Much of the world is on track for zero population growth. Birth rates in many countries are at the replacement rate of 2.1 children per average couple, or lower.
The change, in my opinion, has come about because (1) knowledge and availability of birth control are widely available, (2) women are emancipated and have control over their bodies and (3) people are raised far enough out of absolute poverty that they think it is better to have a small number of prosperous, well-educated children than to have many children.
I think that, in the long run, Muslims and Hindus will be as willing to practice contraception as Catholics have proved to be.
One is that there will be relatively fewer adults in the prime working years compared to elderly retirees (such as myself).
The American solution to this has been immigration, but this generates its own problems. The United States has limited resources, including water supply, and can’t absorb large-scale immigration indefinitely.
The projections and forecasts by the United Nations and others are possibilities, not certainties. And even if the predictions and forecasts are correct, the world’s population will become larger than it is now before it levels off. But, based on past experience, I don’t see this as cause for despair. There are grounds for hope.
The Great Contraction: Experts Predict Global Population Will Plateau by the staff of Der Spiegel
World population may actually start declining, not exploding by Jeff Wise for Slate.
Human population growth and the demographic transition by John Bongaarts for Transactions of the Royal Society of the Biological Sciences.