Alarming study predicts date when half of humanity could disappear

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A mathematical model from an unexpected domain

This is not a disaster movie scenario. This is not the pitch for a dystopian series on Netflix either. It’s a scientific study published in a peer-reviewed journal, carried out by serious researchers, and its conclusions are enough to give you a cold sweat.

Recently, a team of scientists decided to apply a very particular mathematical tool to the study of world demographics. A tool which, originally, had absolutely nothing to do with human beings. It was used to understand the behavior of glasses and amorphous materials in physics.

By crossing this tool with demographic data covering more than 12,000 years of human history, they obtained results that stuck perfectly to the past. But it was when they pointed their model towards the future that things got really worrying.

Their conclusion? In a very specific scenario, the world population could be halved. And not in centuries or millennia. Much sooner than anyone would have imagined. The brought forward date made the entire scientific community shudder.

When numbers tell a story no one wants to hear

To understand the scope of this study, we must first review what we know about world demography. And above all, on what we think we know. Because for decades we lived in a comfortable illusion.

At the start of the 20th century, the Earth had approximately 1.6 billion inhabitants. A century later, there were more than 6 billion of us. In November 2022, the symbolic milestone of 8 billion was crossed. A demographic explosion without precedent in the history of our species.

This dazzling growth gave birth to a diffuse but tenacious feeling: that humanity would never stop growing. That the curve could only go upwards. That the world of tomorrow would always be more populated than that of today.

But demographers knew that this vision was misleading. Since the 1970s, a discreet but massive phenomenon was occurring before our eyes. The global fertility rate had begun to fall, slowly but surely.

The time bomb that no one saw coming

In the 1960s, the average woman had five children in her lifetime, globally. Today, this figure has fallen to around 2.3. In many developed countries, it has even fallen below the replacement threshold of 2.1 children per woman.

Japan, South Korea, Italy, Spain, Germany… These countries have been facing accelerated aging of their populations for years. Maternity centers are closing, schools are emptying, and retirement homes are overflowing.

In South Korea, the fertility rate reached a dizzying figure of 0.72 children per woman in 2023. A world record. At this rate, South Korea’s population could be cut in half by the end of the century, without even needing a catastrophe.

But this phenomenon is no longer limited to rich countries. China, long a symbol of global overpopulation, saw its population decline for the first time in 2022. India overtook it as the world’s most populous country. And even in sub-Saharan Africa, the last bastion of high birth rates, rates are starting to decline.

A tool borrowed from the physics of materials

It is in this context of growing demographic uncertainty that the study in question was published. And his approach is original to say the least. Because the researchers did not start from a classic demographic model.

They used a nonlinear differential equation, initially designed to describe the behavior of glasses and amorphous materials. In physics, these materials have fascinating properties: they are neither completely solid nor completely liquid. Their structure is disordered, unpredictable.

The researchers’ idea was audacious: what if the dynamics of human populations resembled, mathematically, those of these chaotic materials? What if the same equations could describe both phenomena?

This intuition may seem far-fetched at first. But in science, bridges between disciplines have often led to the most important discoveries. Chaos theory itself was born from the meeting between meteorology and pure mathematics.

12,000 years of history scrutinized

To test their hypothesis, the researchers compared their equation with empirical demographic data covering an immense period: from the Neolithic to the present day. That’s about 12,000 years of human history.

In the Neolithic, humanity numbered a few million individuals at most. Growth was extremely slow, punctuated by climatic hazards, famines and epidemics. It took millennia for the world population to reach the first billion, around 1800.

Then came the industrial revolution. In the space of two centuries, the population exploded, from 1 to 8 billion. Advances in medicine, agriculture and sanitation have reduced infant mortality and increased life expectancy dramatically.

Researchers have called this phase of exponential growth “compressed.” A brutal, almost violent acceleration of the demographic curve. An outburst that humanity had never experienced before.

Le moment où la courbe a commencé à fléchir

But their model also captured another phenomenon, more recent and more subtle. Since around 1970, global population growth has entered a new regime. Researchers call it “stretched” exponential growth.

Concretely, the population continues to increase, but more and more slowly. The annual growth rate, which exceeded 2% in the 1960s, has fallen below 1% today. And it continues to decline.

