READ: Data Exploration - Future Population Growth

Over the course of the last school year, you've probably noticed something about population on this planet: there are more of us here than there used to be. We know approximately how many people inhabit this planet today (around 7.7 billion in 2019). We have reasonably good estimates for the recent past (2 billion in 1928; 1 billion in 1803). But, the further back we go, the murkier the data gets. The same is true for the future—the further we travel forward in time, the less certain we can be about how many people there will be on Earth.

For much of human history, the global population was much smaller than it currently is, and it grew at a relatively slow rate. But during the twentieth century, our global population quadrupled. Since then, population growth appears to be slowing down. Though our overall population has continued to rise, the rate of its increase started to decline in the 1960s. Today, the global population grows by about 1 percent each year. You can see these trends illustrated in Chart 1.

Will these trends continue? That's a really important question. Population affects things like available space and resources, which are increasingly limited. The more people there are on Earth, the more food, fuel, space, and materials are needed to sustain them. Think of it this way: The number of people keeps changing, but the planet and the resources on it are a lot more fixed. That's a problem.

That's part of the story. But there's more to it. Humans aren't just stomachs—they're also brains. As our population has grown, so has the pace of innovation in technologies and institutions that have allowed us to use our limited resources in new problem-solving ways. Our recent past has shown that more people can mean more food, new fuels, and more useful innovations. We just might be more brain than stomach.

Whether you think population growth is a problem for the future or might provide solutions to our most pressing problems, it will be central to our future as a species on this planet. Scholars have spent a lot of time trying to predict what our population will look like in the next century. To understand where we might be headed, we need to know where we've been.

As one example, explore the two maps below. Map 1 shows past data (1950–2015) about population growth rate by country. Map 2 uses past data, like that in Map 1, to make predictions about the future (2015–2100) of population growth by country. Note: While exploring these maps, you might see the phrase "medium variant" pop up. Don't worry too much about what it means—just think of it as the most likely scenario.

By exploring these two maps as well as Chart 1, you can see that there are past trends that scholars use to predict the future of the global population. The twentieth century saw huge increases in both our population and the rate at which it grew. More recently, the global rate of growth has started to slow, and we expect that trend to continue. But, by switching scales, we see dramatic differences in the rates of population growth. While Eastern Europe has seen its population shrink in recent years, many countries in Sub-Saharan Africa are experiencing higher than average growth rates. But why has any of this happened? What causes the population size to change?

There are three main factors that affect population growth in a country or region: mortality, fertility, and migration. Just so we're on the same page, let's define them:

Globally, mortality rates have decreased. Child mortality in particular has declined. Life expectancy has increased across the globe. Declining mortality rates have made the population grow. That explains everything, right? The population is growing because people are dying less.

Well, not quite. Remember that while the population is indeed growing, the rate of growth is slowing down. That's partly because although mortality rates have dropped, fertility rates have also gone down. On average, women are having fewer children. That reduces population growth rates. The global average fertility rate was 5 children per woman until the end of the 1960s. Since then, it has been cut in half, with an average of 2.5 children per woman. Fertility is a variable factor. It can change depending on how a society develops culturally and economically. Fertility is particularly dependent on the well-being and social status of women.

So, we have a few different variables that affect population growth: how big a population is to begin with, death rates (mortality), and birth rates (fertility). At the global level, population changes are determined by the balance of only two variables: the number of people born each year, and the number who die. But, at the national or regional level, we need to consider a third variable: migration.

We can consider these variables when trying to understand past population changes and project future population changes. But when we're trying to make projections about the future, there are a few different ways we can do that.

Future projections are really complicated, even for experts. But, for our purposes, it really comes down to whether we think the future will be like the past or not. Are different regions experiencing the same, or different, trends? What will happen to the human population in the future, and what will that mean for the world? You will have the opportunity to explore these questions—and come to your own conclusions—in this data exploration.

Max Roser is the founder and director of Our World in Data. He began the project in 2011 and for several years was the sole author, until receiving funding for the formation of a team. Max’s research focuses on poverty, global health, and the distribution of incomes. He is also Programme Director of the Oxford Martin Programme on Global Development at the University of Oxford, and Co-executive Director of Global Change Data Lab, the non-profit organization that publishes and maintains the website and the data tools that make OWID’s work possible.