Synthesizing findings from hundreds of recent peer-reviewed scientific studies, a comprehensive new article reviews the effects of expanding human populations on humanity’s most pressing environmental problems.
by Alon Tal
A vast amount of research and rhetoric is devoted to the world’s many sustainability challenges. Yet most advocates and scientists assiduously avoid acknowledging the predominant driver of today’s key environmental problems: overpopulation.
Years ago, sustainable population was recognized as central to the global ecological agenda. But over time, too many green leaders became loathe to address the topic. It is rarely taught in universities. Environmental agencies remain completely obtuse. But the problem has not gone away. On the contrary, environmental damage functions are rarely linear, so the consequences of population pressures are more severe than ever.
That’s why I authored a comprehensive review of the subject in the academic journal Encyclopedia: The Environmental Impacts of Overpopulation.
The article surveys recent scientific literature on the six most pressing environmental crises facing humanity: deforestation, climate change, biodiversity loss, fishery depletion, water scarcity, and desertification. Drawing on hundreds of peer-reviewed studies, one conclusion becomes crystal clear: unless the world confronts overpopulation, genuine environmental progress will remain elusive.
Here’s a brief summary of what emerges about each of these global challenges.
1. Deforestation: Trees Fall as Populations Rise
Global deforestation remains staggering, especially in tropical regions. Between 2001 and 2023, Brazil lost nearly 69 million hectares of forest, while Indonesia lost over 30 million. Most of this destruction wasn’t for lumber exports or furniture—it was simply to make room for 34 million and 59 million more people respectively.
One alarming but unfortunately typical example involves the Democratic Republic of the Congo (DRC). Despite being home to one of the planet’s largest carbon sinks, the DRC has lost millions of hectares of forest in just two decades.
Why?
Well, the country’s population doubled during this period and is now a staggering 111 million. With only 20% of Congolese having access to electricity, an increasing number of households rely on wood for cooking and heating. Similarly, in Malawi, a 1% increase in population is associated with a 2.7% rise in deforestation. As population swells, communities destroy their forests simply to survive.
2. Climate Change: More People, More Carbon Emissions
Every person is born with a carbon footprint. That means more people equals more greenhouse gas emissions. Even in countries with low per capita emissions, the cumulative impact of rising populations is massive. And it increases every day. It is no surprise that historically, global population and greenhouse gas emissions are so closely linked.
Take Israel as an example. Over the past decade, it has made impressive strides in reducing per capita emissions to meet its climate targets. But with an annual population growth of around 2%, the country’s total emissions are still set to double—even as individual emissions rates decline. Population growth steadily erases the hard-earned gains from green technologies and behavioral change.
A landmark 2017 study from the University of British Columbia building on earlier research found that having “one fewer child” was nearly 50 times more effective at reducing carbon emissions than lifestyle changes like going vegan or giving up flying.
3. Biodiversity Loss: More People – Less Nature
The World Wildlife Fund’s 2024 Living Planet Report reported a 73% decline in the earth’s monitored vertebrate populations between 1970 and 2020. The magnitude of such damage is hard to imagine. While habitat fragmentation, overhunting, and pollution are often cited as culprits, each of these pathologies ultimately is associated with population growth.
In Madagascar, population surged from 4 million in 1950 to 32 million in 2024. During this time, the island lost about 80% of its unique forests. Species found nowhere else on Earth—including the inimitable lemurs and rare frogs—are quickly vanishing.
Haiti tells a similar story. Its population grew from 3.2 million in 1950 to over 11 million today. Forest cover plummeted from 50% to just 1%, leading to a collapse of many endemic species.
4. Overfishing: Oceans Can No Longer Keep Up
The global appetite for fish has skyrocketed, with demand expected to double again by mid-century. Once-abundant fish stocks are now dangerously depleted: The UN reported in 2024 that the percentage of stocks fished at unsustainable levels nearly quadrupled globally during the past three decades. Yes, technology makes fishing more efficient. But the drop is largely because more people want more seafood.
In Senegal, where the population doubled from 9 million in 2000 to 18 million in 2023, overfishing has caused stocks to collapse. The Philippines offers another cautionary tale. With 55% population growth in the first quarter of the 21st century, local fisheries are under enormous pressure. In the South China Sea, stocks have declined by more than 70% since the 1960s.
5. Water Scarcity: Shrinking aquifers and thirsty cities
Global domestic water demand has increased six-fold since 1970. Much of this is driven by population growth. Jordan offers a sobering example. With a population that increased twenty-fold since 1948, this dryland country is among the world’s most water-scarce. Urban households receive water only once a week, and farmers routinely tap illegal pipelines just to keep crops alive. The ancient Disi aquifer is being “mined “ to keep up with the country’s mounting requirements, even though its depleted ancient waters can’t be replenished.
In India, the population has nearly tripled since 1970. Over-extraction of groundwater, especially in Punjab and Haryana, has depleted aquifers and contaminated rivers like the Ganges, threatening both agriculture and drinking water supplies.
6. Desertification: Population Growth Drives Soil Degradation
As population grows, so too does the livestock needed to feed it. Overgrazing has become a global scourge. Meanwhile, marginal lands are increasingly converted for cultivation by subsistence farmers desperate to feed growing families, leading to erosion and nutrient depletion.
The UN estimates that over one-third of Earth’s topsoil is already degraded. As food demand is projected to rise by 50% by 2050, the situation will almost certainly worsen. Traditional practices like fallowing (letting land rest) are no longer feasible when families constantly face food shortages. In countries like Niger and Ethiopia, land degradation is accelerating as farmers are forced to overwork depleted soils and compromise its fertility.
We Can Only Fix This By Addressing the Underlying Causes
Population growth is slowing globally—but it surely is not stopping. The world is still on track to reach 10.2 billion people by the 2080s. The associated environmental damages are often irreversible.
Many countries, however, have made dramatic progress through voluntary, non-coercive approaches. Bangladesh, Iran, and Thailand, to name but a few, have successfully lowered fertility through education and family planning initiatives. All these countries realized that sustainability is not just about consuming less, it’s also about how many consumers there are. With stable populations, environmental progress becomes possible.
Overpopulation remains an uncomfortable subject in most environmental circles. For decades now, many activists have avoided the issue, wary of accusations of racism or coercion. It is also true that the ongoing rise in per capita consumption contributes to adverse environmental impacts. But as my recent article confirms, the science is indisputable: demographic pressure is the primary driver of our planet’s degraded natural resources.
If we truly care about forests, fisheries, climate, biodiversity, water, and sustainable agriculture, we must speak up. Sustainable population policies must once again become a core part of global environmental discourse.
Dr. Alon Tal is a visiting professor at Stanford University and a faculty member at Tel Aviv University’s department of public policy.
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