This slowdown is the direct consequence of falling fertility rates globally. The more societies develop economically, the more women have access to education and contraception, and the fewer children they have. This is a trend observed everywhere, without exception.

The researchers’ mathematical model reproduced this transition with remarkable precision. The shift from “compressed” to “stretched” growth was exactly consistent with historical data. The equation worked. Perfectly.

The terrifying prophecy of 1960

Before going further into the results of this study, we must take a detour to the year 1960. Because that year, an Austrian physicist named Heinz von Foerster published an article that would mark minds for decades.

Von Foerster and his collaborators had carried out a mathematical extrapolation of global population growth. Their conclusion was astounding: if the current trend continued, the world population would diverge towards infinity around 2026.

Yes, you read that right. Infinity. In other words, a mathematical singularity where the numbers no longer have any meaning. A demographic “Doomsday,” as the press of the time nicknamed it. The article was also published in the journal Science under a provocative title.

Obviously, this prediction did not come true. Humanity has escaped this catastrophic trajectory thanks to the global decline in fertility rates. But von Foerster’s prophecy had the merit of asking a fundamental question: how far can demographic growth go?

The specter of Malthus still looms

Von Foerster was not the first to question the limits of human growth. Long before him, an English pastor named Thomas Robert Malthus had theorized, as early as 1798, that the human population was growing faster than available resources.

According to Malthus, this divergence could only lead to catastrophes: famines, wars, epidemics. “Natural fixes” that would bring the population back to a sustainable level. A dark vision, which has been widely criticized since, but which has never been completely refuted.

In the 20th century, the biologist Paul Ehrlich took up the Malthusian torch with his shocking book “The Population Bomb”, published in 1968. He predicted massive famines in the 1970s and 1980s, which would kill hundreds of millions of people.

These famines did not occur, thanks to the green revolution and the progress of industrial agriculture. But the debate over the limits of Earth’s carrying capacity has never stopped. It has even become more urgent than ever, in times of climate change.

Load capacity: the key concept that everyone ignores

Carrying capacity is a fundamental concept in ecology. It designates the maximum number of individuals of a species that a given environment can sustainably support, taking into account available resources.

For wild animals, this concept is relatively simple to apply. A forest can only support a certain number of deer. An ocean can only support a certain number of whales. When the population exceeds carrying capacity, it collapses.

For humans, it’s much more complicated. Because we have the capacity to modify our environment, to create new technologies, to find new sources of food. The green revolution of the 1960s is the most striking example.

But this ability to adapt has its limits. Arable land is not infinite. Neither does fresh water. And climate change threatens to drastically reduce agricultural yields in many regions of the world. The question of the Earth’s carrying capacity is therefore far from theoretical.

Alarm signals are multiplying

In recent years, there have been increasing signs of a world approaching its limits. And they come from very different directions, which makes the picture all the more worrying.

In terms of climate, heat records are falling one after the other. The year 2023 was the hottest on record. Extreme weather events – heatwaves, floods, droughts – have become the norm rather than the exception.

On the biodiversity side, the situation is just as alarming. According to the WWF, wild vertebrate populations have declined by an average of 69% since 1970. Pollinating insects are disappearing at a worrying rate, directly threatening our ability to produce food.

In terms of resources, groundwater is depleting in many regions of the world. India, the Middle East, the Mediterranean basin… Hundreds of millions of people face increasing water stress. And the demand continues to increase.

When science fiction becomes a plausible scenario

It is exactly this type of convergence of crises that the study’s researchers wanted to model. Not to predict the future with certainty, but to understand what might happen if things go wrong. Really bad.

Their question was simple but dizzying: what would happen if major environmental crises suddenly imposed severe limits on the Earth’s carrying capacity? What if several disasters struck at the same time, creating an unstoppable domino effect?

This type of scenario has a name in the scientific literature: “polycrisis”. A term popularized in recent years to describe the convergence of multiple interconnected crises – climatic, health, geopolitical, economic – which reinforce each other.

