8 billion humans and counting: What it means for the planet's future

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It took 300,000 years for the human population to grow to one billion souls.

We hit that milestone in the early 1800s. And then, that growth curve took off like a rocket.

Only 200 years later, we’ve grown to 8 billion. And there’s hot debate about what comes next.

“There really only been two camps. There's been this camp that says there are too many people in the world," Jennifer Sciubba says.

"But on the other side, there are folks who say the more people we have, the more potential geniuses we'll have, the more innovation we'll have.”

And that has been true, thus far. But every natural system has a carrying capacity.

“We can either engineer a controlled contraction back to a situation of relative equilibrium with the natural environment, or nature will do it for us as it does with every other species," William Rees says.

Today, On Point: Population growth, economic growth and environmental balance.

Jennifer Sciubba, demographer who focuses on global demographic trends. Fellow at The Wilson Center. Author of 8 Billion and Counting: How Sex, Death, and Migration Shape Our World. (@profsciubba)

William Rees, professor emeritus of ecological economics and human ecology at the University of British Columbia.

Andat Dasogot, head of the Population and Development Unit at the United Nations Population Fund in Abuja, Nigeria.

Winnie Mitullah, professor of Development Studies and chair of UNESCO’s higher education network at the University of Nairobi, in Nairobi, Kenya.

Elizabeth Hadly, Global change scientist at Stanford and Director of the Jasper Ridge Biological Preserve.

Reprinted from 8 Billion and Counting: How Sex, Death, and Migration Shape our World by Jennifer D. Sciubba. Copyright © 2022 by Jennifer D. Sciubba. Used with permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.

On Earth's population of 8 billion and counting

Jennifer Sciubba: "My first thought about hitting 8 billion was that I felt really different about it from when we hit 6 billion people. So when you were talking about when you were in high school and you kind of had this moment where you understood the relationship of people to the world around them. That moment for me was in 1999 when I was a sophomore in college, and my very eccentric professor showed up in class one day and stopped at the doorway long enough for us to look at her. And she was wearing a black armband. And then she started marching in front of our desk, saying that today world population has hit 6 billion people, and this is an absolute travesty.

"She never had children and we should never have children either. I realize that in my lifetime, and I don't like to think of myself as very old. I've already seen us hit 5 billion, 6 billion, 7 billion and 8 billion. And if I take good care of myself, I think I'll see world population peak. So it tells me that we've got a lot of hubris as human beings. There are so many points in our human history where we've written about the sky falling, but the sky has stayed up there. And like the quote you used from the U.N. Population Fund. Life has gotten better for the majority of people on the planet. But, and I think the but is what we're going to unpack here over the next hour."

But ... what?

Jennifer Sciubba: If we imagine our global population growth as two points and they're together and over a timeline, everything is pretty similar around the world, the experiences are similar around the world. They really start to diverge last century. So you can imagine those two points coming apart. Right now, we are at a huge point of divergence. So for people like me ... I'm cozily ensconced in a sound booth nice and warm.

"... But as you mentioned, there are many places in the world where people rely on their immediate environment in order to survive, and they do feel those effects. So we have two very different experiences around the world. To keep it simple, on the one hand, there are a handful of countries that are experiencing rapid population growth, and those will drive global numbers over the next several decades. But on the other hand, two out of every three people on the planet live somewhere with below replacement fertility, meaning below the number needed just to keep the population growth steady."

On areas with rapid population growth 

Jennifer Sciubba: "Yes, we can really identify those places. And certainly it's not the whole region of sub-Saharan Africa. I think actually the really interesting story is to look at how population trends, even within a region that we've lumped together for, for some good reason in the past, has started to diverge. So there are places like South Africa in Botswana that have quite low fertility.

"But we also know that sub-Saharan Africa has some of the highest fertility on the planet. So more than half of the projected increase of total global population between now and mid-century is just going to be in eight countries. That includes some in sub-Saharan Africa. So Democratic Republic of Congo, Ethiopia, Nigeria, Tanzania, they are really driving global growth because their fertility rates are quite high still."

