Paul Ralph Ehrlich / Wikimedia

Paul Ehrlich, American biologist, educator and the president of Stanford’s Center for Conservation Biology. © Paul Ehrlich / Wikimedia CC 2.5 | Source: Greenpeace.

In 1968, Ehrlich published The Population Bomb, warning humanity that runaway human population would limit quality of life for humans, lead to increased starvation and malnutrition, and would contribute to ecological decline and biodiversity collapse.

At that time, the human population stood at about 3.5 billion. Now, 50 years later, it has more than doubled to 7.6 billion, and we face the most severe biodiversity collapse the Earth has seen in 65 million years.

Ehrlich, at 82, remains one of the most active, outspoken, and effective ecology activists on Earth. He still lectures at Stanford University in the US, and last year, the Vatican’s Pontifical Academy of Science invited him to Rome to speak about the causes of mass biological extinction.

Last July he wrote a piece entitled, “You don’t need a scientist to know what’s causing the sixth mass extinction” for the Guardian. Ehrlich points to two key drivers of ecological destruction: population growth and burgeoning resource consumption, especially by the rich.

Population and consumption

In 1972, when the Limits to Growth study appeared,  Greenpeace cofounders Ben and Dorothy Metcalfe attended the world’s first UN Conference on the Human Environment in Stockholm, with the intention of placing nuclear bomb testing on the conference agenda.

They met Ehrlich, who was there to add population growth to the agenda, as a driving force of ecological destruction.

The Metcalfes supported Ehrlich, but not all environmentalists – and none of the political delegates – agreed. The ecologist, Barry Commoner, argued against Ehrlich, insisting that human population growth did not pose a critical environmental threat.

Technology, he claimed, would allow us to feed billions more people. Commoner thought the more pressing issue was wasteful consumption by the rich.

Child in toxic e-Waste in China © Greenpeace / Natalie Behring

The real face of human technological expansion? © Greenpeace / Natalie Behring

Ehrlich agreed with Commoner that excessive consumption was a root cause of our problems, but maintained that ignoring population was a mistake. Regardless of technical progress, Ehrlich explained, population growth leads to habitat destruction, humanitarian catastrophes, and ecological decline. Ehrlich proposed universal women’s rights and a global contraception campaign to lower the human birth rate.

Ehrlich’s proposals, however, collided with cultural, political, and religious resistance. The Stockholm conference avoided discussing population, and the environmental movement since 1972 has largely ignored human population growth. Nevertheless, the nagging issue remains, four billion people later.

The limits are real

At the dawn of the industrial age, when Earth was home to only about one billion people, the English economist, Thomas Malthus, warned that an exponentially growing population on a finite planet would reach ecological limits.

Likewise, in Principles of Political Economy from 1848, the economist John Stuart Mill lamented the sprawl of cities, farms, and factories across the landscape, and advocated a “stationary state,” a limit to economic and population growth.

“The increase of wealth is not boundless,” Mill wrote, “A stationary condition of capital and population implies no stationary state of human improvement. There would be as much scope as ever for moral and social progress; as much room for improving the art of living, and much more likelihood of it being improved.”

However, those who profited most from human growth mocked Malthus and Mill, and still do. In our day, the profiteers also dismiss the 1972 Limits to Growth study, Ehrlich’s population warnings, and environmentalism in general, since neoliberal economic theory denies the limits of a finite planet.

Aerial View over São Paulo © Otávio Almeida / Greenpeace

Human expansion has altered much more than just the landscape. São Paulo from above © Otávio Almeida / Greenpeace

Technology advocates repeat endlessly that the so-called “Green Revolution” in agriculture enabled humanity to feed billions more people. But a closer look at factory farming reveals that the Green Revolution was actually a “black” revolution, fuelled by hydrocarbons and toxic chemicals.

Feeding billions led to ecological and health decline, the disruption of Earth’s nitrogen cycles, global heating, and the relentless excavation of nutrients from Earth’s fragile soils.

The European Union reports losing about a billion tonnes of topsoil annually, while over the last 25 years, Earth’s soil productivity has declined by over 50% in some regions.

75 billion tons of topsoil are lost annually worldwide from anthropogenic erosion. Crop yields are now stagnating in many regions and even where they’re rising, the increase lags behind population growth and rising demand, leading to higher food prices.

Fifteen years ago, David Pimentel warned that humanity and the ecosystems upon which it relies are “threatened by overpopulation.” Pimentel pointed out that in a world without fossil fuels, nations can support only about four people for every hectare of arable land. That means that most countries won’t be able to sustain even their current population, much less a growing one.

As ecologists from Malthus to Ehrlich have warned, humanity is now running into resource limits. The world’s wild fisheries catch stopped growing in the late 1980s, and has dropped by about 14% since, in spite of advances in fishing technology.

The amount of fresh water per capita has declined by over 25% since the late 1980s, and today, some 850 million people have no access to clean water. Five million people, including half a million infants, die each year from waterborne diseases.

In 2016, the United Nations “Global Material Flows” report showed that global resource depletion diminishes human health, quality of life, and future development. Although most nations still desire economic growth, the UN panel warned that “rapid economic growth … will place much higher demands on supply infrastructure and the environment’s ability to continue supplying materials.”