Historian Adam Tooze, professor at Columbia University, largely contributed to popularizing this concept. According to him, we already live in a world of polycrises. Covid-19, the war in Ukraine, the energy crisis, global inflation… So many shocks which, taken individually, are manageable, but which, combined, can become devastating.

The historical precedent that sends shivers down your spine

The idea of ​​a brutal demographic collapse is not a pure theoretical abstraction. Human history is replete with examples of populations collapsing in record time, often in completely unexpected ways.

The most famous example is undoubtedly that of the Black Death, in the 14th century. Between 1347 and 1353, this pandemic killed between 30 and 60% of the European population. Some cities lost three quarters of their inhabitants in a few months.

More recently, the Spanish flu of 1918-1919 caused between 50 and 100 million deaths in less than two years, in a world which had only 1.8 billion inhabitants. Compared to the current population, a similar event could cause hundreds of millions of victims.

And let’s not forget more localized civilizational collapses. The Roman Empire, the Mayan civilization, Easter Island… So many societies which seemed invincible and which collapsed, often under the weight of the overexploitation of their natural resources.

The shadow of Covid-19 on researchers’ calculations

The study was carried out in a post-pandemic context which gives its conclusions particular resonance. Covid-19 reminded the whole world how fragile our civilization could be in the face of a microscopic pathogen.

Within weeks, global economies came to a halt. Supply chains have broken. Hospitals were submerged. And millions of people died, despite considerable progress in modern medicine.

The official Covid-19 death toll exceeds 7 million, but excess mortality estimates suggest a much higher figure, possibly higher than 20 million. And this, for a virus whose fatality rate was relatively moderate.

What would happen in the face of a deadlier pandemic? Virologists have been warning for years that the risk of a pandemic caused by a virus that is both highly contagious and very lethal is far from negligible. H5N1 avian flu, for example, is under close surveillance.

Conflicts: the other factor that researchers have integrated

The pandemic is not the only risk factor modeled by researchers. Armed conflicts also feature in their disaster scenario. And recent news shows that this threat is far from theoretical.

The war in Ukraine, which began in February 2022, reminded the world that major conflicts between nuclear powers were not a relic of the past. Tensions between the United States and China over Taiwan add an additional layer of geopolitical uncertainty.

A nuclear conflict, even limited, would have catastrophic demographic consequences. Beyond the direct victims, a “nuclear winter” could drastically reduce global agricultural production for years, causing large-scale famines.

Researchers at Rutgers University estimated in 2022 that a nuclear conflict between the United States and Russia could cause the deaths of more than 5 billion people in two years, mainly because of the global famine that would ensue. A number that makes you dizzy.

The water crisis: the silent detonator

Among all the factors likely to cause a sudden drop in the Earth’s carrying capacity, there is one that is often underestimated: water. Because without fresh water, there is no agriculture, no industry, no human life.

However, the water crisis is already a reality in many regions of the world. Lake Chad, in Africa, has lost 90% of its surface area since the 1960s. The Aral Sea, in Central Asia, has almost disappeared. The Colorado River in the United States no longer reaches the sea in certain years.

In India, where more than 1.4 billion people live, groundwater is being depleted at an alarming rate. Entire cities, like Chennai, have already experienced major water crises, with taps running dry for weeks.

Climate change is only making this situation worse. The glaciers of the Himalayas, which supply fresh water to much of Asia, are melting at an accelerating rate. According to some estimates, they could lose a third of their volume by 2100.

World power on a wire

The question of water is closely linked to that of food. Because agriculture represents around 70% of global fresh water consumption. Without water, no crops. Without crops, no food. The equation is terrifyingly simple.

Today, around 735 million people in the world suffer from hunger, according to the FAO. This figure has been increasing for several years, after decades of progress. The Covid-19 pandemic, the war in Ukraine and extreme weather events have reversed the trend.

Agricultural yields, which had exploded thanks to the green revolution, are starting to plateau in many regions. Soils are becoming exhausted, pesticides are losing their effectiveness, and high-yielding crop varieties are showing their limits in the face of climate change.

Some experts estimate that the Earth could theoretically feed 10 to 12 billion people, provided we radically transform our food systems. But others are much more pessimistic and believe that we have already exceeded the sustainable carrying capacity of the planet.

