On November 15–as estimated by demographers–the count of humans on this planet reached eight billion. Over the past few decades, population growth has been steady with billion-person marks appearing every dozen years. This is changing. Growth is beginning to slow, and experts predict the world’s population will top out sometime in the 2080s at about 10.4 billion.
This slowdown is partly due to a shift towards fewer offspring, a phenomenon that is occurring almost everywhere, but at different rates. The lowest birth rates are currently found in high-income countries. However, the reverse is true: the highest birth rates lead to lower incomes. Jennifer Sciubba, a Rhodes College social scientist, says that the gap between rich and poor nations has continued to grow. She has written extensively about these global-scale demographic shifts. “But we’re moving towards convergence” Longer term, this means that the current disparity in birth rates between nations isn’t permanent. It’s temporary and will shrink over the next decades.
Major demographic factors, including migration, mortality, and longevity, all contribute to the world’s population fluctuations. However, focusing on fertility can help to explain why the number of human beings on Earth seems to be falling. Demographers define fertility to be the average number of live births per woman in a given region or country. In the accompanying graphics, the term woman is used to refer to anyone who was born as a woman. For example, the U.S. has a fertility rate of 1.7 while China’s is 1.2. Demographers consider a fertility rate of 2.1 the replacement rate, which is the minimum number of offspring required for a population to remain stable. Today, the replacement rate is lower than the birth rates in the richest countries. Most countries around the globe will follow the example of the wealthy over the next decades. Here’s what that might look like.
In 1960, when the world’s population was three billion, nearly every country had fertility rates above 2.1 live births per woman.
But that started to change over the following decades. The fertility rate of a country is usually correlated with its average income. While wealthier countries were the first to adopt a trend toward fewer offspring than their average income, lower-income countries are also following this trend.
Here is the picture as we reach eight billion.
Fertility was especially different in higher- and lower-income countries from the 1990s through today. However, by the end century, fertility rates will be lower worldwide.
These numbers give insight into how and where the population growth rate is changing. Humanity’s future depends on many other factors than fertility. People in wealthier countries may have fewer children but their offspring tend to use more resources. This means that rich countries can still have large planetary impacts despite having fewer people. Organizations like the United Nations Department of Economic and Social Affairs, which tracks and predicts human populations, are working towards policy-based solutions to ensure that everyone can live healthy, fulfilling and sustainable lives. It is crucial to have a clear understanding of the population shifts in order to achieve a bright future.
