In his last book, “Billions and Billions,” published in 1997, Carl Sagan wrote: “There is a well-documented worldwide correlation between poverty and high birthrates … exponential population growth slows down or stops when grinding poverty disappears. This is called demographic transition.” More recently, John Ibbitson and Darrell Bricker wrote in their book, “Empty Planet”:

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The great defining event of the twenty-first century — one of the great defining events in human history — will occur in three decades, give or take when the global population starts to decline. Once that decline begins, it will never end. We do not face the challenge of a population bomb but of a population bust — a relentless, generation-after-generation culling of the human herd. Nothing like this has ever happened before.

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Now a new study published in The Lancet with a paragraph-long title, Fertility, mortality, migration, and population scenarios for 195 countries and territories from 2017 to 2100: a forecasting analysis for the Global Burden of Disease Study makes the point again:

Our findings suggest that continued trends in female educational attainment and access to contraception will hasten declines in fertility and slow population growth. A sustained TFR [total fertility rate] lower than the replacement level in many countries, including China and India, would have economic, social, environmental, and geopolitical consequences. Policy options to adapt to continued low fertility, while sustaining and enhancing female reproductive health, will be crucial in the years to come.

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