No idea how we do that. Tearing down capitalism without a clear plan could kill almost as many as climate change itself (We're starting to wake up to just how fragile our modern 'life support system' of global supply chains is - we really don't want to find out how it handles massive revolutions or widespread war!)
But it's pretty clear that for every child not born (especially in the most wealthy and wasteful parts of the world), that's a whole lot of energy not used, miles not travelled, and meat not eaten.
And if if you expect the next century to be really grim as we feel the full force of uncontrolled climate change, then do you really want to bring kids into the world?