A right-wing attack on presidential science adviser John Holdren earlier this year scratched the surface of a long-running conversation about population and the environment. After the Senate confirmed Holdren for his dual post as the director of the Office of Science and Technology Policy, conservative bloggers, pundits, and the Washington Times railed on him over sections of a 1977 textbook, Ecoscience: Population, Resources, and Environment, for which Holdren was the third author, with Paul and Anne Ehrlich.

The critics focused on portions of one chapter in the 1051-page book describing various population control measures tried or proposed around the world—some of them extreme and coercive. Cherry picking language from the text, they claimed that Holdren’s aim was to corral population growth through forced abortions or mass sterilization. As Chris Mooney explained after retrieving a copy of the book from a university library, describing such measures does, of course, not amount to endorsing them. Moreover, the authors in fact concluded that the best way to slow population growth was to increase access to family planning resources like birth control. Just as he did during his confirmation hearing, Holdren explained in response to the attacks that he rejects the idea of government-enforced population controls. In fact, what he said during the hearing was this: “When you provide health care for women, opportunities for women, education, people tend to have smaller families on average,” and in reference to global climate change, “it ends up being easier to solve some of our other problems when that occurs.”

The attacks on Holdren eventually dissipated, but the whole kerfuffle did raise the question of how best to talk about the complex relation between population and environmental sustainability. According to Shira Saperstein, Senior Fellow at the Center for American Progress and the Deputy Director and Program Director for Women’s Rights and Reproductive Health at the Moriah Fund, many debates over the issue since the 1960s have been simplistic. She summarizes the thrust of Paul Ehrlich’s 1968 book, The Population Bomb, as “more people equals more damage—and the answer to that is fewer people,” a conclusion she rejects. There is a relationship between population and environment she says, “but it is far more complex than people have acknowledged in the past. I think partly because we looked at these simplistically in the past, we made a lot of mistakes.”

Saperstein spoke with Science Progress about a new framework for thinking about population and sustainability based on social justice in a recent podcast conversation. Joining her were Laurie Mazur, director of the Population Justice Project and editor of the new book, A Pivotal Moment: Population, Justice, and the Environmental Challenge, and Brian O’Neill, a scientist with the Institute for the Study of Society and Environment at the National Center for Atmospheric Research in Boulder, Colorado. “So much of the resistance to talking about population issues comes from a fear of where it’s headed,” Mazur acknowledges, “So many people are legitimacy concerned that concern about the global environment will take us back to the bad old days of population control.” For a full recording of the conversation, please see the audio available at the top of the page.

Population programs of the past, Saperstein says, “were too often focused on demographic targets, on limited births, on controlling population, rather than empowering women to make their own autonomous choices.” The worst programs following this logic resulted in sterilization campaigns in India and policies for forced abortions in China. The proper approach, the three experts say, is to realize that there is a significant unmet demand for family planning and reproductive health services around the world. Providing women with the opportunity and resources to make meaningful decisions about when and how many children to have gives them more control over their economic future while protecting their human rights. Given those choices, women tend to have smaller families. And over the next century, a secondary result of slower global population growth could be a significant reduction in greenhouse gas emissions, the three experts explain.

“Population matters,” says O’Neill, “It is not the largest impact on emissions—it’s not zero either.” He admits that while that sounds like a wishy-washy middle-ground conclusion, it’s important because of long-running debates between those arguing that population is the most important consideration for evaluating human impact on the environment and those who say it has nothing to do with it at all. “You’re not going to solve he climate problem—or probably any other environmental problem—just by slowing population growth,” he says. But development pathways and the nature of economic growth around the world provide the context in which societies must address climate change. As Mazur and Saperstein explained in a recent column, “In developing countries, urbanization is associated with rising per-capita emissions; as populations age, their per-capita emissions decline.” So population is one part of that social context.

Explaining the scientific research on the relationship between population and environment is one thing, O’Neill says, but the context for these conversations is equally important. A growing body of technical research helps, but he emphasizes that experts must understand the history and the legitimate concerns that people have about raising the issue of population-related policy as a means to environmental or even other development ends. “I think that a lot of time scientists get in trouble on this issue—and these are scientists who don’t work on population and environment,” he says, “because for some reason they feel free to talk about it as if they know what they’re talking about when they actually don’t.”

O’Neill says this is incongruous because in the case of climate change, “Someone who studies sea level rise would be pretty careful talking about ecosystem change because they know they’re not an ecologist and maybe they don’t exactly know what they’re talking about. But all of a sudden it’s a population issue and they feel free to say anything that comes into their head.”

Scientists, he says, are learning that an informed conversation more attuned to the social justice goals of population advocates is important. “Population, demographic change, does have consequences for emissions—and it’s okay to raise that,” he says, “It does not mean necessarily that it follows that demographically related policies are the best way to respond to climate change.”

Andrew Plemmons Pratt is the managing editor at Science Progress.

