Discredited 18th-century economist Thomas Malthus still haunts the environmental debate.

"We are in the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth," said climate activist and Time magazine person-of-the-year Greta Thunberg before the United Nations in the summer of 2019. "How dare you!"

Some praised Thunberg's performance as a stinging rebuke to the rich and powerful for failing to put the survival of the planet above their own needs. Others saw the exploitation of a young woman with emotional problems for propagandistic ends.

There's no question that Thunberg's style of environmentalism — strident, urgent, and critical of global capitalism — has gained a strong foothold in contemporary politics.

Other local mentions of climate change

LETTER TO THE EDITOR: Deny climate change and deny reality

Trump lauds US economy in Davos, says little on climate woes

Australia’s hellish wildfires imperil thousands and renew focus on climate change

A 2019 paper from the journal Bioscience, co-signed by more than 11,000 scientists, asserted that Earth's population "must be stabilized — and, ideally, gradually reduced."

Fears of overpopulation and ecological disaster are also beginning to manifest on the far right, mixed in with an anti-immigrant animus.

Whether contemporary proponents of these ideas know it or not, they are all the intellectual heirs of the misguided 18th-century thinker Robert Thomas Malthus, who believed that when human population increased, famine and environmental destruction would ensue.

Reason's science correspondent Ron Bailey, who is the author of the 2015 book “The End of Doom: Environmental Renewal in the Twenty-first Century,” says that Malthus failed to see that as human population increased, so too would livestock and crop populations with the help of ever-improving agricultural technology, which is why food availability steadily increased over the past two centuries, outpacing population growth.

"Basically, the Malthusian prescription turns out to be completely wrong," says Bailey.

In the contemporary world, Malthusianism was most famously expressed through the work of ecologist Paul Ehrlich, especially in his 1968 book, “The Population Bomb,” which predicted that through the 1970s and '80s "hundreds of millions would starve to death."

Ehrlich, who still holds an endowed professorship at Stanford, didn't respond to our interview request. But his proposed solutions at the time included taxing diapers, subsidizing vasectomies, and even spiking food aid and water supplies with sterilizing drugs and then holding a lottery for access to the antidote.

Ehrlich turned out to be as wrongheaded as Malthus. In the half-century after Ehrlich made his dire prediction, calories available per capita steadily increased in just about every region of the world thanks largely to improved agricultural techniques and technology.

And yet world hunger has yet to be eradicated, with the United Nations reporting that about 10 percent of the global population is undernourished.

Is it really possible that the world could run out of food?

While the International Food Policy Research Institute projects that farmers will have to produce 70 percent more food over the next 30 years to feed everyone on the planet, the technology already exists to accomplish that goal. Agronomist Paul Waggoner calculates that if all farmers became as efficient as today's U.S. corn growers, the world could feed 10 billion people today on half as much land.

Today's Malthusians are most concerned about the disruptive effects of climate change. Citing global warming and habitat destruction, documentarian David Attenborough described humanity as a "plague upon the Earth."

Meanwhile, the Bioscience paper signed by 11,000 scientists projects total societal collapse if population isn't managed properly.

"I think that there's a kind of a catastrophizing, apocalyptic undercurrent," says Ted Nordhaus, founder of the Breakthrough Institute, which advocates technological solutions to environmental problems. He believes the environmental movement has long been hindered by its anti-growth paradigm.

Nordhaus says that the most effective way to deal with climate change is by promoting policies that accelerate economic growth.

Most of today's environmentalists don't openly advocate for the draconian population-control measures pushed by Ehrlich and other Malthusians in the 1970s.

Karen Pitts, who is a member of the Sierra Club and ran a Northern California sub-committee on population growth, says she just wants more sex education and greater access to birth control in the developing world, pointing to a project she participated in with Tanzania's local population where the introduction of contraception drastically reduced unwanted pregnancies.

Funding greater access to birth control and education for women in developing countries was also a recommendation of the Bioscience paper. It's also a policy agenda of the U.N. and many leading NGOs like the Bill and Melinda Gates Foundation.

Nordhaus says such measures can help at the margins but ultimately miss the big picture, which is that as wealth increases, fertility rates naturally fall as families invest more resources in fewer children.

The Biosciences paper argues that economic growth is driving overconsumption of resources and says "our goals need to shift from GDP growth and the pursuit of affluence toward sustaining ecosystems."

"I don't think we're keeping up with population growth and increased consumption," says Pitts. "As soon as we find new ways to do it, our consumption increases. That's the problem.“

Pitts is right that people in wealthier societies tend to consume resources and generate greenhouse gas at rates that are orders of magnitude higher than those in the third world.

But Nordhaus points out that when poor societies become wealthy there are more people positioned to help solve environmental problems in the only way that really works — with new technology.

And so Nordhaus advocates for greater reliance on clean, abundant energy like nuclear power to fuel advanced economies towards possibly innovating even lower impact alternatives.

Malthus wasn't completely wrong about the tendency of humans to deplete resources, says Bailey. But Malthus failed to see that new ways of organizing society would ameliorate the problem.

"The world understood the role of property rights, the rule of law," says Bailey. "And this dramatically changed the incentive structures that people had prior to that."

Zach Weissmueller is a writer and video journalist who's been producing documentary shorts, video interviews, and feature articles for Reason TV and Reason.com since 2010.