The figure of 2 billion that changes everything

This is where the study takes on its full dimension. Because the researchers were not content to show that their model worked for the past. They wanted to explore what would happen in extreme scenarios. And the scenario they chose is particularly striking.

They modeled what would happen if Earth’s sustainable carrying capacity dropped suddenly. Not gradually, over decades. Brutally. As if under the effect of a sudden shock. A cascade of crises which, in a few years, would drastically reduce the planet’s capacity to support human life.

The figure they used as a working hypothesis is striking: around 2 billion people. That is, the carrying capacity that the Earth could have if major crises – climate collapse, pandemics, conflicts, resource shortages – hit simultaneously.

To put this figure into perspective, 2 billion is approximately the world population in 1927. It is a quarter of the current population. Returning to this level would mean losing 6 billion human beings. A truly inconceivable figure.

L’équation qui a tout révélé

It is by injecting this hypothesis into their non-linear differential equation that the researchers obtained the result that makes one tremble. A result that the main author of the study, Alessio Zaccone, took care to contextualize with the greatest caution.

The equation showed that, in this extreme scenario, the demographic decline would not be gradual. He would be brutal. Fast. Devastating. The population curve, instead of gently declining, would plunge like a stone.

And the speed of this collapse is what most surprised the researchers themselves. Because the model does not predict a decline spread over centuries. He predicts collapse in just a few decades. Maybe even less.

But when exactly? This is the question everyone is asking. And the answer, contained in the results of the study, is closer than you think. Much closer.

A researcher with an atypical background

Before revealing the date given by the researchers, it is important to understand who is behind this study. Because the credibility of a scientific result also depends on that of its authors.

Alessio Zaccone, the lead author, is not a trained demographer. He is a theoretical physicist, specializing in the physics of condensed matter and disordered materials. Exactly the domain from which the equation used in the study comes.

This atypical profile is both a strength and a weakness. A strength, because it brings a fresh perspective and new mathematical tools to a field that needs them. A weakness, because traditional demographers could be tempted to brush aside its conclusions.

But the study was published in the journal Chaos, Solitons & Fractalsa recognized, peer-reviewed scientific publication. Which means it has been peer reviewed and validated before publication. A guarantee of seriousness that cannot be ignored.

The scientist’s caution in the face of the power of the result

Alessio Zaccone himself insisted on putting very clear safeguards around his conclusions. And his carefully chosen words speak volumes about the tension between scientific rigor and the potentially explosive scope of his results.

The researcher particularly insisted on the fact that the reference scenario, the one which corresponds to current trends, “does not produce a catastrophic singularity”. In other words, if nothing changes suddenly, the world population should continue to evolve in a relatively stable manner.

This is a crucial point. The disaster scenario is not the most likely scenario according to the researchers themselves. This is an “illustrative mathematical scenario”, designed to show how population dynamics are sensitive to shocks.

But this caution should not mask the essential: the model shows that the collapse is possible. Not certain, not likely, but possible. And it’s this possibility, supported by solid mathematics, that makes the study so troubling.

The parameter that tilts the destiny of humanity

At the heart of the model is a key parameter that researchers call the “determining parameter.” It is this which decides whether the world’s population stabilizes, grows or collapses. A simple number in an equation, on which the fate of billions of human beings depends.

In the reference scenario, this parameter “remains in a stabilizing regime”, as Zaccone explained. The population continues to grow, but more and more slowly, before stabilizing and then, eventually, gently declining.

But if major crises were to suddenly modify this parameter – by reducing the carrying capacity of the Earth in a sudden manner – then the stabilizing regime would give way to a regime of collapse. And the transition could be extremely rapid.

This is what we call in mathematics a “bifurcation point”. A critical moment when a system switches from one state to another in an irreversible manner. Like a marble rolling to the top of a hill: a slight gust of wind, and it rolls down the slope with no possible return.

Was the United Nations right?

The findings of this study resonate with other work carried out by leading institutions. United Nations population projections, for example, predict a peak in global population of around 10.4 billion in the 2080s, followed by a gradual decline.

But some demographers consider these projections too optimistic. A study from the Institute for Health Metrics and Evaluation (IHME), published in The Lancet in 2020, estimated that the world population could peak much earlier, around 9.7 billion in 2064, before declining.

