You could cull three billion people of the lowest emitters and it would have as much of an effect as halving the CO2 emissions of the top 1% of emitters.[1] And considering that to avoid the worst of the climate crisis we need action immediately or as close to it as possible, waiting for people to die away will not help us. If the entire planet stopped having babies today we would wait 65 years to get to half the current population, and half the emissions.
At best, and I would argue even that is a stretch, population control is one small part of a long term strategy. But it is by no means a solution, so throwing it out there every time people talk about sustainability does nothing but derail the conversation.
What we really need is to to make consumption as sustainable as possible and reduce it where possible, especially for the top consumers. That is not only more feasible in the short term, it is probably more ethical as well.
(Pasted this comment from [2])
[1] https://www.oxfam.org/en/press-releases/carbon-emissions-ric...
