Several years ago, Bill Gates keynoted a breakfast for Seattle-based Climate Solutions, a nonprofit focused on advancing the clean energy economy and driving practical, profitable solutions to climate change. Gates opened his speech with an equation. To paraphrase: Our carbon problem = persons x services x the energy intensity of services x the carbon intensity of energy. The number of people is growing, Gates observed, and we all want more services. While Americans arguably consume too many goods and services, billions of people currently living in dire poverty need more. He then spent the rest of the time discussing the last two factors in the equation.

Recently, Robert Engelman and Samuel Codjoe published an article at Grist titled, “Hey, UN: Climate Change and Population are related.” They pointed out the fact that the United Nations would soon be hosting back-to-back conferences about population and climate change respectively, and they lamented that neither conference would likely address the concerns of the other. “That will be a missed opportunity,” they said, “because scientific research increasingly affirms that the two issues are linked in many ways.”

Engelman and Codjoe are not the only ones asking for a more open conversation about the relationship between family planning, population, and climate change. Articles in The New York Times and The Huffington Post also call for an increased focus on this nexus, both as a climate-resilience strategy and a means of reducing atmospheric carbon. The Aspen Institute has estimated that voluntary family planning for all who want it could provide 8 to 15 percent of needed carbon reductions. David Wheeler and Dan Hammer at the Center for Global Development argue that putting climate dollars into family planning programs (to make up for expected shortfalls) compares favorably to many investments in low-carbon technologies.

It doesn’t take scientific research or the brain of Bill Gates to figure out that our impacts grow as our numbers grow — that gains in the efficiency of, say, air conditioners or cars can be swamped by the growing number of air-conditioned houses and cars on the road. Analysis of population trajectories and effects seems like an obvious and necessary part of the climate dialogue. But in recent decades, public talk about population has been taboo, even among people who are keenly aware of the issues. If we are to foster a broader conversation about global warming, one that includes discussion of population, it is important to remember why the topic has been largely off limits for so long.

During much of history, male-dominated governments and patriarchal religions have treated a woman’s childbearing capacity as means to a societal or economic end. During the Iron Age, when the Bible and Koran were written, females, including daughters and wives as well as slaves, were literally chattel. To writers of these texts, a woman’s primary value lay in her ability to produce offspring of known lineage for her husband and his family. Martin Luther, father of the Protestant Reformation, echoed this sentiment: “Women should remain at home, sit still, keep house, and bear and bring up children … If woman grows weary and, at last, dies from childbearing, it matters not. Let her die from bearing, she is there to do it.” Some Christian leaders echo it still. America’s Quiverfull movement, as exemplified by the Duggar family, is a striking example.

As culture evolved, nation-state superseded kin and creed in terms of who or what might lay claim to a woman’s uterus. To this day, authorities sometimes exhort or coerce women to bear children as a service not only to husband and deity, but to country. Leaders may decide they want more workers, for example, or cannon fodder. Pronatalist policies are most common when leaders feel threatened by the economic or military strength of a neighboring region.

In the 20th century, a peak of pronatalist coercion occurred under Romanian dictator Nicolae Ceausescu, whose government (1965-1989) outlawed contraception, banned most abortion, and sometimes enforced these rules via mandatory gynecological exams. The movie 4 Months, 3 Weeks and 2 Days is a gut wrenching window into the lives of two young college friends under Ceausescu’s regime. Quasi-religious, quasi-political entities including Muslim theocracies and the Vatican also may pressure or coerce constituents to increase the birthrate. In August, after Iran’s Ayatollah Khamenei expressed alarm over declining birthrates, the national parliament responded by banning surgical procedures to prevent pregnancy.

Since modern contraception first was developed, governments have also used intimidation, coercion, and force on the other side of the equation. China’s one-child rule is a well-known example, as is India’s early attempt to set and meet population targets with enticements including transistor radios and cash incentives and, when those failed, deceit. Less known is the fact that in the 1990s, Peru’s government sanctioned the coerced sterilization of close to 350,000 poor and indigenous women. In the United States, poor and minority women and inmates have been sterilized without free and full consent, or, sometimes, when they were too young to give consent. This is not ancient history; abuses like these have been documented as recently as 2013.

