At one point, the valley was a serene, marshy land.
Tall grass and palm trees cast intermittent shadows on the water below. Fish lurked cautiously from the edge of the mangroves.
Orangutans searched for fruit with their leathery fingers. Then the sleeping giant awoke from his sleep.
It was around 72.000 BC on the island of Sumatra, in Indonesia.
The eruption of the supervolcano Toba has occurred and is considered the largest such event in the last 100.000 years.
A series of thunderous explosions spewed 9,5 quadrillion kilograms of ash, gushing in clouds that darkened the sky and rose 47 kilometers into the atmosphere.
After all, vast expanses across Asia were covered with a layer of soft dust three to ten centimeters thick.
It choked water sources and stuck to vegetation like cement - deposits from Toba have been found as far away as East Africa, 7.300 kilometers west of the point of eruption.
But, most important of all, some scientists believe that this eruption plunged the world into a volcanic winter that lasted for decades - and almost wiped out our species.
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In 1993, a team of American researchers studied the human genome in search of traces of our distant past and discovered an indicative signature of a major "population bottleneck" - the moment when humanity shrank so much that all subsequent generations outside of Africa were significantly more closely related.
Later studies showed that during this critical period, which could have been 50.000 to 100.000 years ago, our collective numbers dropped to as few as 10.000 people—the equivalent of the current population of a sleepy settlement in Elkhorn, Wisconsin, or the number who attended a single drive. -in a wedding in Malaysia 2020.
The least affected part of the world was Africa, where genetic diversity remains high to this day - on this one continent there are more genetic differences between certain groups than there are between Africans and Europeans.
Some believe that this coincidence is not a coincidence - they believe that the eruption of the Toba volcano is responsible for it.
That idea is categorically contested, but there is no doubt that most of humanity descended from a relatively modest number of our super-tough ancestors.
From time to time, the inhabitants of entire regions of the world found themselves in great danger.
Flash forward 74.000 years and our once obscure species of hairless ape has experienced a population explosion, colonizing nearly every habitat on the planet and affecting even its most remote corners.
In 2018, scientists discovered a nylon bag 10.898 meters below the surface of the ocean at the bottom of the Mariana Trench, while another team recently discovered "eternal chemicals" that are man-made on Mount Everest.
No part of the world has remained impeccably clean - every lake, forest or canyon has been touched by human activities.
Our sheer numbers and ingenuity have enabled humanity to achieve feats that no other animal could even dream of.
Splitting atoms, sending complex equipment nearly 1,6 million kilometers into space to observe planet formation in distant galaxies, and contributing an astonishing variety of artwork and culture.
Every day we collectively take 4,1 billion photos and exchange between 80 and 127 billion words.
On an eerily specific date, November 15, 2022, the United Nations predicted that there would be eight billion people alive on the planet at the same time - and up to 800.000 times more than survived the Toba volcano disaster.
Today, the population is so large, with so little genetic diversity - outside of Africa - that one researcher recently noted that it's no surprise that some people look eerily like perfect strangers.
There is a limited gene pool that is constantly recycled, and every day about 370.000 new opportunities (in the form of newborn babies) for these genetic coincidences occur.
But with the enormous expansion of humanity came great divisions.
The increase in the number of the Earth's population is perceived by some as an unprecedented success - moreover, there is an increasingly strong school of thought that we actually need even more people.
In 2018, billionaire Jeff Bezos predicted a future in which our population would reach the threshold of a new decimal, in the form of trillions of people scattered across our solar system - and announced that he was planning ways to get there.
During this time, others, such as the British presenter and natural historian Sir David Attenborough, called our encroaching masses "a plague on Earth".
According to this view, almost every environmental problem we currently face, from climate change to biodiversity loss, water scarcity and land conflicts, can be traced back to our rampant reproduction over the past few centuries.
In 1994, when the global population was only 5,5 billion, a team of researchers from Stanford University in California calculated that the ideal size of our species is between 1,5 and 2 billion people.
So, is the world currently overpopulated?
And what could be the future of humanity's global dominance?
The debate over the ideal number of people on the planet is more divisive and emotional than ever, but time is slowly running out to make decisions about the best course of action.
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An ancient concern
At the end of the eighties, in central Iraq, a team of archaeologists from the University of Baghdad excavated a ruined library in the ancient city of Sippar.