On how we're negatively influencing our planet

William Rees: "I think people tend to forget that the Earth hasn't gotten any larger. And as she mentioned, there's a fixed amount of solar radiation that is fixed by green plants and that is used to support all animal life. So that in just 10,000 years, human beings have gone from being much fewer than 1% of mammalian biomass, to the point that we are now 34%. And if you add other domestic animals, that's another 60 odd percent. So together, humans plus our domestic animals amount to about 96% or 97% of the total biomass of mammals on planet Earth.

"So we're witness to and the cause of a phenomenon that ecologists would call competitive displacement, since there's a limited amount of energy and material in the system. The more humans get less risk for other species. So the growth of the human enterprise is literally pushing the rest of advanced life off the planet. And that's the phenomenon that that she was describing. We're seeing an absolute collapse in insect populations in many places all the way up to advanced mammals. So this is a major crisis. And I think it's really important to understand that when we talk about population, when we talk about, say, climate change, we tend as humans to think in very simplistic reductionist terms. One problem at a time.

"But all of these things are connected in a phenomenon that I call overshoot. The human population and the human enterprise have simply overshot the long term carrying capacity, even for human beings of planet Earth. It's not a question of having to slow down our population and economic growth in the future. We need to begin to think of this right now, because the current population at current average levels of consumption is not sustainable. Because we are currently living by depleting the natural capital upon which we all depend.

"We're depleting the biomass, we're depleting biodiversity, we're destroying our soils, we're overfishing the seas. Everything that we depend on is being reduced by the continued growth of the economy and population. And I think, again, it's very important to keep these things together. Population may have increased by eight-fold in the last couple of hundred years, but the economy in real terms has grown by over 100-fold so that the consumption by humans has massively increased beyond the reach of human population.

"So we now have to begin seriously to think of the phenomenon which is actually becoming very well known in Europe called degrowth. The planned contraction of the human enterprise, particularly of consumption by the wealthy. ... Population is an enormous problem. Consumption is an enormous problem, but population growth stimulates consumption."

On Earth's future

Jennifer Sciubba: "We're moving toward this aging and shrinking world, and we are worried because we can't sustain that same huge level of economic growth in the past. And we do need to think about what that might look like, so we can look relook at concepts like retirement. We can look at concepts like what is work life. We also, though, have to start thinking about family and marriage. And, you know, we're talking about a paradigmatic shift.

"That means we have to look at the world through a completely different lens than we've looked at the world in the past. But all of our theories about the good life, our economic theories, our political theories, those were all developed under conditions of population growth and economic growth, as William said. So it's really hard to get a paradigmatic shift and say, what if we try to look at the world in a different way? Can we look at an aging and shrinking society as a good thing? Can we look at growing older individually as a good thing? We've not been good at that. And so we're kind of taking that negativity and applying it at the societal level."

William Rees: "We have to keep in mind, though, that although fertility rates are falling in some Western countries, if you take Canada in the United States, the populations continue to grow at 1% or so per year. And the addition of every wealthy person to the country, to the population, is the equivalent of, say, 15 or 20 people in one of the poorer countries. So when we hear of the decline of a population such as Japan, that's cause for celebration. It's not cause for despair. Because of the economic implications of that, those are minor problems compared to the problems of overshoot, which are confronting right now.

"The world is in a state of overshoot. We are depleting and polluting the very biophysical basis of our own existence. It is consumption of resources that does that. But population and income growth are important contributors to that consumption. And right now, we can show that even though we diminished population in this conversation, it is the driving factor in much of the world. Countries that are experiencing very rapid population growth, as some of your earlier speakers showed, are just benefiting from that. No one gains because the benefits of economic growth are overwhelmed by the increase in populations.

"And even in rich countries, as I say, the major contribution right now at the margin to environmental impact by those people is from population growth, not income growth, because the average per capita ecological footprints of people has stabilized even in wealthy countries. So yes, it's consumption, but there are two components, income growth and population growth. The world is in overshoot right now. We have to think of reducing both populations and growth, economic consumption."