2.4 Per Second, a Million Every Five Days

5/16/24

Hello everyone:

I’ve been fighting a cold all week, which means my late night writing hours have been curtailed. I’m bringing you a much updated and rewritten 2021 Field Guide essay, thanks to a cue from a new reader who asked me why I don’t write about human population. Those of you who have been with me long enough know that I’ve written quite a bit on the topic, but it’s been a year and a half since the last essay. It’s a good time to introduce new readers to that work.

As always, please remember to scroll past the end of the essay to read this week’s curated collection of Anthropocene news.

Now on to this week’s writing:

Let’s talk about a difficult topic: the unsustainable growth of human population. It’s not a topic that wins friends or votes, but it’s a fundamental feature of the Anthropocene. Simply put, it would not be possible for our species to breach multiple planetary boundaries with our population of just a century or two ago.

My purpose here is to clear the air around what can be a toxic discussion and to introduce you - if you’re not already familiar - to the numbers and to what I firmly believe is a rational way to understand them.

I’ve written other essays on population, including another one from 2021 on Earth’s carrying capacity, and two from 2022 on the declaration from the U.N. that human population had reached 8 billion. Those writings carry the ideas and arguments here much further. Please take a look.

In talking about population and overpopulation, there are some hard questions to sort through. Particularly this one, about the future: Would population still matter if we eliminated fossil fuel use, farmed responsibly, ate mostly plants, reduced consumerism and consumption, restored and regenerated landscapes and at-risk species, and created an equitable global society which did not reward wealth and punish poverty? In other words, would population matter if humans treated both the Earth and each other with a full measure of respect?

I would argue that it does. There are simply far too many of us, consuming far too much within the limited confines of the planet, with at least another billion or two on the way. We’ve taken too much already. Extinction rates are soaring, and we’ve deeply disrupted the atmosphere, oceans, and continents. Even if we limited our erasure of Earth’s biosphere to current levels, and redistributed wealth and consumption evenly among the 8.1 billion existing humans (or the 9 to 10 billion we’ll soon have), it would still be too much. An equitable excess is just as harmful as an unfair one.

But let’s back up. I need to acknowledge a few things. First, that talking about population has a long, ugly racist history linked to eugenics and other violations of basic human dignity. Second, many people falsely assume that proposals for slowing population growth or reducing population necessarily pit human reproductive rights against state control. And third, there is an obvious hypocrisy when affluent nations worry about birth rates in developing nations.

These deserve essays (and books) on their own, so I’ll just say here that the environmental impact of a few hundred million rich people drowning in excess consumption has always been a bigger problem than a few billion poorer folks struggling to survive; that population reduction and fully-funded voluntary family planning go hand-in-hand because educated women generally want smaller families; and that the racist roots of the environmental movement will always haunt its opinions on population unless we actively reject those roots.

screenshot of Worldometer population clock, 12:12 a.m., 5/17/2024

For now, I want to focus on the raw numbers. And to help me do that, I’d like each of you to open the Worldometer population clock in another tab. If you scroll down the population clock page, there’s plenty of demographic info to keep you busy. But for now, just watch the clock for a while. It has an odd little stutter, like a salsa rhythm, with one step back for deaths and two steps forward for births. The births are relentless: an average 2.4 additional souls per second.

To my mind, there is nothing quite as disturbing as keeping an eye on the pop clock as it spins like a gas pump dial while I go about the various mundane tasks of my day. (Don’t worry too much about me; I don’t do this often.)

Once you have that set up, you should know a little bit about it. The Worldometer clock is an algorithmic estimate of human population, based on demographic science done by the U.N. Population Division of the Department of Economic and Social Affairs and the U.S. Census Bureau Population Division. As Worldometer notes, the “current world population figure is necessarily a projection of past data based on assumed trends,” all of which is regularly updated.