Among all that sand, dust, and ancient walls, they discovered 400 clay tablets—records that had lain forgotten in their scholarly tomb for more than three and a half thousand years, still on the same shelves where Babylonian hands had first left them.
But four in particular were truly special.
They contained missing pieces of the story found in fragments on separate tablets scattered throughout Mesopotamia, which still intrigue historians to this day.
"Not even 1.200 years have passed since the beginning of mankind, when the earth expanded and people multiplied..." reads the Atra Hasis - an epic poem carved into clay by an anonymous writer sometime around the 17th century BC
It's the Mesopotamian version of the ubiquitous Great Flood story, found in countless forms in cultures around the planet, in which civilization was destroyed by some deity—and it may contain some of the earliest references to overpopulation in historical writings.
In this ancient story, the gods grew tired of all the "noise" and "hustle" made by the human hordes, as well as the "earth roaring like bulls" from the pressure put upon it by the lusts of our species.
The god of the atmosphere Enlil decided to set in motion several catastrophes to reduce human numbers again - setting up plagues, famines and droughts to arrive at regular intervals of 1.200 years each.
Fortunately, another god saved the day - this time.
But then Enlil planned a great flood instead... and the classic story of building the ark ensues.
At the time Atra Hashis was written, it is estimated that the population of the world was between 27 and 50 million people, equivalent to the number of people currently inhabiting Cameroon or South Korea, or 0,3 - 0,6 percent of those who inhabit this planet today. they call home.
Over the next millennium, scholars became relatively silent on any concerns about population.
Then in Ancient Greece they started to deal with this issue again.
The philosopher Plato held some firm positions.
After a period of rapid growth, during which the population of Athens doubled, he complained:
"What remains now is like the skeleton of a body ravaged by some disease; the rich land has been carried away, and now only the bare outline of the district remains."
Not only did he believe in strict population control, enforced by the state - he ultimately concluded that an ideal city should have no more than 5.040 citizens, and he thought that establishing colonies was a good way to deal with any excess - but also believed that spending must be taken care of.
In Plato's seminal work The Republic, written around 375 BC, he describes two imaginary polises—administrative regions governed almost like small states.
One is healthy, while the other is "luxurious" and "feverish".
In the latter, the population excessively consumes and devours resources, indulging in consumerism until it "exceeds the limits of its own needs".
Alas, this morally bankrupt city-state eventually resorts to conquering neighboring countries, which of course escalates into war - it simply can no longer support its large, greedy population without additional resources.
Plato touched on a question that applies to this day: is the problem the human population or the resources it consumes?
It took more than five centuries after Plato for the global scale of our population explosion to become apparent.
The writer Tertullian, who lived in the Roman city of Carthage, greatly anticipated contemporary observations about our destructive multitude.
In the year 200, when the total population reached 190-256 million - about the number that currently inhabits Nigeria or Indonesia - he believed that the entire world had already been explored and that humans had become a burden on this planet, "..because nature can no longer bear with us".
Over the next 1.500 years, the global human population more than tripled.
In the end, this reserved concern turned into a real panic.
Thomas Malthus, an English cleric prone to pessimism, enters the scene.
A glorious work, Essay on principles of population, published in 1798, opened with two important observations - that all men must eat and that all men love sex.
Taken to their logical conclusions, he explained, these simple facts ultimately lead to the conclusion that humanity's demand will deplete the planet's supplies.
"Population, when not controlled, increases by geometric progression. Food increases only in arithmetic proportions. Even a slight familiarity with numbers will show how much the first power is superior to the second," wrote Malthus.
In other words, a large number of people leads to even more offspring, in a kind of positive feedback loop - but our ability to produce food does not necessarily accelerate in the same way.
Those simple words had an immediate effect, awakening inexhaustible fear in some and anger in others, which will continue to reverberate through societies for decades.
The former felt that something had to be done to prevent our numbers from getting out of hand.
The latter felt that limiting the number of people was absurd or unethical, and that every effort must be made to increase the food supply instead.
The pro-fewer camp was particularly critical of the English Poor Laws passed hundreds of years earlier, which involved paying those living in poverty to help care for their children.
It was speculated that this encouraged people to have larger families.
At the time Malthus's essay was published, there were 800 million people on the planet.
Contemporary concern about the overpopulation of the planet arose, however, only in 1968, when Stanford University professor Paul Ehrlich and his wife Anne Ehrlich wrote The Population Bomb together.
The inspiration was the Indian city of Delhi.
