By strict rationing of key energy and consumer goods until we can walk back the Earth's population to a sustainable size. If we reduced the fertility rate by half a child to 2 instead of 2.5, we would reduce the world population by 1 billion by 2050.

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https://populationmatters.org/solutions

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https://medium.com/politically-speaking/why-is-a-larger-human-population-better-7ef66eb21511