Earth now has 8 billion people—and counting. Where do we go from here?

From the emergence of Homo sapiens, it took roughly 300,000 years before one billion of us populated the Earth. That was around 1804, the year morphine was discovered, when Haiti declared independence from France, and when Beethoven first performed his Third Symphony in Vienna.

We’ve added our most recent one billion more just since the first term of U.S. President Barack Obama. Based on the best demographic projections, the United Nations estimates that the planet will reach eight billion people in the next 12 years, just 12 years after reaching seven million.

The timing of this is not known. Census data can be decades old in some parts of the world. During COVID-19 it was virtually impossible for some countries to record every death. Even the most sophisticated computer models can be off by as much as a year. It’s not like anyone has done a global head count.

But the UN is declaring November 15 as the “Day of Eight Billion” because there is no mistaking the import of this moment. People are living longer because of better health, cleaner water, and better sanitation. Irrigation and fertilizers have increased crop yields and improved nutrition. Many countries are seeing an increase in the number of children born and fewer deaths.

The challenges we face as the world population continues to grow are also significant. Many areas of the oceans are being degraded by pollution and overfishing. As humans destroy forests and other wildlands to develop agriculture and commercial products made of trees, wildlife is rapidly disappearing. A changing climate, driven by a global energy system still overwhelmingly powered fossil fuels, is rapidly becoming the greatest threat to biodiversity, food security, access to water for drinking, and farming. This is in addition to the existing population.

The risks and opportunities of the parallel resource crisis and population boom are largely determined by decisions we have not yet made. Which will determine our future? The billions of hungry people we’ll need to feed or the billions of brains we have available to do so?

” The exact effects on future human life are still not known,” says Patrick Gerland, who oversees the United Nations Department of Economic and Social Affairs’ population estimates.

” “So far, the experience is that the whole world has been successful at adapting and finding solutions for our problems,” Gerland states. “I think we need to be somewhat optimistic.”

But he quickly concedes that climate change is a powerful threat. He says, “Simply maintaining status quo and doing not do anything is not an option.” “Regardless of our feelings, changes will occur and the situation won’t improve by itself. There is a need for current and future interventions.”

In the meantime, our overall population explosion belies vastly different types of demographic change taking shape around the globe. The world’s top demographers aren’t in agreement on where we’re headed.

Population changes vary dramatically

The world is facing the likelihood of huge population explosions and collapses at the same time. The most important are on opposite sides.

Perhaps as soon as this year, for the first time in two millennia, China will no longer be Earth’s most populous country, as India finally surpasses it. Even before China’s one-child policy, which went into effect in 1980, “births in China have been declining almost continuously,” Gerland says. In the 1970s alone, the birth rate dropped by half. With better education and career opportunities, more women delay childbirth and there are fewer women of childbearing age.

These trends accelerated during the pandemic. There were 45 percent fewer children born in 2020 than in 2015. China’s birthrate is far lower than the United States.

Even with one of the longest life expectancies of any country, at 85 years, China’s population of 1.4 billion is expected soon to begin declining–in fact that decline may already have started. Since a decade, the workforce has been shrinking. It is now that there are only two workers to support every child or retiree. In the next quarter century, the country will likely see 300 million people over the age of 60, straining government resources, according to a report in Nature. The cost of health care is expected to double.

In Africa however, trends are moving in the opposite direction. The Sahel is experiencing rapid population growth. Nigeria’s median age is just 17, less than half that of China. Birth rates there are falling, too, but remain 20 times higher than in China. Food security is already a concern. More than one third of the country live in extreme poverty, a higher number than any other country except India, which is sixfold larger. One third of all households have one adult who must eat less than the rest in order to provide food for their family.

Currently at 216 million, the country’s population by some estimates could quadruple by the end of the century. By then it could have more people than China, which has 10 times more land. However, this all depends on the childbirth rates. These projections are based on assumptions. Reality could be very different. Education is the biggest driver of falling birthrates, especially for girls. A decade ago, researchers determined that increasing access to education could slow global population growth by one billion by mid-century. How much and how fast we expand those educational opportunities over the next several decades are among the important unanswered questions that will determine how many of us will be living on Earth as we approach 2100.

Predicting the world’s population is complex

Gauging population in the near-term isn’t terribly controversial. “The majority of the people that will be alive in 2050 are already alive today,” Gerland says.

The UN, a group of scientists at the University of Washington and other experts from Vienna, Austria tend to agree on the next quarter century. Based on past events, it seems unlikely that we will see another global pandemic as soon as we have. Despite the recent crisis in Ukraine, demographers do not foresee a global mass migration of people by mid-century. Experts predict that the world’s population will reach nine billion by then.

After that, projections vary greatly. A few years ago, the UN estimated that by 2100, the globe’s population could balloon to 11 billion. Earlier this year, it revised those estimates downward, to about 10.4 billion, thanks to progress in reducing the average number of children born per family. At the International Institute for Applied Systems Analysis, in Vienna, researchers in 2018 projected the population could rise to 9.7 billion in 2070 and then fall back to around 9 billion by century’s end. They used different assumptions and consulted global experts to help them make their predictions. Anne Goujon is the population program director at IIASA. “The main story isn’t just about fertility, but about progress in combating child and infant mortality,” she says.

Meanwhile Seattle’s Institute for Health Metrics sees population peaking at roughly 9.7 billion in 2064, but dropping down to 8.8 billion, possibly less, by century’s end. Nearly two dozen countries, including Spain and Bulgaria, could see their population drop by half. The difference in birth rates is due to a complicated method that researchers use to predict future birth rates.

All of the researchers agree that attempts to incorporate climate change into future population projections are insufficient. Partly because the potential impact of climate change on future population projections is dependent on how fast the world reduces its greenhouse gas emissions. Part of the problem lies in assessing climate impacts. Extreme heat could render parts of India, sub-Saharan Africa and the Middle East uninhabitable. Food security could be impacted by storms. How will people react to sea-level rise in coastal areas that are densely populated?

” “No one is doing it in the right way at this moment,” Stein Emil Vollset, who oversees IHME’s population estimates, says.

Aside from global population estimates and politics, it is likely that migration between countries will be influenced greatly by climate change and politics. The U.S. and Western Europe have seen a large increase in their population through immigration, which has also become a political hot topic. Japan and other countries with declining populations have been more reluctant to accept immigrants. Despite the lopsided trend between declining and booming populations, which is exacerbated by climate changes, it will almost certainly increase migration pressure almost everywhere.

“The only way we can get out of this demographic imbalance,” Vollset says, “is well-managed international collaboration.”