One evening, they were returning to the hotel by taxi and passed through a neighborhood with Udzerica, where they were shocked by the massive amount of human activity on the streets.
They wrote about the experience in a way that was heavily criticized, especially since the population of London at the time was more than twice that of Delhi.
The married couple wrote the book out of concern that we are facing mass starvation, especially in developing countries, but also in countries such as America, where people have begun to notice the impact they are having on the environment.
Their work is credited - or blamed, depending on your point of view - for starting many of the current jitters about overpopulation.
Of course, discussions about how many people there should be have never been purely academic in nature.
They were occasionally misused to justify persecution, ethnic cleansing and genocide.
In each of these cases, the perpetrators were determined to depopulate a specific group of people, such as a particular social class, religion, or ethnic group - rather than humanity as a whole - but they are still sometimes seen as examples of the dangers that the concept of overpopulation can pose.
As early as 1834, only three and a half decades after the publication of Malthus's essay, the English poor laws were abolished and replaced by stricter ones.
This was partly due to Maltrus' concern that this social class (which he called "peasants") was proliferating too much and resulting in orphaned children being pushed into dark, unsanitary workhouses such as those described in Charles Dickens' novel Oliver Twist ".
In the following centuries, eugenics was constantly disguised as population control - or gained movement support - as during the forced sterilization of people from minority ethnic groups in America in the XNUMXs.
It was also used to limit individual freedoms.
In 1980, China introduced the controversial one-child policy, which was widely perceived as an invasive violation of the population's sexual and reproductive rights.
A conflicting future
As a result of this conflicting history, population engineering is a highly polarized field.
Today, any policy involving quotas or targets to increase or decrease the human population is almost universally condemned, except by a handful of extremist organizations.
The risk that these initiatives lead to coercion or other atrocities is considered high.
But there is little agreement beyond this.
At one end of the spectrum are those who perceive the lower fertility rate in some areas as a crisis.
One demographer was so concerned about the localized decline in the UK birthrate that he proposed taxing the childless.
As of 2019, an average of 1,65 children were born per woman in the country.
This is below the "replacement level" - the number of births necessary to maintain the same population size - of 2,075, although the population in aggregate has continued to grow due to migration from other countries.
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It is a contradictory view that slowing down and finally stopping the growth of the planet's population is not only eminently sustainable and desirable, but can be achieved exclusively by voluntary means - such as simply providing contraception to those who want it and educating women.
In this way, the advocates of this position believe that we can not only benefit from it as an entire planet, but also that we can improve the quality of life lived by the world's poorest citizens.
One organization that believes in this approach is the British charity Population Matters, which campaigns to achieve a sustainable global population.
She advocates dealing with the pressures of consumerism - especially in the developed world - on the planet, while highlighting the role that population size plays in this.
To that end, they are calling on people to take personal responsibility for the environmental crisis, in addition to working to end global poverty and inequality through debt relief and foreign aid.
"We condemn any form of population control or coercion, limiting choice," says Director Robin Maynard.
"The essence, therefore, is in enabling access, providing choice and using rights. And that's actually the most effective way for people to make decisions that are good for them and good, ultimately, for the entire planet."
On the other hand, others argue for shifting the emphasis from adjusting the number of people on the planet, however softly or indirectly this is achieved, to our activities.
Followers of this approach argue that the amount of resources each person consumes reflects more on our collective impact and point out that consumption is significantly higher in wealthier countries with lower birth rates.
Reducing our individual demands on the planet could reduce humanity's footprint without impeding population growth in poorer countries.
Moreover, the West's interest in curbing population growth in underdeveloped parts of the world has been accused of having racist overtones, especially when one considers that Europe and North America are more densely populated overall.
And finally, there is the fatalistic "solution" to the eternal population question: simply do nothing.
This attitude depends solely on the extremely unstable dynamics of our global population - it will increase significantly, but then decrease.
Each camp could get what they want in the end, though not forever.
Estimates vary, but we are expected to reach "peak humanity" around 2070 or 2080, when there will be between 9,4 billion and 10,4 billion people on the planet.
It may be a slow process - if we reach 10,4 billion, the UN expects the population to stay at that level for two decades, but eventually after that the population is projected to start declining.
In the book "Empty Planet: The Shock of Global Population Decline", the authors present a very different vision of the future than the one we are used to, in which the world is struggling with new challenges and opportunities that depopulation can bring.