2064. The same date that recurs in the study we describe here, but in a radically different context. The United Nations speaks of a gradual and manageable decline. The researchers in this study speak of a scenario of sudden collapse.

The difference between the two scenarios is dizzying. On the one hand, a soft landing. On the other, a crash. And it is the nature of the shocks that our civilization will undergo in the coming decades which will determine which of these two scenarios will come true.

The crucial role of climate change

Among all the factors likely to precipitate a demographic collapse, climate change occupies a central place. Because it acts as a threat multiplier, simultaneously aggravating the food, water, health and geopolitical crises.

The IPCC (Intergovernmental Panel on Climate Change) has repeatedly warned that global warming could make some regions of the world literally uninhabitable by the end of the century. Southern Asia, the Middle East and North Africa are particularly threatened.

Temperatures regularly exceeding 50°C, combined with high humidity, could create “wet bulb” conditions that are deadly to humans. Beyond a certain threshold, the human body can no longer cool itself by perspiration, even in the shade. Death occurs within a few hours.

These extreme conditions could force hundreds of millions of people to migrate, creating unprecedented geopolitical tensions. And these mass migrations, in turn, could trigger conflicts over access to resources in host regions.

The collapse of biodiversity: the invisible factor

There is another factor that traditional demographic models often underestimate: the collapse of biodiversity. Because the survival of humanity depends closely on the health of the ecosystems that surround us.

Pollinating insects, for example, are responsible for pollinating around 75% of the world’s food crops. Their gradual disappearance, caused by pesticides, habitat loss and climate change, directly threatens our ability to feed ourselves.

The oceans, which provide protein to more than 3 billion people, are acidifying and warming at an alarming rate. Fish stocks are collapsing in many regions. Coral reefs, nurseries of marine life, are bleaching and dying one after the other.

If these ecosystems were to collapse synchronously – a scenario that some scientists consider plausible – the Earth’s carrying capacity would indeed drop precipitously. Exactly the type of shock modeled by the study’s researchers.

The “illustrative scenario” which may not be one

This is where the tension between scientific prudence and the urgency of the message reaches its climax. Because if the researchers insist on the “illustrative” nature of their disaster scenario, the available scientific data suggests that this scenario is not as hypothetical as one might believe.

The Global Risks Report of the World Economic Forum, published each year, regularly ranks environmental risks among the most likely and most impactful threats for the next decade. Climate change, loss of biodiversity and water crises consistently top the list.

Furthermore, the climatic tipping thresholds – those points of no return beyond which certain processes become irreversible – are getting dangerously close. The melting of the Greenland ice cap, the thawing of the Siberian permafrost, the death of the Amazon forest… Each of these shifts could trigger a chain reaction with unpredictable consequences.

As climatologist Johan Rockström, director of the Potsdam Institute for Climate Impact Research, has observed, we are “playing Russian roulette with the planet.” And each additional degree of warming adds a bullet to the barrel.

The fateful date revealed by the model

Now let’s return to the study itself. Because after having tested their model on 12,000 years of historical data, after having verified its precision and robustness, the researchers injected their shock scenario. And the result fell, cold as a blade.

According to their results, if the Earth’s sustainable carrying capacity dropped suddenly to around 2 billion people, the equation would predict a rapid global population decline. The population would potentially be reduced half of this 2064.

2064. In barely forty years. Half of humanity. That is to say around 4 billion fewer people on the planet, compared to today. A figure that beggars belief.

To put this into perspective, it’s as if the entire populations of North America, South America and Europe disappeared. Or as if the Second World War, with its 70 to 85 million deaths, was repeated fifty times in the space of a few decades.

What “halved” really means

It is important to understand what this expression actually means. Because behind the abstract figures hide terrifying human realities.

A halving of the world’s population does not necessarily mean that 4 billion people would die in spectacular disasters. The decline could take several forms: a drastic drop in the birth rate, a sudden increase in mortality, or – most likely – a combination of the two.

In the scenario modeled by the researchers, it is the “carrying capacity constraints” that come into play. Concretely, this means that the Earth could no longer feed, water and shelter as many people. Famines, epidemics, conflicts over resources would do the rest.