Dire warnings like these cue the chorus of population deniers, who assert that growing human numbers pose no problem at all. They point out that Paul Ehrlich’s predictions have not come to pass, and that human ingenuity can keep pace with our growing numbers.

For some, population denial springs from fear that the Malthusians will trample human rights in their pursuit of lower birthrates. Such fears are well founded, as current policies in China and the history of population control in India and elsewhere vividly illustrate. Others are concerned that a focus on human numbers will distract us from bigger issues, like inequality and unsustainable consumption. And then there are the religious conservatives who fear (again, rightly) that family planning and women’s empowerment will upend traditional gender roles.

Now the Malthusians and the population deniers are duking it out about climate change. It’s not hard to understand why this is such a volatile issue—population touches on some of the most intimate and value-laden aspects of life: sex, gender, religion, and culture, as well as questions of equity and social justice. But viewing population in such all-or-nothing terms does little to advance understanding—or action—on this important issue.

So, before we settle in to another round of polarized, self-defeating debate, let’s try to separate ideology from evidence. New research has given scientists a more sophisticated understanding of population dynamics and their environmental impact—which could be the basis for sound and effective policy.

Scientists have learned that population dynamics (not simply fertility rates, but population composition—age and gender, and distribution—patterns of migration and urbanization) have a significant impact on the natural environment. A wide range of mediating factors, including technology, consumption patterns, economic policies and political choices shape that impact, however, and it is neither linear nor uniform.

Americans, for example, comprise only 5 percent of world population, but produce a quarter of all carbon emissions. In developing countries, urbanization is associated with rising per-capita emissions; as populations age, their per-capita emissions decline.

Does that mean human numbers, per se, are irrelevant? Not exactly.

First, remember that population is still growing rapidly. While the rate of growth has slowed in most parts of the world, our numbers still increase by 75 million to 80 million every year. Choices made today will determine whether human numbers climb from today’s 6.8 billion to anywhere between 8 billion and 11 billion by mid-century.

Almost all of that growth will take place in the developing countries, which is also where rapid development must occur so that the three billion people who now live on less than $2 a day can escape from poverty. For us in the affluent countries, the problem is overconsumption—our bankrupt economic system devours natural resources, yet fails to meet human needs. For people in the developing world, the problem is underconsumption; that same economic system fosters poverty and inequity that deprives people of the resources they need to survive. So we need to consume less, they need to consume more, and we all need to consume differently—to find ways to meet human needs without destroying the natural systems that sustain life.

If we take seriously the need to protect the planet and distribute its resources more equitably, it becomes clear that it would be easier to provide a good life—at less environmental cost—for 8 billion rather than 11 billion people.

Take climate change, for example. An analysis of climate studies by Brian O’Neill at the National Center for Atmospheric Research shows that slower population growth could make a significant contribution to solving the climate problem.

Imagine a pie divided into slices—each representing an action begun today that would eliminate 1 billion tons of carbon dioxide per year by 2050—for example, widespread implementation of energy efficiency measures and the adoption of renewable energy sources. Seven slices are needed to avert disastrous climate change. O’Neill estimates that stabilizing world population at 8 billion, rather than 9 billion or more, would provide one “slice” of emissions reductions. That would eliminate as much carbon dioxide as completely ending deforestation.

Of course, slowing population growth is not all we must do. Current consumption patterns are unsustainable, regardless of our growing numbers, and continued reliance on fossil fuels could easily overwhelm any carbon emission reductions from slower growth. Still, slowing population growth is a piece of the “pie.”

But if we seek to address population growth, we have to do it right. That is, we have to learn from the history of bad population policies, which have veered between top-down “population control” schemes that violate human rights, and ideology-driven “abstinence only” programs that ignore the reality of human sexuality.

We have to focus on what works—and what we should be doing anyway as a matter of basic human dignity and social justice: making sure that all people have the means and the power to make real choices about childbearing.

What does this mean? It means expanding access to voluntary family planning and other reproductive-health information and services. It means promoting education and employment opportunities, especially for women and girls. And it means tackling the deep inequities—gender and economic—that prevent people from having and acting on meaningful choices about childbearing. Each of these interventions is vitally important in its own right as a matter of human rights and social justice.

Today, we have an extraordinary opportunity to make progress on these issues. After eight long years, we finally have a president—and a secretary of state—who are willing to make policy decisions based on evidence, not ideology.

But that opportunity will pass us by if progressives remain stuck in the tired debates of the past. The Malthusians and the population deniers are both wrong. Rapid population growth is not the primary cause of our environmental crises, and slower growth is not a panacea. But addressing population growth by the ethical means outlined above is part of what we must do to build a sustainable, equitable future. It’s time to have a new conversation about population and the environment—one that is grounded in science and guided by values of human rights, equity, and social justice.

Laurie Mazur is the director of the Population Justice Project and editor of A Pivotal Moment: Population, Justice, and the Environmental Challenge. Shira Saperstein is a Senior Fellow at the Center for American Progress and the Deputy Director and Program Director for Women’s Rights and Reproductive Health at the Moriah Fund.