Up Stream Solutions (Way up Stream)
The cheapest way to reduce carbon in the atmosphere is by providing birth control methods for women who want them. $7 contributed toward the purchase of contraceptives (and instructions on how to use them effectively) can prevent the emission of one ton of atmospheric carbon dioxide. This compares to approximately $32 per ton for renewable energy sources such as wind and solar. You can read about the study by the London School of Economics at:
http://www.popsci.com/environment/article/2009-09/contraception-cheapest-way-curb-carbon-dioxide