In other words, there’s no army of volunteers with clickers marking each birth and death in every home and hospital on the planet. The main thing to note is that this is a carefully estimated measure of net growth – births minus deaths.

With about 144 additional people arriving per minute, if this essay is a fifteen-minute read for you it would also be a 2160-person read.

At a rate of 220,000 new arrivals per day, that’s the equivalent of a city of a million people – Odessa, for example, or two Atlantas – appearing every five days, the population of Vienna every two days, Los Angeles every twenty days, and another Beijing every 101 days. Each year, another 8.8 New Yorks.

Nearly all of this growth has occurred in the last two hundred years.

One of the finest and most influential scientists of the last few generations, E. O. Wilson, wrote in a 2002 article for Scientific American, “The Bottleneck,” that “The pattern of human population growth in the 20th century was more bacterial than primate.” That is, we’ve looked a lot more like microbes in a well-fed Petri dish, doubling our numbers in a flash, than like the low, stable ape population that we were for millions of years.

Modern humans appeared 200,000 years ago, and the shift from hunt-and-gather to settlement began about 12,000 years ago. However you define human history, it took all of human history, until 1804, for us to reach one billion, but just 219 years later we passed 8 billion like it was standing still.

Beyond bacteria, the other analogy for our recent growth that comes to mind is a wildly successful invasive species – zebra mussels, kudzu, earthworms, cane toads – all of which, not coincidentally, were spread by our wildly successful selves as we’ve shuffled species across continents like cards during a poker game.

Wilson continued: “When Homo sapiens passed the six-billion mark [in October of 1999] we had already exceeded by perhaps as much as 100 times the biomass of any large animal species that ever existed on the land. We and the rest of life cannot afford another 100 years like that.”

As I’ve noted here several times, and no doubt will again, it’s been calculated that 96% of all mammal biomass on Earth today are humans and our livestock. All those wild mammals you love and admire in photographs, videos, documentaries, or books – whether elephants and whales, caribou and beavers, cougars and wolves, camels or bears – now represent only 4% of the total mammal biomass. Likewise, poultry biomass is three times greater than that of all wild birds. We and our livestock outweigh all of the planet’s vertebrates, other than fish.

Which gets to one of my essential points. The question of overpopulation isn’t merely a math problem about how many humans the planet can support. I will not ask the ridiculous, irrational question of What’s the maximum number of people we can squeeze onto the Earth? I am only interested in the rational pursuit of how to stabilize planetary systems so that all life, including humans, can thrive.

Any debate about human population that obscures or ignores the cost to the rest of life on Earth isn’t worth having, in part because all life deserves to live in some version of a global, diverse abundance, and in part because for our sake it must exist. We’re crazy to think we can live without it.

We think we live in a house, car, and office, but those are just our clever snail shells within a living, breathing, interdependent biosphere. We’re still creatures of forest and field. The problem is that we’re erasing the forests and fields.

This isn’t (or shouldn’t be) a radical idea. The science of our reliance on biodiversity for our species’ survival, from pandemics to pollination to public mental health, is clear. E. O. Wilson writes in his book, The Future of Life, that “Perhaps the time has come to cease calling it the ‘environmentalist’ view, as though it were a lobbying effort outside the mainstream of human activity, and to start calling it the real-world view.”

In the we-broke-it-we-bought-it tragedy of the Anthropocene, we now have the responsibility of managing the planet. Which means managing ourselves, including our population.

Thus, the real-world view of population numbers matters too, unless there’s some way to magically reduce the impact of 8, 9, or 10 billion people to the impact of a population level that predates the large-scale erasure of plants and animals. (That’s a discussion for another day, one that explains the battleground between decoupling and degrowth, but for now you can read an excellent recent Aeon article about it.)

