In a classic case of confusing root causes with symptoms, an environmental report on the United States’ rising contribution to climate change over a recent 15-year period was titled The Carbon Boom.

It should have been titled The Population Boom, as virtually the whole increase measured in carbon dioxide emissions came from more people, not from burning more fossil fuel per capita.

This remains all too typical, approaching every environmental solution in terms of reducing our carbon (or nitrogen or land-use) “footprint,” lowering our per-capita impacts — seldom even discussing the other major part of the solution, the size of the population.

It is a big reason a sustainable Chesapeake Bay and a sustainable planet may always elude us. Around the Chesapeake, where we’re adding more than a million people a decade to the watershed, failure to even discuss our numbers is a huge missing piece of the cleanup.

So it’s good to see well-reasoned research published this month in the Journal of Social Theory and Practice that makes the case that reducing population growth to prevent a climate disaster is both necessary and morally justified.

In their paper, Population Engineering and the Fight Against Climate Change, Travis N. Rieder, a Johns Hopkins bioethicist, and his colleagues Jake Earl and Colin Hickey, of Georgetown University, examine a range of techniques societies could use, or use more widely, to slow and stabilize population. The possibilities go from simply making more family planning choices available, through advertising and other media campaigns, to stronger incentives and disincentives such as tax policies.

The authors, all moral philosophers, rule out the most coercive policies such as sterilization and mandated family sizes; and they would aim stronger population-slowing measures at wealthier and more developed countries to avoid pitfalls of unfairly targeting those poorer, more desperate and less educated.

“The right to a family size of your choice,” Rieder said in an interview, “is like most absolute rights — tempered by the well-being of family, community and society.” An estimated 250,000 additional people will die globally by mid-century if climate change is not soon held in check, Earl noted, “so this is not anti-people.”

Relatively modest changes in the number of children per couple would make for big climate change progress, the authors say. If couples worldwide averaged producing half a child fewer than they do now, it would cut carbon emissions by 2100 by about 5 billion tons (more than half of all the CO2 emitted globally in 2013).

Even by around 2050, we’d get at least as much bang for the buck from that lowered birthrate as from doubling the miles per gallon for all cars, increasing wind energy 50-fold, or tripling nuclear energy (which emits no carbon).

Conversely, if we go about adding billions more people, as currently projected by the United Nations, to meet world goals for avoiding the worst of climate change, we’ll have to shrink our carbon footprints by up to 70 percent in the next few decades — and become a virtually carbonless society by century’s end.

The authors — and most scientists — think doing that ranges from unlikely to impossible. This illustrates another big flaw in relying just on reducing per-capita environmental impacts. To the extent we assume that is our only choice, we don’t analyze the likelihood and costs of making the often-huge footprint reductions that real sustainability would require.

The authors point out that our reproductive choices have a “carbon legacy,” as every child’s contribution to climate change continues for generations and expands with that child’s children and grandchildren, and so on. It’s enough to utterly swamp all the reductions one might make in their own impacts.

Rieder, who has one child, age 2½, and has written previously about the ethics of small families and adoption versus having babies, said that a recent airing of the paper on National Public Radio elicited some hate mail — “baby haters use global warming” said a correspondent in The Federalist — and tweets like this one: “he and his family should just kill themselves.”

“But we also received more than 100 “thank you” emails,” Rieder noted, as well as a more mixed response. “Several women said, ‘Empower women, don’t focus on our reproductive rights,’” he said. This reflects a larger split that has persisted for a couple decades between feminists and the world’s population reduction activists.

A widespread critical reaction that the authors said they take seriously was the concern that a world with fewer people won’t be able to maintain prosperity in a world economy based on never-ending growth. “That will be the subject of our next paper,” Rieder said.

It struck me that many longtime ecological economists, an established subset of economics that is all about prosperity without endless growth, might see that next paper as the re-invention of the wheel. I know some veteran population activists feel that way about the recently published research of Rieder, Earl and Hickey.

But bring it on. Their research can only increase the willingness to discuss population as part of the sustainability puzzle. It’s a conversation too often missing from the environmental movement.

The views expressed by opinion columnists are not necessarily those of the Bay Journal.

Tom Horton, a Bay Journal columnist, has written many articles and books about the Chesapeake Bay, including Turning the Tide and Island Out of Time. He currently teaches writing and environmental topics at Salisbury University.

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