In the midst of all this controversy and uncertainty, it is sometimes difficult for a person to know what to think.
Here's how the number of people on the planet could affect several key aspects of our lives in the future - the environment, the economy and our collective well-being.
Environmental challenge
The camera makes its way through the forest in Madagascar, with sweeping shots shot handheld.
Dense trees present an exciting mystery of the unknown wilderness.
And then, suddenly, there it is: a white blob jumps across the frame and into the distance.
The animal is a sifaka - a shy and elusive lemur with long limbs, pale fur and a black face, like some kind of spiky teddy bear.
This brief encounter is part of the BBC's Indian Ocean documentary with Simon Reeve, and the presenter soon reveals a startling footnote to the team's lucky discovery.
It's no wilderness at all - it's the Berenti Reserve in southern Madagascar, a tiny patch of forest surrounded on all sides by commercial plantations, and one of the last remaining places this rare creature calls home.
At the visitor center, Reeve says he is reliably informed that almost all wildlife cameramen in the area set up their equipment in the very location where the lemurs are most abundant, pointing it toward the forest to avoid buildings.
And while viewers might think they're getting a rare glimpse into an unknown wilderness, it could be argued that they're actually being served a carefully crafted illusion of untamed nature.
The documentary debunks the "wilderness myth" - the misunderstanding that can arise when people watch magnificent footage of the natural world that excludes humans entirely or drastically diminishes our omnipresence, suggesting that there are still endless stretches of untouched land.
Satellite images are a particularly powerful tool for spreading the word: from the air, it's easy to see that many countries are extremely adapted to human use.
As far as the eye can see, the country is a patch of farmland, criss-crossed by roads and rows upon rows of buildings.
Some landscapes have been so transformed in just a few decades, through engineering works or deforestation, that they are barely recognizable.
These changes come with staggering statistics.
According to the Food and Agriculture Organization of the United Nations (FAO), 38 percent of the planet's land area is used to grow food and other products (such as fuel) for people or their livestock - a total of five billion hectares.
And although our ancestors lived among the giants hunting mammoths, mega-wombats and 450-kilogram elephant birds, today we are the dominant vertebrate species on land - a group that includes everything from lizards to lemurs.
By weight, humans make up 32 percent of terrestrial vertebrates, while wild animals make up a total of only one percent.
The rest is cattle.
Wildlife conservation charity the World Wide Fund for Nature found that wildlife numbers fell by two-thirds between 1970 and 2020 - the same period the global human population more than doubled.
Moreover, as our dominance grows, many environmental changes are occurring in parallel - and a number of prominent environmentalists, from primatologist Jane Goodall, of chimpanzee fame, to naturalist and TV presenter Chris Peckham, have expressed concern.
In 2013, Sir David Attenborough explained his own view in an interview with the Radio Times:
"All our environmental problems are becoming easier to solve with fewer people and harder - eventually even impossible - to solve with more and more people."
Concerns about humanity's ecological footprint have led some people to decide to have fewer children themselves - including the Duke and Duchess of Sussex, who announced in 2019 that they would have no more than two for the sake of the planet.
In the same year, Miley Cyrus announced that she would not have children yet because the earth was "angry".
An increasing number of women are joining the anti-natalist movement and entering the "birth strike", until the current climate crisis and the extinction crisis are not resolved.
The trend was fueled by a 2017 study which calculated that having one less child in the developed world could simply reduce a person's annual carbon emissions by 58,6 tonnes of "carbon dioxide equivalent" or CO2e - more than 24 times the savings of when you don't have a car.
One 2019 study, led by Jennifer Šjuba, associate professor of international studies at Rhodes College in Tennessee, analyzed population growth levels in more than 1.000 regions in 22 European countries between 1990 and 2006, and compared them with how patterns of urban land use and carbon dioxide emissions changed in the same period.
The team concluded that the sheer number of people has a "significant influence" on these environmental parameters in Western Europe, but that these are not the most important factors in Eastern Europe.
This multi-layered report, which advocates the idea that population growth leads to ecological degradation, has been supported by many other studies - but also by the impact of increasing demand for natural resources, especially in wealthier countries.
Moreover, many environmentalists now believe that many of the problems we currently face are largely caused by consumption rather than overpopulation—from that point of view, concerns about the latter unfairly place the blame on poorer countries.
