Conservation news

Unrelenting population growth driving global warming, mass extinction

Scientists need to start speaking out on overpopulation

Suburb development in Colorado Springs, Colorado U.S. The population of the U.S. is currently growing at around 0.7 percent annually. Photo by: David Shankbone.

It took humans around 200,000 years to reach a global population of one billion. But, in two hundred years we’ve septupled that. In fact, over the last 40 years we’ve added an extra billion approximately every dozen years. And the United Nations predicts we’ll add another four billion—for a total of 11 billion—by century’s end. Despite this few scientists, policymakers, or even environmentalists are willing to publicly connect incredible population growth to worsening climate change, biodiversity loss, resource scarcity, or the global environmental crisis in general.

“We are already to a point where our population size is unsustainable,” Jeffrey McKee with the Ohio State University told “In other words, we are already beyond the point of the biological concept of ‘carrying capacity.’ Millions of people go hungry every day, and an unfathomable number don’t even have access to clean drinking water. A world of 11 billion people would be regrettable to humans as well as to other species.”

McKee has recently studied the intersection between human population and biodiversity decline, finding a direct correlation between the rate of population growth and the number of endangered species in a country.

Meanwhile another researcher, geographer Camilo Mora with the University of Hawaii, recently argued in a paper in Ecology and Society that overpopulation was exacerbating global warming, the biodiversity crisis, as well as creating large-scale economic and societal problems.

But if our population is already beyond sustainable, why has the subject become almost taboo? And not just in political circles, but even in environmental circles?

“There are multiple reasons including historical flip-flops about [overpopulation’s] importance,” Mora told “However, the fact that were are not interested in talking about it it does not make less critical.”


An endangered lemur: the Coquerel’s sifaka (Propithecus coquereli). The IUCN Red List recently announced that 94 percent of the world’s lemurs are threatened with extinction, making them one of the most imperiled groups. Lemurs are only found on the island-nation of Madagascar. While the primates are vanishing, the human population has soared. Currently growing at around 2.8 percent, over 40 percent of the island’s population is under 15. Photo by: Rhett A. Butler.

For decades scientists have been warning that the world may well be entering a period of mass extinction with untold consequences for human societies and the natural world. While the drivers of global biodiversity decline are many and complicated—including habitat destruction, deforestation, overexploitation of species, climate change, and ocean acidification—they are also underpinned by one simple fact: the human population continues to boom.

“It is simple math,” Mora told “We live in a world with limited resources and space. The more we use and take the less other species have. Today some 20,000 species may be driven to extinctions due to habitat loss alone.”

In fact, a study by McKee and colleagues last year in Human Ecology directly linked the rate of national human population density and growth with a rise in endangered species, as represented by mammals and birds on the IUCN Red List.

“It was found that the sum of threatened species per unit area could be best explained by two variables: human population density and
species richness,” the scientists write. Adding in gross domestic product (GDP) and agricultural land versus endemic species (species found no-where-else) improved the model, but the strongest indicator proved human population.

The expected population changes in the millions from now to 2100 are shown in the graphic. Map by: UW Center for Statistics and the Social Sciences.

In fact, looking at only population the researchers found that for the average country with a growing population—which includes the vast majority of nations on Earth—the number of threatened birds and mammals would rise by 3.3 percent in the next ten years and by 10.8 percent by 2050.

However, the reverse is also true. In the 21 countries where human population is expected to drop, the researchers predicted that the number of threatened species would fall by 2.5 percent by 2050. Of the 12 countries that have already seen some population decline, nine have seen their percentage of threatened species drop.

“It was somewhat reassuring that in most of the countries where the population decreased in size, there was a small but noticeable decrease in the number of mammals and birds that were threatened with extinction,” McKee said.

While the paper doesn’t theorize why population density and growth corresponds to a rise in threatened species, the answer is likely straight-forward.

“Every human being uses resources for food, shelter, and comfort. Even if these resources are used efficiently and wisely, each individual depletes the resources necessary to sustain other species,” said McKee. “So the more of us Homo sapiens there are on this planet, the more biodiversity will suffer.”

Global warming

Wodaabe women in Niger. This West African country has the world’s highest fertility rate. In 2010, the World Bank estimated a total fertility rate (the number of children born on average of each woman) of over seven. Photo by: Dan Lundberg/Creative Commons 3.0.

Most scientists now agree that global warming is the greatest environmental crisis on the planet today, and many would say it’s likely the greatest crisis humans are facing altogether. Solutions to global warming have long focused on kick-starting a renewable energy revolution, along with preserving standing forests and transforming agriculture. However, Mora argues that ignoring population growth makes it incredibly difficult to achieve the needed carbon cuts.

“In the United States, each child adds about 9,441 metric tons of carbon dioxide to the carbon legacy of an average parent, which is 5.7 times his/her lifetime emissions,” Mora writes in his paper. “Achieving a reduction of greenhouse gases will become increasingly difficult even under modest population growth rates given expected improvements in human welfare and expected increases in energy consumption.”

Despite the role of population growth—combined with rising consumption—in exacerbating climate change, Mora said the world has recently turned a blind eye to the problem.

“The most authoritative report on climate change [i.e. the Intergovernmental Panel on Climate Change] makes little to no reference to the issue of population growth or family planning, or any related matter,” he writes, adding that funding contraception for women who don’t have access would be an incredibly cheap option for curbing climate change.

According to research from the United Nations Population Fund, over 200 million women would like, but lack access to, family planning. The result? Over 70 million unwanted pregnancies.

