If you are a 57-year-old man from India, there are 6.3 million people like you on Earth.

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Demography “affects almost everything,” said William H. Frey, an American demographer and senior fellow at the Brookings Institution.

More young people will require more schools; a growing elderly population will necessitate an expanded safety net, and a young workforce to care for them; aging countries may need to reassess their immigration policies.

While on different timelines, each country is ultimately moving in the same direction — “toward longer lives and smaller families,” said John Wilmoth, director of the U.N. population division. Collectively, the population is growing older, living longer, and having fewer children.

“Humans are incredibly adaptable and can find ways to make it work” Wilmoth said. “The challenge is the speed of change.”

The world’s population is expected to peak at 10.4 billion in 2086, according to projections from the U.N. Population Division.

Even as growth slows, the increase in population well into this century raises important questions over how many people the planet can sustain, especially amid the effects of climate change. As birthrates have fallen dramatically in most wealthy countries, they remain high in many poorer parts of the world, which are least equipped to manage the impacts of continued growth.

Growth declines and an aging population

Populations are declining across the world. Dozens of countries are expected to see at least a one percent dip by 2050, according to the U.N. projections.

Analysts worry about the implications of a shrinking, and aging, workforce.

An older population is “less dynamic, less likely to set up businesses and more reliant on the state,” said Paul Morland, a demographer and author of “The Human Tide: How Population Shaped the Modern World.”

One solution could be changes in immigration policies. In the United States and Canada, for example, lower birthrates have been offset by a growing number of immigrants.

Other economists think this could be a moment for reassessing what constitutes prosperity.

“The growth model we are addicted to is based primarily on producing things,” said Vanessa Pérez-Cirera, director of the Global Economic Center at the World Resources Institute. She noted that more countries could include older people in service roles such as therapists or museum employees.

Concentrated population booms

By 2050, the population is projected to increase by 1.7 billion. Half of that growth will occur in just eight countries: Democratic Republic of Congo, Egypt, Ethiopia, Nigeria, Pakistan, the Philippines, Tanzania and India.

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By next year, India is expected to surpass China as the world’s most populous country.

These swelling populations are a challenge for governments already scrambling to build enough infrastructure. In some of these countries, population growth and fertility rates are declining, but not quickly enough.

Places “where we find very rapid growth tend to be much poorer,” Wilmoth said, and therefore less resilient to climate change. In Pakistan, more than 1,000 people have died since June after heavy rains and mass flooding decimated parts of the country. India saw deadly, unbearable heat this summer that disproportionately affected the millions of people who live without air conditioning.

Population growth over the next 60 years has renewed long-standing questions over how many people a warming world can support.

Unequal distribution of resources

The 18th-century demographer and economist Thomas Malthus predicted that population growth would outpace food production, resulting in famine, drought and war. Advances in agriculture proved Malthus wrong, but today’s experts still fear a food crisis: driven not by overall yields, but by drastic inequality.

“There are enough resources to feed the population today,” said Pérez-Cirera. “But it’s just not evenly distributed.” According to the World Food Program, some 828 million people — more than 10 percent of the world’s population — go to bed hungry every night.

The human footprint’s continued expansion could further harm the natural order — 75 percent of the planet’s ice-free land has been significantly altered by people, according to a 2020 report from the World Wildlife Fund. An estimated two-thirds of mammals, fish, reptiles and amphibians have been lost in the past approximately 50 years.

As the world hits a new population milestone, and the effects of man-made climate change become a fact of life, Pérez-Cirera said it should prompt a collective “moment of reflection.”

“It’s a bit like we’ve grown without thinking,” she said. “Do we want to be the species on Earth that uses it up?”