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Adapted from After the Spike: Population, Progress, and the Case for People by Dean Spears and Michael Geruso. Copyright © 2025 by Dean Spears and Michael Geruso. Reprinted by permission of Simon & Schuster, Inc. All rights reserved.

Imagine a modest, traditional cabin in the woods. It’s on a pretty site — surrounded by pines and on a gentle, south-facing slope. The porch looks out to a mountain range on protected state lands. The view is marvelous, and the nearby hikes are pristine. Water bubbles up from a spring on the land. It’s winter. There’s a wood-burning fireplace, backed up with a buried propane tank for more practical and efficient heating tasks. Stepping out the front door with your coffee, you smell the pine. You might hear the rustling of a snowy weasel or catch a glimpse of a barred owl.

Now imagine a different place to live: a fourth-floor apartment in a mid-rise building, with shared walls on two sides, plus a floor that is someone else’s ceiling and a ceiling that is someone else’s floor. The view from the window is the cracked facade of another building. Water is piped in from a reservoir far away. Like the cabin, a gas furnace heats the building. Unlike the cabin, there’s air-conditioning for the summers. Passing the alley beside the building, you may smell the runoff from a dumpster. Stepping down into the subway station, you might hear the rustling of a brown rat or catch a glimpse of a rock pigeon on an awning overhead. A little Christmas tree air freshener dangling from the rearview mirror of a passing taxi might be as close as you’ll get this week to the sight of pine.

Life in the cabin is more natural, right? Closer to nature, sure, but also worse for it. The cabin is, compared with the apartment, an environmental disaster. The heat lost through the walls of the apartment mostly goes to productively heat the apartments left, right, above, and below it (using less energy per resident). But the heat lost through the walls of the cabin vents wastefully to the open air. To say nothing of the particulate-matter air pollution and higher carbon intensity of burning solid fuels in that lovely fireplace. The seclusion of the cabin means that electricity comes from far away, with significant waste in transmission losses. And of course, the beans for that cup of coffee or marshmallow for that hot cocoa would have a less carbon-intensive path to the big city than out to any remote mountain. You might enjoy glimpsing the local wildlife, but it has no interest in you settling its home. Go take a hike elsewhere, if you please.

Human life is polluting. That one human settlement in the cabin is polluting, disruptive, and dislocating, so intuition might tell us that the impact would scale with population. In particular, it may seem like it should scale in a straight line. If one family on one acre is bad, aren’t ten families together on one acre ten times as bad and a hundred families on one acre — the density of a downtown city — a hundred times as bad?

No, because the consequences of people do not scale in straight lines. It turns out that living together in a dense urban environment generates fewer emissions per person than spreading that same number of people out to far-flung places.

None of this settles what a larger or smaller global population might mean for the environment. The cabin in the woods is merely an example of how an option that in fact emits more carbon could feel like the more environmentally responsible choice. Similarly, for many questions of population growth and decline, what feels right can often run afoul of what the science tells us.

More people does not have to mean more pollution

What does one more child born mean for the environment? The answer is more complicated than “it makes everything worse.” A few decades ago, some of the most pressing environmental concerns in the United States were lead in the air, a depleting ozone layer in the stratosphere, and acid rain. Now, with the benefit of hindsight, we can ask what a larger population has meant for each of these challenges in the decades since.

Mike’s son, Emmet, was born in 2013. Emmet’s life didn’t cause lead concentrations in the air to increase. Emmet has never ridden in a leaded-gasoline vehicle. That’s because people in the United States decided that breathing car exhaust with lead in it was unacceptable. In the 1970s, the U.S. Environmental Protection Agency began phasing out leaded fuel.

Emmet’s life hasn’t contributed to the release of chlorofluorocarbons to tear apart the protective stratospheric ozone layer, either. That’s because the advanced economies of the world essentially ended the use of a long list of CFCs by an international agreement in 1987 (the Montreal Protocol).

Acid rain was a big environmental problem that schoolchildren of the 1990s learned about in their science classes. But when Emmet was born, it didn’t lead to more acid rain. That’s because the U.S. government took regulatory actions to address the sulfur dioxide emissions that were causing it.

