What caused the end of the world in the book version and the movie version? are they different?

In the "Androids..." the apocalypse is cased by a world war, most probably nuclear in nature. In Blade Runner, they never really tell us what happened. It's dark and raining all the time. That's to be expected in a Ridley Scott film but still, we never find out. I always thought that it looked liked humans completely screwed up the environment. That would make a lot of sense in todays world.