The more these discussions progress, the more I wonder if there is really only one solution. We need less people. Trying to convince 8 billion people to do something like never eat meat or fish seems like an impossible goal. We need to raise the standard of living in countries that reproduction rates > 2. We could also remove tax breaks for kids after the second in developed countries to mitigate the incentives for extra children. Maybe if we only had 4 billion people, we might be able to have everything be sustainable. Such a hard problem to solve.