We need to start to understand as humankind that we're a pest to other life on this planet, be it animals, plants, naval lifeforms or anything else, us included (maybe except tardigrades, extremophiles and deep-sea creatures).
We need to reduce our numbers, and sustain that. Or embrace Musk's ideas.
Population isn’t the problem, first world consumption and the expansion of the first world are. This isn’t an abstract problem where people in developing countries need to have less children. This is a problem where we need to personally reduce our carbon footprints.