For every half degree of warming societies will see between a 10 and 20 percent increase in the likelihood of armed conflict. In climate science, nothing is simple, but the arithmetic is harrowing: a planet four degrees warmer would have perhaps twice as many wars as we do today. And likely more.
What accounts for the relationship between climate and conflict? Some of it comes down to agriculture and economics: when yields drop and productivity falls, societies can falter, and when droughts and heat waves hit, the shocks can be felt even more deeply, electrifying political fault lines and producing or exposing others no one knew to worry over.