Tesla factory in Shanghai - source: InsideEVs

The numbers matter because what we think of as the daily needs of more than 8 billion people (defined and expressed very differently in poor and rich nations, of course) are unraveling the planet. A 2020 analysis published in Nature found that, astonishingly, man-made stuff now outweighs all of life on Earth. The authors measured our output of several substances – concrete, asphalt, brick, glass, metal, plastics, and wood/paper products – over the past century and found that by 2020 our stuff had drawn even with the weight of all life. Plastics alone outweighed all land and sea animals.

And the study’s accounting didn’t add in all the waste from producing these daily materials, nor did they add in the weight of humans, our livestock, our crops, our earthworks and mining waste, or the fossil-fuel production of our atmospheric CO2. The mass of CO2 alone, if added, would mean we began to outpace the production of nature back in 1996. It’s hard to imagine a gas having so much mass, but not if you remember it’s being produced by billions of people burning tens of millions of years of stored fossil fuels in just a few decades.

The numbers matter because even though global population growth rate has slowed considerably, any growth upward from 8 billion happens incredibly fast. The current global growth rate is 0.91% per year, down from the all-time high of 2.06% just after I was born in the late 1960s. But today’s seemingly minuscule 0.91% growth rate adds about 73 million additional humans every year – more than the population of Thailand – just as in 1970, when fewer than half the people at double the rate added another 72 million.

The numbers matter because as individuals, cultures, nations, and civilization generally turn slowly to face and respond at least halfheartedly to the climate and biodiversity crises that our growing population and consumption have created, we have to do so in the context of another Thailand of babies arriving every year.

Look again at the Worldometer pop clock for a moment and think about a particular environmental issue that matters to you. We’re making incredible strides with renewable energy, but how much harder is it to limit CO2 emission in the context of that spinning wheel, as global trade and agriculture and AI expand to meet our needs and desires? How much harder is it to provide food and clean water and housing and cooling to everyone in a rapidly heating climate? To protect migratory birds and pollinators in rapidly developing nations? To reduce extinction rates and fishing pressure? To protect coral reefs? To shield entire ecosystems from any future resource extraction?

Here’s E.O. Wilson one more time, from the “Bottleneck” article:

“The constraints of the biosphere are fixed. The bottleneck through which we are passing is real. It should be obvious to anyone not in a euphoric delirium that whatever humanity does or does not do, Earth's capacity to support our species is approaching the limit.”

from Population Matters

The numbers matter because even a tiny tick upward in global fertility rate explodes the prospects for dealing with these crises. The current global fertility rate is 2.32 births per woman, down from 5.32 births per woman at the 1963 peak. (A 2.1 fertility rate is considered zero-growth or “replacement rate,” i.e. two children replacing their parents, with the 0.1 added on to account for infant and child mortality.) This much lower rate reflects decades of good work with family planning and improving educational prospects for people around the globe. The U.N.’s current median projection for human population by the year 2100 is about 10.4 billion, lower than previous estimates.

But should fertility rates jump up by half a child per woman, the prediction climbs sharply toward 15 billion just eighty years from now. I don’t think anyone expects this, but like the lights of a runaway train it gets your attention.

Alternatively, if the global fertility rate dropped by half a child to 1.8, population in 2100 would be expected to drop to roughly 7 billion, which we first reached back in 2011.

A quick note about projecting population in 2100, or even 2050: No one knows how it will play out. Human demographics are complicated, particularly in the Anthropocene. Cultural attitudes and national policies matter. Plus, as the world heats and transforms, we don’t know if people will continue to live longer lives, what changes there might be in child mortality, or how women will determine when to begin having children and what size family they desire.

We don’t know what kind of turbulence, at a global scale, will impact the capacity or desire of humans to produce and care for children over the next several decades. Massive waves of climate refugees, for example, or a drop in global crop yields, or political upheaval in the face of such challenges, could have major impacts, as would a pandemic more prolonged or mortal than the current one.