A 2021 study showed that in the US the environment is being degraded by both population growth and the use of non-renewable energy sources, while another showed that economic development and the use of natural resources in China from 1980 to 2017 led to higher carbon dioxide emissions .
To make matters more intriguing, other research has shown that while the depletion of natural resources and urbanization in China have increased the rate of environmental destruction, they have been partially mitigated by the availability of "human capital"—the practical knowledge and skills of the human population.
Today, it is widely accepted that humans are putting unsustainable pressure on the world's limited resources - a phenomenon highlighted by "Earth Environmental Debt Day", the date each year when humanity is estimated to have used up all the biological resources that the planet can sustainably replenish.
In 2010, that date fell to August 8. This year it was July 28.
Whether the problem is too many people, the resources we use up, or both, "I can't understand how more people can be good for the environment," says Šjuba, who wrote the book 8 billion and growing: How sex, death and migration shape our world.
She suggests that one way to resolve this issue might be to view people and the environment as one entity, "but man, that's a really tough argument," she says.
However, Šjuba especially points out that the idea of an impending "population bomb" that is coming to destroy the planet, as suggested by the Ehrlichs' book, is outdated.
"At the time that book was written, I think there were 127 countries in the world where women had an average of five or more children in their lifetime," she says.
In that era, population trends really seemed to be exponential - and she suggests that this instilled in some generations a panic about population growth that is still alive today.
"But today you have only eight countries with a fertility rate above five," Šjuba says.
"And that's why I think it's important to understand that those trends have changed."
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Economic opportunities
In 2012, Singapore's government came up with an unusual way for citizens to celebrate the country's independence - and conveyed important instructions via a new rap song.
The hit aimed to encourage young people to have more children and mixed colorful allusions with patriotic references to the culture and landscapes the country has to offer.
"...Let's make a little man that looks like you and me, I'm exploring your body like a night safari, I'm a patriotic husband and you're a patriotic wife, Let me enter your camp and create a life...", read part of the lyrics of the song.
It was carried out amid fears over Singapore's extremely low birth rate, which stood at just 1,1 births per woman as of 2020.
It is an extreme example of what has become a common trend in rich countries, where people marry later and choose to have fewer children.
In Singapore, this has raised concerns about possible consequences for the country's economy, prompting the government to call on citizens to do their duty.
It's a key concept in economics: the more people you have, the more goods or services they can produce and the more they can consume - so population growth is economic growth's best friend.
This is one of the reasons why concerns about population growth in developing countries are sometimes seen as problematic - many developed countries are already densely populated, which is part of the reason they have become rich.
Denying other countries these opportunities is seen as unfair or even racist.
However, slower population growth does not always follow economic decline.
Take for example Japan, which anticipated the global trends of rich countries and achieved a birth rate below the level of renewal as early as 1966, when it suddenly fell from about two to 1,6.
"I don't think we have a case here that the Japanese economy has fallen to the extent that people represent, if you look at their standard of living," said Andrew Mason, professor emeritus in the University of Hawaii's Department of Economics.
"They have invested a lot in human capital - so they have fewer children, but they have put an emphasis on education and they have very good health care systems."
Mason also points out that saving and investing are common in Japan:
"So there was an increase in monetary capital and higher productivity. If you put those things together... I think Japan is a good case study of why we shouldn't panic about falling birth rates."
And there are other ways to ensure the economic growth of the country.
Mason points out that immigration often provides a useful source of new workers, and this is achieved without adding new people to the total population.
But immigration remains a controversial and highly politicized topic in many countries, so without a societal change in how it is perceived, some countries will not have this option.
"Just think of countries like Japan and South Korea, where historically there's been a lot of resistance to immigration, they're going to find more and more that it's to their advantage to change that policy," Mason says.
Likewise, the benefits that immigration can provide are inherently extremely unequal - one country gets a boost to its economy at the cost of another whose workers have left.
There is an increasingly pronounced feeling that the global obsession with chasing economic growth at any cost is outdated and should be completely abandoned.
"One of the things that frustrates me about the overpopulation debate is that most of the comments come from the mouths of the same people - that we don't want too many people, but also that we want our economy to be constantly growing," Šjuba says.
"In a world where there are fewer and fewer people, we really need to completely discard the mindset that growth equals progress," she says.
A happier future
However, demography does not only affect the environment and the economy - it is also a powerful invisible force that affects the quality of life of people around the world.
According to Alex Ezeh, a professor of global health at Drexel University in Pennsylvania, the total number of people in a country is not the most important factor.
