Salon.com: Condoms against climate change, by Andrew Leonard:

Thomas Malthus: Prophet of overpopulation doom, or the first family planner? 

From "Fewer Emitters, Lower Emissions, Less Cost: Reducing Future Carbon Emissions by Investing in Family Planning":

The historical relevance of Malthus'work in any family planning study cannot be understated. In fact,Richard Ehrman's "The Power of Numbers" states that Malthus' "call for'prudential restraint' — by which he meant later marriage — can besaid to have opened the way for family planning."

The "Fewer Emitters" study, written by the London School of Economics' Thomas Wire at the behest of the Optimum Population Trust, makes a fairly straightforward point. If all the women in the world who already want to avoid or postpone pregnancy weregiven access to contraceptives, there would be fewer babies, andeventually fewer greenhouse-gas emitting humans. 

This is a point thatis also made in an upcoming study soon to be published by the World Health Organization:"Runaway population growth in countries such as Ethiopia and Rwanda,"reports Bloomberg News, "where contraceptives are in short supply isexacerbating drought and straining fresh water supplies." The Optimum Population Trust goes one step further,however, by calculating the cost-benefit effectiveness of spendingdollars on family planning as opposed to the roll out of low-carbonenergy technologies. . . .