Increased access to contraceptives could slow population growth and curtail climate change, according to an editorial published in The Lancet medical journal on Friday.

But two hundred million women in the world who want birth control can’t get it, resulting in 76 million unwanted pregnancies every year.

Leo Bryant, a researcher at the World Health Organization who wrote the editorial, led the study on the relationship between climate change and population growth in the world’s 40 poorest countries. Rapid growth puts demographic pressure on the environment in almost all of them, but only six countries have proposed plans to address the problem.

While population growth in poor nations with low carbon emissions is unlikely to increase global warming significantly, Bryant said overpopulation combined with climate change will worsen living conditions and degrade natural resources.

The average family size, though, shrinks dramatically during a generation in most countries with regular access to birth control, Bryant said.

A case study in Ethiopia that trained people in sustainable land management practices and increased family planning availability saw an immediate improvement to the environment. What’s more, a new UK report, “Few Emitters, Lower Emissions, Less Cost,” found family planning is five times cheaper than traditional green technologies to fight climate change. Every $7 spent on basic family planning during the next four years would reduce global CO2 emissions by more than 1 tonne.

The International Conference on Population and Development Programme of Action consensus in Cairo called universal education and sexual reproductive health care and rights paramount to sustainable development in 1994. Despite some successes, writes Bryant, “a deplorable lack of financial investment and political will has dominated the inertia in the past 15 years.”

Policymakers will neglect family planning to avoid being associated with extreme measures like one-child policy in China, which, since its introduction, reduced the fertility rate from more than three births per woman to approximately 1.8.

“We are certainly not advocating that governments should start telling people how many children they can have,” Bryant told Reuters. “The ability to choose your family size… is a fundamental human right. But lack of access to family planning means millions of people in developing countries don’t have that right.”

The study will be published in the WHO Bulletin in November, a month before the Climate Conference in Copenhagen, which Bryant hopes will provide a forum to discuss a “more human-based, rights-based adaptation approach” to climate change.

“Such a strategy would better serve the range of issues pivotal to improving the health of women worldwide.”