Instead, the rate of growth or decline of its population is key to its future prospects - it determines how quickly things change.
Take Africa for example, where Ezeh explains that there are currently radically different rates of population growth, depending on where you look.
"In many countries, particularly in southern Africa [one of the five regions defined by the United Nations], the birth rate has actually fallen and the use of contraceptives is on the rise - the rate of population growth is slowing down, which is good news in some cases," says Ezek.
At the same time, some countries in Central Africa still have a high rate of population growth, as a result of high birth rates and longer life expectancy.
In some places, it's well over 2,5 percent a year, "which is a huge number," Ezeh says.
"The population will double every 20-plus years in a large number of countries."
Even within one region, different countries can be on surprisingly different trajectories - Ezeh cites the example of East African neighbors Burundi and Rwanda.
Although the former still has a high growth rate - at 5,3 births per woman - the latter is slowing down, with 3,9 births per woman in 2020 compared to 4,5 in 2010.
"I think the discussion about size and numbers is completely beside the point," says Ezeh.
"Imagine a city that doubles in size every 10 years - and that happens to a lot of cities in Africa - what government will actually have the resources to improve the current infrastructure every 10 years, to maintain the right level of satisfaction of all those services."
Ezeh explains that in particular, it is very difficult to support the development of human capital in conditions of extreme growth - which research has shown plays an important role in the happiness of people in cities, even more than the amount of money they earn.
It is also considered to be an important predictor of economic growth, in addition to the mere number of people in a country.
"When economists think about it, large populations are good for many different outcomes, but do you achieve that large population in 10, 100, or 1.000 years? The more time you take to achieve that, the more you're able to put the right structures in the system to support that population," says Ezeh.
One factor with a well-documented role in slowing this growth rate is the education of women, which has the side effect of increasing the average age at which they give birth.
"Over time, women gain access to education, they have positions outside the family, jobs, everything that competes with having children," says Ezeh.
However, Ezeh particularly emphasizes the value of education regardless of its impact on the size of the population - it is one of the 17 Sustainable Development Goals of the United Nations.
And that goes to the very essence of a modern view of population engineering - the policy should be implemented for the benefit of society, and if it happens to lead to beneficial demographic changes, that's just a bonus.
"I think one of the things we don't want to do is instrumentalize women's education and make it look like we want them to go to school just because we want women to have fewer children ... there are a lot of positives there that we don't want to minimize by thinking about it in context of declining fertility," says Ezeh.
Moreover, the consequential side effects of policies implemented for other reasons highlight the harsh reality of population science - how imprecise its predictions often are.
Across the planet, decisions made by governments over the coming decades will have a huge impact on how many people will be on the planet - having the power to shift us from a future of 10 billion people to one of 15 billion, or vice versa.
"I think one of the things we know for sure is that when people say that the population in Africa is projected to be so-and-so in such-and-such a year, it's not meant to be," Ezeh says.
"If you look at the Southern African region ... its population could be three to four times what it is today by 2100, but it could also be less than 50 percent smaller than what it is today by 2100. That's a very wide range of possibilities - either to make the necessary investments to achieve a growth rate consistent with where countries want to go. So that's the breadth of possibilities that exist."
Increasing presence
However, while the extent to which humanity will continue to expand on the planet has yet to be decided, some paths have already been charted.
And one is that the human population will most likely continue to grow for some time, regardless of any attempt to reduce it.
This future boils down to a phenomenon known as the "demographic flywheel," in which a young population with a below-replacement fertility rate will continue to grow as long as death rates and migration remain the same.
This is because the change in the population does not depend only on the birth rate - the structure of the population also has an impact, especially the total number of women of childbearing age.
All this means that in countries where the fertility rate is high, the full impact of this increase is not felt until women in that population reach reproductive age decades later.
A 2014 study showed that, even in the event of a major global tragedy such as a pandemic or a catastrophic world war, or a draconian one-child policy implemented in every country in the world—which, of course, no one hopes—our population and further grow to 10 billion by 2100.
Even after a massive catastrophe in which two billion people would die in a five-year period in the middle of the century, the population would still grow to 8,5 billion people by 2100.
Whatever happens, the authors conclude, there will still be many, many people around us at least until the next century.
With humanity likely to become even more dominant in the coming years, finding ways to live together and protect the environment could be our species' greatest challenge yet.
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