff to replace whatever the enemy blows up. Any invention in the renewable department will only come as a result of having used all available fuel already.
The world population still increased during the previous world wars so unless we have a major nuclear exchange that probably won’t change. If we do have a major nuclear war global warming is suddenly not a big deal anyway.
I was going to say, it really depends on just how hard we go on the “let’s kill everyone” vibe.
Also a lot less death more injuries than previous wars. With the same amount or more of environmental destruction.