Predicting the future is very hard (think butterfly effects, Lyapunov exponents and so on). It's also easy to extrapolate what would happen if the current situation continues unchanged, but very hard to predict what will happen in the near future in response to the current situation. People are already reacting to changes in politics and climate, thereby softening the blow, and maybe in some cases averting it.

I'm hoping Charles Stross knows this, and you should take his predictions as "this is what would happen if we did absolutely nothing about it".

If you're genuinely modeling complex systems with butterfly effects and uncertainty, you should sometimes be wrong in both directions. Sometimes things should be worse than predicted, sometimes better. If you're consistently wrong in one direction, that's not complexity - that's bias.