More children equal more carbon dioxide emissions. And recent research has resulted in renewed coverage of the notion that one of the cheapest ways to curb emissions in coming decades would be to provide access to birth control for tens of millions of women around the world who say they desire it. A study by researchers at the London School of Economics and commissioned by the Optimum Population Trust came to the following conclusion:

Contraception is ‘Greenest’ Technology U.N. data suggest that meeting unmet need for family planning would reduce unintended births by 72 per cent, reducing projected world population in 2050 by half a billion to 8.64 billion. Between 2010 and 2050 12 billion fewer “people-years” would be lived – 326 billion against 338 billion under current projections. The 34 gigatons of CO2 saved in this way would cost $220 billion – roughly $7 a ton [metric tons]. However, the same CO2 saving would cost over $1trillion if low-carbon technologies were used. (Here’s a link to a pdf of the report.)

I recently raised the question of whether this means we’ll soon see a market in baby-avoidance carbon credits similar to efforts to sell CO2 credits for avoiding deforestation. This is purely a thought experiment, not a proposal. But the issue is one that is rarely discussed in climate treaty talks or in debates over United States climate legislation. If anything, the population-climate question is more pressing in the United States than in developing countries, given the high per-capita carbon dioxide emissions here and the rate of population growth. If giving women a way to limit family size is such a cheap win for emissions, why isn’t it in the mix?

A related story from the archives.