A log cabin in the woods may seem more natural given its building materials and proximity to nature. However, it’s worse for the environment due to the inefficiencies involved in living in and maintaining it. (Credit: Thelma Smart / Wikimedia Commons)

Some of the environmental challenges we face today, including climate change, are bigger than those we faced with lead pollution, stratospheric ozone depletion, and sulfur dioxide emissions, where humanity has already turned the corner. And yet, if Emmet someday has a child — Mike’s grandchild — that child could live well past 2100. It could be that they live most of their life after greenhouse gas emissions have turned the corner, too. Maybe even after net emissions have been brought down to zero.

If so, it would be because people in the interim decided to end net greenhouse gas emissions — and developed the policy and infrastructure to do so. That future is available to us to choose, and it has little to do with the number of people on the planet. After all, the technologies, regulations, and treaties that addressed lead pollution, ozone depletion, and acid rain improved the environment while the population was growing.

The implications of one more person for greenhouse gas emissions, for biodiversity, for land use, for particulate-matter air pollution, and for every other urgent priority will depend on what we choose.

Let’s clear the air

The cabin in the woods is a story. The life Mike’s grandchild might live is speculation. Let’s get back to facts, things we can measure and know today. Is more air pollution the straight-line consequence of more people? The data tell us that global average exposure to particulate air pollution has fallen sharply since 2015. All the while, the world added over 750 million people.

“More people, more problems” isn’t what shows up if we compare the past with the present. What about comparing across places instead of over time? The graph below shows the relationship between air pollution and population density. Each dot is a country. For each country, we show the annual exposure to particulate pollution, using a standard measure: the concentration of tiny particles called PM 2.5 , named for their diameter, 2.5 micrometers. Higher in the plot means worse pollution. Farther to the right means more people per square mile.

Across countries, population density is unrelated to particulate air pollution. (Credit: Dean Spears and Michael Geruso / World Bank World Development Indicators)

Air pollution is not completely contained within tidy political boundaries. Wind blows it around — sometimes a long way. And yet, most of its harms happen close to its source. So the figure is informative of what countries choose in their environmental and industrial policies.

The United States shows up at the bottom and toward the left. It is not very dense, nor is it very polluted. Its spacious skies and purple mountain majesties are mostly undistorted by particulate haze, although seasonal wildfires temporarily change the air quality. Conversely, India’s air suffers smoke from coal-fired power plants, crop burning, industry, construction, and more. The country appears among the topmost polluted countries, which would surprise nobody who knows India.

If we had only those two data points, India and the United States, then we’d end up at the wrong conclusion: more people, more pollution. But we are here for data, not for anecdotes or to be misled by incomplete comparisons. Looking over the wider world, the shape of the plot is a disorganized scatter. The relationship between PM 2.5 and population density is no relationship at all. If we were searching for an example to help people visualize what a scatter plot looks like when there is no statistical correlation, this figure would do the trick. Japan and South Korea are about as densely populated as India, but breathe much cleaner air. Niger is less dense than the United States, but has terrible air pollution.

Some low-density places, especially middle-income countries, have high PM 2.5 because they burn coal for power. Lowest-income countries with agricultural economies like Niger suffer high concentrations of air pollution because of burning agricultural waste (there’s no cheaper way for poor farmers to clear their fields ahead of the next planting) and because of burning traditional fuel like wood and dung for cooking and heat. Coal-fired power plants and the practice of burning crops and solid fuels are two of the biggest contributors to PM 2.5 globally.

The implications of one more person for greenhouse gas emissions, for biodiversity, for land use, for particulate-matter air pollution, and for every other urgent priority will depend on what we choose.

People in Japan and South Korea manage to live densely and prosperously without polluting their air. That’s not because Japan and South Korea are somehow offshoring their particulate air pollution — displacing their coal use and crop burning to a poorer country. Japan and South Korea and Europe and plenty of other rich countries have agriculture (a lot of agriculture, in fact). They also use plenty of energy (much more than in the poorer places of the world where coal is burned). They have less air pollution because of the coal and the crops that they do not burn.

In other words, a society can have clean air, economic prosperity, and a large, thriving population without any contradiction. That can happen if the society makes investments and implements rules to keep the air clean. The same can be true when it comes to maintaining clean water or addressing the priorities of climate change.

It is a mistake to think that a shrinking global population guarantees progress on these and other environmental challenges. Population decline isn’t a substitute for direct, targeted approaches to environmental stewardship. Whether more people cause more pollution depends on what those people and their government do.