More than 200 million women worldwide want contraceptives, but don't have access to them, according to an editorial published in the British medical journal, Lancet. That results in 76 million unintended pregnancies every year.

If those women had access to free condoms or other birth control methods, that could slow rates of population growth, possibly easing the pressure on the environment, the editors say.

"There is now an emerging debate and interest about the links between population dynamics, sexual and reproductive health and rights, and climate change," the commentary says.

In countries with access to condoms and other contraceptives, average family sizes tend to fall significantly within a generation. Until recently, many US-funded health programs did not pay for or encourage condom use in poor countries, even to fight diseases such as AIDS.

The world's population is projected to jump to 9 billion by 2050, with more than 90 per cent of that growth coming from developing countries.

It's not the first time lifestyle issues have been tied to the battle against global warming. Climate change experts have previously recommended that people cut their meat intake to slow global warming by reducing the numbers of animals using the world's resources.