More cheerfully, if today’s efforts to provide comprehensive (voluntary) family-planning services and long-term education to girls and women were fully funded, fertility rates would drop and bend the 2100 trend lines in the right direction. And if the world got serious enough to keep warming to, say, 2.0C, that might reduce would-be parents’ concerns about having children. (A 2021 survey found 40% of young adults around the world were hesitant about having kids in the midst of the climate crisis.)

For now, we have to assume that current trends are a reasonable guide but that updates will be necessary. Earlier U.N. demographic projections for 2050 and 2100 were different than the new ones, and there are other predictions which are different even now. Both the Wittgenstein Center World Population Program and a 2020 study in the Lancet project that global population will peak around 2070 at 9.7 billion and then drop to 8.8 billion by 2100. The predictive gap between 10.4 and 8.8 billion at century’s end is larger than the population of either present-day India or China, but that’s the uncertainty we have to live with and plan for, until better data arrive or some vast upheaval occurs.

It’s tempting to look at the SARS-CoV-2 pandemic as another kind of population-altering upheaval. But human population has become an extraordinarily massive ship - weighing as much as most vertebrate life on Earth – to try to turn. Global deaths from the pandemic are officially counted at 7 million but the Economist estimates the true number is between 18 and 35 million. Setting aside the reasons for such disparate estimates, for our purposes here the difference is one to six months. That’s how long it took to “replace” the pandemic dead, statistically speaking, at 2.4 babies per second.

Even if a billion people perished in some kind of unthinkable scenario, the last fifty years of population growth suggests that, assuming civilization continued as normal, they would be “replaced” in about twelve or thirteen years. This is a grotesque bit of data with too many variables to make sense of, so I’ll move on. I note it only to reinforce my point about the scale of population and its continued growth, even as the growth rate has declined.

The path forward, of course, is through a voluntary reduction in birth rates rather than increased mortality. The good news is that, as of 2024, 129 nations have fertility rates at or below replacement levels. Again, this drop has come as the result of the choices women and families have made, not (China notwithstanding) because of draconian government restrictions. If the world had a fertility rate like those in Taiwan (1.1) or Spain (1.3), population would drop sharply by the end of the century. In that time, Spain is expected to decline from 47 million to 33 million; Taiwan, likewise, is predicted to drop from 24 million to 16 million.

I should note that there is a lot of fear about population decline. Economists, nursed on the fairy tale of constant growth, are generally bewildered by it. Governments have few ideas for how to cope with it, other than to beg women to have more babies. Nationalists and racial purists see it as a direct threat to their dignity.

But a real, deep, and abiding reduction in human population is coming, though perhaps not soon enough for many other species on Earth. Societies will have to restructure and reimagine and innovate, which is what societies have always done. All this deserves more writing another day, but for now just note that as the 21st century tells its tale there will be a very strange and noisy tension between the ecological need for population decline and the corporate clamor for more babies to feed the economy.

If someone making the economic argument questions the value of providing educational opportunities and family planning services to girls and women across the world in the pursuit of population reduction, maybe remind them that nearly half of pregnancies around the world are unintended and that, according to UNICEF, there are still 650 million child brides in this thing we call civilization.

I recommend you read this very short essay, “Ecology and Empowerment,” by Celine Delacroix. (And check out this excellent post/video from

Andy @Revkin

, where I found it.) Delacroix’s essay is part of a 2022 Canadian forum, “The Population Debate Revisited,” and makes a clear case for why population matters to the global ecological crisis and why one of our best solutions is empowering girls and women through education and family planning options:

When reproductive rights are fulfilled, it is well-documented that fertility levels tend to decrease. For this reason, empowering all to decide the number, spacing, and timing of their children would thus not only fulfill an internationally recognized reproductive right, but would also help human beings achieve a better balance with the environment…

All interventions likely to have lasting positive effects on population trends are based on steps taken for other good reasons: education for women and girls, comprehensive sexuality education, expansion of women's rights, and unfettered access to effective family planning services and commodities. If the public better understood this key fact, addressing population would gain attention and acceptability as an important public topic and a noble cause deserving global effort.

