There is a scenario. The climate has been buffering global warming, and as its ability to do that fails, the rate of temperature increase accelerates along with many extreme climate events. This rapid acceleration and series of catastrophes causes a combination of mass migrations along with unprecedented crop failures. First world countries are destabilized by sky high food prices and the mass influx of migrants, leading to a big uptick in wars and revolutions. Eventually mass starvation pushes us into wars for food that quickly spiral into mutual annihilation.