The silent crisis?

Traffic jam and crowded streets in Ho Chi Minh City, Vietnam. Photo by: Ngô Trung/Creative Commons 3.0.

So, if a rising population is one of the driving forces behind mass extinction and global warming then why isn’t overpopulation on the agenda? In fact, it’s not only politicians and governments that appear reluctant to discuss overpopulation, but also scientists, conservationists, and environmentalists.

“Nobody wants to talk about ‘population control,’ and rightly so. There are basic human rights of reproduction, family values, cultural values, and even economics that plays into these considerations. These are touchy subjects,” said McKee. “But even talking about ‘reproductive responsibility,’ my preferred term, can rub people the wrong way.”

To make matters more complicated, many economists have argued that slowing population growth is a death knell for the economy, arguing that fewer young workers entering an economy makes it more difficult to fund social programs and government. Such fears have led to many countries implementing policies to raise populations, not lower them.

In 2006, then president of Russia, Vladimir Putin, set up a ten-year program to dramatically raise the number of children born in the country. In 2009, the country recorded its first population growth since 1991.

Japan’s demographic decline—the population recorded its first drop in 2008—led to the creation of a ministerial post focused entirely on raising fertility in the country. Now, the nation is mulling mass-immigration. Yet, Japan sports one of the densest on the planet with more people per square kilometer than even India.

Most recently, Iran’s Supreme leader, Ayatollah Ali Khamenei, issued an edict calling for a massive birth rate increase. Though Iran’s population is expected to continue rising until mid-century, its birth rate has fallen in recent decades.

“In short, bringing up the issue of human overpopulation will not get you elected, and taking responsibility for the issue once in office will not get you re-elected,” noted McKee.

But Mora said the belief that population growth is necessary to economic prosperity is simply erroneous.

Human population growth over the last 12,000 years. Population has exploded since around 1500.

“If population growth was key to economic [development] Africa will be the richest continent in the world,” he told Mora said that population growth can actually stifle an economy, creating a deficit of jobs for a booming young population which in some countries has resulted in social unrest. Moreover, too many young people can also create an education burden, resulting in lower government revenues over time.

“When a social system is maxed that means that the quality of services will reduce…Just consider the likely differences in tax revenue generated by a person whose society allows them to get to university versus an individual that may not finish high school,” said Mora. “That is just one example, but we also do have shortfalls on health and recreation. We can achieve economic growth [through] training and innovation rather than adding more people with limited chances to succeed. ”

Moreover, for a long time, some experts predicted that the overpopulation problem would largely take care of itself, arguing that populations would peak at around 9-10 billion by mid-century and then begin to fall. Yet, such estimates now appear optimistic. A new prognosis by the United Nations last year predicted that our global population will continue growing through the century, hitting 11 billion by 2100, largely due to population booms in Africa. So, while the rate of overall population growth may be slowing, trends don’t show a peak population anytime soon.

“Two of the greatest concerns of our generation are to improve human welfare and to prevent the ongoing loss of biodiversity. More than one billion people live in extreme poverty and hunger, and ecosystems are losing species at rates only seen in previous mass extinction events. Unfortunately, overcoming these problems remains difficult, and if anything, progress appears to be leaning in undesirable directions,” Mora writes.

In fact, demographers says Africa could see its population rise from 1.1 billion today to 4.2 billion by 2100. If such growth occurs, it’s hard to imagine what will happen to Africa’s rich, but already greatly-imperiled, biodiversity. Moreover, Africa remains the least food-secure continent on the planet with many of its countries today facing food shortages amid social unrest and conflict.

Can we tackle population growth?

Crowd from above. Photo by: Public Domain.

But how do you approach, let alone solve, something as sensitive as population growth? One of the reasons why the subject is so touchy is that it conjures up images of totalitarian states decreeing one child per family, forced abortions or sterilizations, and even genocide. But experts say that access to contraception and education for women are actually the best ways to curb global population.

“Simple solutions such as empowering women, sex education, providing affordable family planning, revisiting subsidies that promote natality, and highlighting the economic cost and necessary investment for children’s future success could considerably avert population
growth,” Mora writes, adding that he’d like to see an education campaign to raise awareness about the impacts of a rising global population.

“I prefer to have the freedom of choice, but informed choice,” he told “Just like we did with tobacco and HIV where information created a global awareness about the issues. They are still present but people are more conscious about it.”

Instead, according to Mora, the issue is ignored or even considered something of a badge of honor. He points to the U.S. where the hugely popular show 19 Kids and Counting (previously 17 Kids and Counting, and 18 Kids and Counting) celebrates the unusually-large Duggar family.

“Pure irresponsibility and we make a fun of it!” Mora noted. The parents of the show, Jim Bob and Michelle Duggar, have stated that religious beliefs were one of the primary reasons they stopped using contraceptives. For many, religious convictions still play an important role in the decision to have large families or avoid contraceptive-use. But Mora believes, even here, change is possible.

“Religions change slowly, but they change. If we get started in an intellectual revolution on how important this is, religions will have no choice.”

Both Mora and McKee agree that the first step is for scientists—including environmentalists and conservationists—to stop avoiding the issue of overpopulation, but instead incorporate it into their research, their work, and their message.

“[Overpopulation] must be embraced, not eschewed,” said McKee. “My team’s research has shown that considerations of human population density must be part of any comprehensive conservation plan. The sooner we open the difficult dialogue, the better.”


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