Finally, let’s take one more look at the Worldometer clock, and remember that there is extraordinary meaning in each tick and each tock, each life gained and each life lost, in the great embracing tangle of love and grief we call existence. These lives that turn the dial are a) as vital as our own and b) as beautiful as those of cedar trees and migrant hawks and spores and anemones. And the best way to honor the production of vital, beautiful life - human and more-than-human - is to give it space on Earth to thrive. Which means reducing the space we’re taking.

The details of how we do that is a question for another day, but perhaps I’ve made the start of a decent case for why we should do it.

One final note: If you’re looking for a way to help nudge the numbers lower, you can fund efforts for family planning and the empowerment of girls and women everywhere. Good places to start are here, here, and here.

Thanks for sticking with me.

In other Anthropocene news:

From the Colorado Sun, some great news for wetlands protection. After last year’s ecologically catastrophic decision by the U.S. Supreme Court to limit Clean Water Act (CWA) protections, lawmakers in Colorado have decided to reestablish those protections. SCOTUS conservatives, with an incredible ignorance about basic natural systems, claimed that the CWA only protected waterways that flowed year-round and wetlands connected to flowing water above ground. (I wrote about this in “The Supreme Court and the Swamp.”) Colorado is the first state in the nation to clean up this mess. Their action will protect thousands of wetland acres, and miles of ephemeral streams. What is your state doing?

From Reasons to be Cheerful, the remarkable return of beavers to London, where they’ve been absent for 400 years. The reintroduction within city limits is still quite small, but it’s part of ambitious work to rewild Britain, one of the most ecologically damaged nations in Europe.

From the Guardian, restoring 170 bison to Romania’s forests may sequester enough carbon to erase the emissions of 1.9 million gas-burning cars. This is part of a growing body of research demonstrating that rewilding and ecosystem restoration are vital for both life and the climate crisis.

Also from the Guardian, a lovely story of a retired woman’s conversion of her front lawn in residential Los Angeles to a vibrant garden that helps feed her neighborhood. The conversion was done by Crop Swap LA, whose slogan is “We Grow Food on Unused Spaces.”

From Inside Climate News, the catastrophic heating that hit 30% of Earth’s oceans – an area the size of Asia, Africa, North America, and Europe – caused massive die-offs and triggered a deep abiding grief in many ocean scientists.

From Zero Carbon Analytics, the International Energy Agency has lowered – again – its long-term forecast for methane (liquefied “natural” gas) markets. May this trend continue to sharpen downward.

From Mother Jones, a project to bring vital naturalist data to anyone who wants it, including you. The majority of the untold millions of animal specimens stuffed into museum drawers, cabinets, and storerooms are never put on display or available for the public to study. This is especially true of specimens taken by colonial powers from poorer countries, where today’s researchers and students don’t have access to samples of their native species. Now the openVertebrate Project is CT scanning tens of thousands of vertebrate specimens and putting all the data online. Already, hundreds of peer-reviewed studies around the globe have cited the information. The article highlights the African spiny mouse, which until now had been hiding special regenerative scales which may prove useful in helping medical researchers figure out how humans can regenerate cells and organs.

From Science Friday, an article and podcast on the “green glacier” of trees spreading quickly across the U.S. plains and threatening the last remnants of tallgrass prairie. It’s a difficult, perhaps intractable problem with an Anthropocene solution: cutting down every tree and woody shrub, and burning often to keep them from returning. Meanwhile, the Amazon rainforest is on the cusp of converting from forest to grasslands.

Take half an hour to watch Kelp!, a fun and informative documentary about kelp-farming on the UK coast. A motley crew of young folks sail the coast talking to pioneering, optimistic kelp farmers who are actively working to promote aquaculture that can sequester carbon, rebuild coastal biodiversity, sustain fishing communities, and perhaps even help replace plastics.