For all the attention that global warming gets as an environmental hazard, there lurks one far greater. War.
Humans are getting good at playing the long game. We’re managing fisheries, curating wilderness, creating fantastic supply chains that extract fantastic yields from good cropland and deliver it to people. A substantial war would change all of that. If the short-term becomes more important than the long term, careful conservation and eco-friendly practices will be discarded by necessity. Without access to modern clean technologies, people will be forced to turn to dirtier and unsustainable ways of getting by. What would you do if no food arrived at the grocery store, and you had no access to electric power?
A nuclear exchange would be worse, and is far from improbable.
The human invention of technology has graced us with many gifts; we must use our powers well, for our own sake.