This is a scenario where civilization as we know it would probably not survive. Health systems would collapse. Global supply chains would cease to function. The most fragile states would fall into chaos.

The response from the scientific world

Since the publication of the study in Chaos, Solitons & Fractalsreactions in the scientific community were numerous. And they oscillate between fascination with the originality of the approach and caution regarding the interpretation of the results.

Some demographers have welcomed the use of a mathematical tool from physics to model population dynamics. This interdisciplinary approach is increasingly encouraged in the academic world, because it allows us to go beyond the limits of traditional models.

Others, however, expressed reservations. Is the scenario of a sudden drop in carrying capacity to 2 billion people realistic? Are the underlying assumptions strong enough? Can the model really capture the complexity of human demographic dynamics?

These questions are legitimate. But they should not make us forget the central message of the study: our demographic trajectory is much more fragile than we think. And the shocks that could derail it are far from improbable.

“This is not a forecastâ€

Alessio Zaccone took care to remind us forcefully: “We insist on the fact that this is not a forecast, but rather an illustrative mathematical scenario aimed at showing the sensitivity of population dynamics to abrupt environmental or societal changes. HAS”

This sentence is essential. She draws a clear line between a prediction and a warning. Researchers are not saying that the world’s population sera halved by 2064. They say it could l’être, dans un scénario extrême mais pas impossible.

The researcher added that “the current trajectory remains relatively stable and does not imply imminent collapse.” A reassuring sentence, certainly. But which contains an often neglected keyword: “imminent”. What is not imminent today could become imminent tomorrow, if crises accumulate.

The study therefore presents itself as an exploration tool, not as a crystal ball. It offers “a compact way to explore possible futures, from lasting stabilization to uncontrolled growth or sudden collapse, within a unified mathematical language.”

And now, what do we do?

The publication of this study comes at a pivotal moment in human history. The decisions we make collectively in the coming decades will determine whether the doomsday scenario remains a simple mathematical hypothesis or becomes a reality.

The energy transition, the protection of biodiversity, the sustainable management of water resources, the reform of food systems… So many titanic projects which are already underway, but whose pace is considered largely insufficient by the scientific community.

The Paris Climate Agreement, signed in 2015, aimed to limit warming to 1.5°C compared to the pre-industrial era. However, we are already at around 1.2°C of warming, and the current trajectory takes us towards 2.5 to 3°C by the end of the century.

Every tenth of a degree counts. Each year of delay in climate action reduces the room for maneuver available to humanity. And the study reminds us, with the coldness of mathematics, that the consequences of prolonged inaction could be much more serious than most people imagine.

The paradox of our time

There is something profoundly paradoxical in our situation. Never has humanity been so powerful, so connected, so technologically advanced. And yet, she has never been so vulnerable to the threats she herself created.

We have conquered space, decoded our genome, created artificial intelligence capable of beating the best chess players. But we have not succeeded in preventing the planet’s temperature from rising, species from disappearing, oceans from emptying.

This study is a stark reminder that mathematics mocks our hopes and denials. The equations don’t lie. And if the variables we provide them change suddenly, the results change too. Just as brutally.

The future is not written. But it is calculable. And the calculations these researchers have made should keep us all up at night. Not to paralyze us with fear, but to push us to act. Because if 2064 is the deadline, the time to act is now.

A warning for future generations

The children born today will be forty years old in 2064. It is their world that is at stake. It is their future that this mathematical equation attempts to describe. And it’s our responsibility to ensure that the worst-case scenario never comes true.

The study published in Chaos, Solitons & Fractals is not a prophecy of the end of the world. It is a scientific alarm signal, formulated in the rigorous language of mathematics, which tells us: be careful, the system is more fragile than you think.

And this signal deserves to be heard. Not to fall into despair, but to understand the urgency of the situation. Because between lasting stabilization and sudden collapse, the difference may only come down to a few decisions taken in the coming years.

Political, economic, technological and, above all, collective decisions. Decisions that will determine whether the global population curve lands softly or crashes into the ground. The equation is established. It’s up to us to write the solution.