By Alisha Graves

There’s no single solution for climate change, no magic bullet that can stabilize and eventually reduce the concentration of greenhouse gases in the atmosphere. But separating sex from childbearing represents an underappreciated opportunity to forestall climate disaster.

To be sure, addressing the climate challenge will require a wide range of approaches. Conservation policies must be implemented, and major investments are needed to develop and scale up renewable energy technologies. But another opportunity—often overlooked—is ensuring that every woman has both the information and the means to separate sex from childbearing. All over the world, whenever good family planning programs are put in place, couples choose to have fewer children. The family’s health benefits, household resources per capita increase, and each couple’s carbon footprint shrinks.

Perhaps the most important equation in the world is one made famous by John Holdren, formerly a science and technology advisor to President Obama, and biologist Paul Ehrlich: I=PAT. “I” stands for impact on the environment, “P” for population, “A” for affluence, and “T” for technology. Technology can either ameliorate or intensify human beings’ impact on the environment—but affluence and population have a straight multiplying effect. That is, affluence leads to increased consumption and pollution. Higher population means more carbon footprints on the biosphere. But there’s a twist: Since per capita emissions in wealthy countries are much greater than in low-income countries, averting an unintended pregnancy in a high-emitting country will do more to help the climate than will averting a similar pregnancy in a low-emitting country.

Though many people acknowledge population’s impact on the environment, few go on to mention that population growth is not a fait accompli. In industrialized countries, the average family in the middle of the 19th century had six or more children. Today, families in such countries produce on average about 2.4 children (near replacement level). More recently, in some developing countries, birth rates have fallen remarkably quickly, as in Iran, whose total fertility rate fell from more than five to less than three in just seven years. The fertility rate in Thailand, when voluntary family planning and safe abortion became widely available, fell from six children to 3.5 in 12 years—though it had taken the United States 58 years to make the same transition in the 19th century.

Coercive approaches to population, such as China’s one-child policy and forced sterilization in India, should have no part in family planning. But when women are denied the information and means to separate sex from childbearing, pregnancy itself is coercive. So family planning services, from design to implementation, mustn’t be about telling couples what to do; the point is giving couples what they want. The good news is that many family planning programs around the world do just that. In particular, they uphold a woman’s right to determine how many children she has and when she has them.

For the climate, family planning’s potential benefits are profound. A careful study of a voluntary family planning program in California demonstrates that family planning is the single most cost-effective way to abate carbon dioxide emissions. Spending $24 on wind energy averts 1 metric ton of carbon dioxide emissions. So does spending $51 on solar energy. But spending just $7 on family planning achieves the same result.

Lessons of the Sahel. Family planning as a means for mitigating climate change is a familiar enough idea, but family planning for adapting to climate change may sound far out. It is not. Because climate change negatively affects some staple crops, it worsens food insecurity in parts of the world. But according to a 2012 study that modeled climate change, food production, and population growth in Ethiopia, achieving low fertility by 2050 might fully make up for climate change’s negative effects on Ethiopian agriculture. (A lower overall population means more calories are available per person.) Perhaps more tellingly, some rural women in Ethiopia say they are choosing smaller families to help them better deal with the negative effects of climate change. Women in Niger say that smaller families mean less competition for food during the lean season.

People concerned with humanity’s fate in the face of climate change should pay sharp attention to the words and actions of these women. Niger and Ethiopia are countries of the Sahel, the semi-arid southern border of the Sahara desert. During the 1970s and 1980s, this region suffered massive drought and famine—making the Sahel among the first places on Earth to be ravaged by human-induced climate change. Today, unprecedented population growth and intensifying cycles of drought are undermining the region’s food security and development. Yet for every woman in the region who currently uses contraception, three to four others want to space out or limit their childbearing but are not using contraception.

In the poorest countries, the net effect of slower population growth will likely be an increase in carbon emissions—economic conditions will improve and consumption will increase. And that’s okay. Meeting women’s contraceptive needs in least-developed, highest-fertility nations is a precursor for development that could help lift nearly 1 billion people out of desperate poverty. On a global level, meanwhile, achieving the medium UN population projection for the end of the century—as opposed to the high projection—would keep more than 7 billion tons of carbon per year out of the atmosphere.

Where the link between population and environment is concerned, too many heads have been buried in the sand. Because of tragic, coercive population programs that have sometimes been enacted in the past, even people who appreciate population’s impact on the environment can be afraid to attract criticism by expressing their views. National leaders need to escape this cloud of fear and clearly acknowledge that human beings have exceeded Earth’s carrying capacity. Influential people involved in development, natural resources, and of course climate must recognize that sustainable progress can’t be achieved until population is stabilized. Equally important is ensuring international investment, on a level commensurate with the world’s need, in voluntary family planning and in quality education for adolescent girls.

In the wake of the Paris climate conference, many individuals may be wringing their hands—feeling powerless in the face of global climate change. But there is one highly important contribution to the climate that high-consuming couples can make: considering their carbon legacies when they plan their families.

The original article was published in The Bulletin of the Atomic Scientists, and can be found here.