Today, state-of-the-art family planning methods called LARCs (long-acting reversible contraceptives) are rapidly growing in popularity. These methods offer women an unprecedented ability to manage their fertility — to have children when they feel ready and only when they feel ready. On the Pill, which is 1960s technology with a few updates, one in 11 women gets pregnant each year. With a state-of-the-art “fit and forget” method like an IUD or implant, that drops below one in 500. Recent research in St. Louis and Colorado showed that when women are offered the method of their choice with no co-pay, most choose one of these LARC methods, and the rates of rapid repeat pregnancy, teen pregnancy, and abortion plummet.

Evidence keeps growing that these better contraceptives transform lives by improving maternal and child health, increasing education opportunities for young women and men, and helping families to thrive financially and psychologically. Based on this evidence, doctors, educators and social service providers are increasingly enthusiastic about these options. But women haven’t forgotten the dark and all too recent history of coercion, especially poor and minority women, and some communities and advocates are wary of the new methods and the enthusiasm. They are especially wary of any enthusiasm for solving societal problems by limiting women’s choices.

What if a woman wants to use a less effective method? What if she doesn’t know what she wants? It may be tempting for a provider to push whatever he or she thinks is best. And in the urgent press to solve enormous problems like poverty, hunger, or global warming, it may be tempting to treat a woman’s family-planning decisions as a means to a bigger end. It may be tempting, but it is wrong, and it doesn’t work. Yes, governments can and have forced the birthrate up or down, but only at a high cost in human rights and suffering, and with the added cost of undermining voluntary family-planning services.

The good news is that coercive population policies and targets are not only wrongheaded, they are not needed, because hundreds of millions of women want access to better family-planning methods that will let them delay, space, or limit their childbearing. In developing countries, more than 220 million women want to avoid pregnancy but are not using modern contraceptives. In developed countries, removing barriers to top-tier, long-acting contraceptives like IUDs and implants dramatically changes the rate of unintended pregnancy. Women have their own reasons for wanting contraceptives they can count on. They want to learn and grow, explore and contribute to the world around them, attain financial independence, and give their children the best possible shot in life. To borrow a phrase from poet Mary Oliver, each woman’s “one wild and precious life” is her own, and so are her reasons and goals for managing the wild and precious gift of her fertility.

This is not to say that health providers should be passive prescribers of whatever a woman might request, or that they should wait for clients to initiate family-planning conversations. It’s a provider’s job to be the expert on what technologies are available, including the risks and benefits of each, and it is a provider’s job to raise awkward and difficult topics. Every family-planning method has trade-offs and no one method works for all women, and ordinary women rely on their doctors to keep abreast of the options and make recommendations just as they would do in any other field of health.

Also we know that today, even in developed countries, many pregnancies result from inertia, impulse, inebriation, or some other factor that gets in the way of thoughtful, intentional life management. (Unfortunately, the fertility default setting is “on,” which means that when we aren’t paying attention or are dragging our feet or can’t decide, pregnancy can be the result. Some of the best modern contraceptives are game-changers precisely because they toggle the default, making protection the default and pregnancy an active choice.)

By using counseling techniques like “motivational interviewing” or “One Key Question,” providers can help women clarify their own preferences and even crystalize their long-term dreams and plans. Since so many births are simply the result of “go-with-the-flow” childbearing, it is important that educators and providers step up the conversations about family planning, opening this sometimes awkward topic in primary care visits, for example.

But all of these are client-centered approaches that respect the autonomy, dignity, agency, and intelligence of reproductive-age women. With women in the driver’s seat, improvements in care do produce a lower birth rate. But that is very different from providers or governments, even with the best of intentions, trying to force an outside objective. Vyckie Garrison, former leader in the Quiverfull movement, speaks eloquently about what it was like to have her childbearing be part of a social agenda (in her case driven by religion) and how this was abusive.

Human population has grown from 2 billion to more than 7 billion in the last 85 years, and policy makers do need to talk about the trajectories and the impact of population on war, food, water, health, fuel, climate, and more. They need to recognize that family-planning policies affect a host of other issues — that the question of whether women have reliable, safe, affordable, appealing contraceptive tools is a factor in infant health, family prosperity, education of girls and women, government budgets, and the functioning of our planetary life-support system. They need to be mindful about whether public policies or the structure of social services inadvertently nudge people to have more babies. They need to recognize that family-planning dollars are an upstream investment with known dividends and that empowering young women to make thoughtful, intentional childbearing decisions is a smart, cost-effective way to help ensure sustainable abundance for all. And they need to know that even in places like the U.S. and Canada, there’s a lot we can do right now to make a difference.

But as those policies are implemented, it is critical that we not forget how very wrong humanity has gone in the past when the life-giving power of a woman’s body became a tool in the hands of men on a righteous mission.