>>212709230 (OP)500 million isn't nearly good enough (the Georgia Guidestones had the right idea). What's needed is to get the population not only back down to the pre-industrial norm of 200M, but WELL BELOW, somewhere on the order of 50-150M, and then KEEP IT THERE IN perpetuity, so that those living can both enjoy greater living space, lower intra-species competition, and also continue to burn fossil fuels at a much lower rate. The trick is to manage the population pyramid downward during this painful process, to minimize the suck for what is necessary. Elder care is just simply going to have to collapse, or at least become very difficult. Immigration is NOT the answer, and never has been. Fewer human beings is the answer, but no one wants to seriously think about that because it runs contrary to human instincts. Human instincts are ill-equipped to manage the problem. Worse, the poor Africans breed more rapaciously because they need multiple children simply to fetch water from the well and perform basic household tasks.