Numbers that matter

Those who criticised Ehrlich for his warnings in The Population Bomb, often site the fact that, since the 1960s, the population growth rate has declined from about 2.2% to 1.1% annually. This is true, but focusing on this percentage avoids the more relevant fact: the number of people on this planet has steadily increased every year.

Human population has been growing since time-immemorial, with two exceptions. About 2000 years ago, urban crowding, plagues, and warfare caused the population to decline for the first time in history.

Population growth recovered for a while, then declined again in the 17th century due to genocide and disease brought on by the European colonisation of Africa, Asia, and the Western Hemisphere.

Drought in Gallocanta Lake in SpainSequia España © Pedro Armestre / Greenpeace

Drought in Gallocanta Lake, Spain. © Pedro Armestre / Greenpeace

The growth rate recovered again by the time of Malthus, when a population of one billion people was growing by about 0.4% annually, adding about 4 million more people each year.

Later, the oil boom in the 1940s and 50s accelerated population growth. By the time Ehrlich wrote The Population Bomb in 1968, the growth rate had soared to 2.2%, the population to 3.5 billion, and we were producing 73 million more humans every year.

Modern contraception has allowed the growth rate to drop ever since, but only where women have freedom of choice and access to it. Today, although the growth rate has declined to 1.1%, the population has reached over 7.6 billion, and we’re growing more than ever before in history: 83 million more people each year.

Percentages can be misleading. As the percentage of starving people allegedly declines, the net number of starving people increases. About 1.5 billion people suffer from malnutrition, and about half of those (815 million people), go to sleep hungry every night. Nine million people starve to death every year. That’s one every 3.5 seconds.  There are more malnourished people today than the number of people alive at the time of Malthus.

The problem of scale

In 1993, at a scientific World Summit, 58 international science academies warned, “the magnitude of the [environmental] threat… is linked to human population size and resource use per person. Resource use, waste production, and environmental degradation are accelerated by population growth.”

Humans and human livestock now comprise about 98.5% of mammal biomass on Earth. Ehrlich points out that, “massive numbers of humans, their livestock and chickens” displace wildlife from available habitats and lead to the “disappearance of large, wild animals.”

He warns that, “increasing the scale of human enterprise, both population numbers and per-capita consumption, are still the main drivers of the extinction crisis.”

Amazon Rainforest in Burning Season © Otávio Almeida / Greenpeace

Large sections of the Amazon rainforest are set on fire every year by farmers to clear space for crops or cattle. © Otávio Almeida / Greenpeace

The challenge we face, as environmentalists, or as concerned citizens, is that “scale” is almost a taboo subject in public discourse. Since population and overconsumption remain two of the primary drivers of ecological destruction, perhaps we should take on the challenge of stabilising our population, along with managing over-consumption.

We cannot presume to engineer our way out of these ecological realities without attention to scale. We must embrace the nagging question of human scale, and recognise the need to slow down and control human enterprise.

“If you don’t have some sort of appreciation of the economy as being embedded in the natural systems of the planet,” urges Peter Victor from York University in Canada, “you’re not going to get very far understanding why we’ve got the problems we have with the environment, and how we’re going to solve them.”

The Population Bomb has been both praised and vilified,” Ehrlich wrote in 2009, “but there has been no controversy over its significance in calling attention to the demographic element in the human predicament … its basic message is more important today than it was 40 years ago.”


Paul Ehrlich, The Population Bomb, Sierra Club / Ballentine Books, 1968.

Paul and Anne Ehrlich: “The Population Bomb Revisited,” Electronic Journal of Sustainable Development (2009) (PDF).

Paul and Anne Ehrlich: Population, Resources, Environment, W. H. Freeman & Co, 1970.

Paul Ehrlich: “You don’t need a scientist to know what’s causing the sixth mass extinction” The Guardian.

“Yield Trends Are Insufficient to Double Global Crop Production by 2050,” Deepak K. Ray , Nathaniel D. Mueller, Paul C. West, Jonathan A. Foley, PLOS Journal, 2013.

“World Population, Food, Natural Resources, and Survival,” David Pimentel and Marcia Pimentel, World Futures, 59: 145-167, 2003.

“World population projected to reach 9.8 billion in 2050, and 11.2 billion in 2100: UN,” United nations Sustainable Development, World Population Project, 2017. Summary: UN, Full report: UNPD/WPP.

“The Human Ecological Predicament: Wages of Self-Delusion” William Rees, Professor emeritus, Human Ecology, University of British Columbia, Millennium Alliance for Humanity and Biosphere (MAHB), 2017.

“Harvesting the Biosphere: The Human Impact,” Vaclav Smil, Population and Development Review 37(4), PDR  2011)”

Regarding soil degradation, which you highlight, you can add these, which reference the “50% in some regions.”

“Land Degradation: An overview,” H. Eswaran, R. Lal, and P.F. Reich, International Conference on Land Degradation and Desertification; USDA and Oxford Press, India, 2001.

“Soil Degradation, Land Scarcity and Food Security,” Tiziano Gomiero, MDPI, 2016

“Comments on FAOs State of World Fisheries and Aquaculture,” Daniel Pauly, Dirk Zeller, Science Direct  Marine Policy, Volume 77, March 2017.