collapse of the old society

It varies depending on location. A more accurate name would be global weirding. Some places will get wetter, some drier, some areas will get much warmer, some will have more extreme cold events.

We might see a shift in air currents making the Sahara desert move back to being a grassland and Europe could lose much of its rainfall. Established agriculture will likely have a hard time adjusting to the new climate and could cause global food scarcity.