If you’re looking to reduce the pressure humanity is putting on the climate and global ecosystem, curbing population growth can’t help you much.
That’s the conclusion of new research published by the Proceedings of the National Academy of Sciences, which modeled various approaches to slowing population growth — from the reasonable to the monstrous to the completely catastrophic — to see how they’d play out. These included benign attempts to empower women around the world with greater access to contraception, economic development, family planning, and so forth; draconian legal measures to limit people around the world to one child per family; hundreds of millions of people dying due to food shortages; and several billion dying thanks to some form of global catastrophe.
The result? Only the truly ugly and unrealistic scenarios — a rapidly-enforced global one-child policy or the mass die-off of several billion people — altered population trajectories by 2100 enough to have a real impact on carbon emissions and resource use. In short, the morally defensible option for slowing down fertility (plus some of the indefensible ones) just didn’t do much good, still leaving the human population around 10 billion by 2100.
“No matter what levers you pull, we have such a huge demographic momentum, there’s no way we can rein in the human population fast enough to address sustainability issues in the next century,” Corey Bradshaw, the director of ecological modeling at the Environment Institute at the University of Adelaide in Australia, and one of the paper’s co-authors, told the Washington Post. “The population has this natural resistance to catastrophe.”
That will likely come as a surprise to some corners of the environmental movement, where there’s an undeniable fixation on the destructive consequences of population growth. And Bradshaw told the Washington Post’s Chris Mooney that whenever he gives talks about endangered wildlife around the world, “someone will stand up and say, ‘You’ve neglected the elephant in the room — human population size is the principal problem.’”
But to give that view its due, most of the data we have suggests population growth from 1961 to 2008 was a major driver of the pressure humanity is putting on the Earth’s biocapacity. And as Mooney notes, between 6.5 and 14 percent of all the human beings who have ever lived are alive right now according to some estimates.
But interestingly enough, Mooney also points out that the editor of Bradshaw’s paper was Stanford University’s Paul Ehrlich, whose 1968 book “The Population Bomb” largely introduced concerns over humanity’s numbers into the burgeoning environmental movement.
At any rate, what happened before and what we can do going forward are two different things. Population growth trends for the rest of the 21st Century are “virtually locked-in” as Bradshaw put it. And the ways we can make at least some dent in global population growth — economic development of poor countries, more education and gender egalitarianism for women, greater voluntary access to contraception — are all things we should be doing regardless.
Which doesn’t mean we shouldn’t try. Common estimates generally say humanity will peak at around 10 billion by 2100, then naturally plateau or even begin falling after that — or perhaps even peak sooner, around 2050 at 8 billion. Other estimates, however, suggest we could go considerably higher; to 12 billion by 2100.
And the human beings most threatened by the consequences of this are the global poor. “The greatest threats to ecosystems — as measured by regional projections within the 35 global Biodiversity Hotspots — indicate that Africa and South Asia will experience the greatest human pressures on future ecosystems,” according to the study. Those are the same areas of the world where the global poor are the most vulnerable to the extreme weather, resource disruptions, and other challenges that will come with climate change.
That leaves systemic changes to societies’ resource use, its forms of energy, its economic structures and its social organization as the crucial moves that can lead to a sustainable civilization. As Ryan Cooper argued at The Week, carbon emissions per person vary wildly even within advanced countries — 5.6 metric tons in France, 11 metric tons in Norway, 5 metric tons in Switzerland, and a whopping 17.6 metric tons in the United States — and the energy use per person even for someone who’s homeless in America is twice the global average. (For well-off Americans, it’s ten times the size.) When it comes to land use, the density of our communities and living arrangements make a far greater difference than our sheer numbers. All of which suggests there are enormous structural changes we could undertake to reduce our emissions even as our populations keep growing.