Not having a child is the most environmentally responsible act one can do. For each child you don't have, you offset tens of thousands of tons of CO2 emissions, millions of gallons of water used, tons of trash produced, etc.
I've been kicking around starting a non-profit that pays people not to have children, with the funding coming from carbon credits.
"By first year itself an American toddler would have generated more Carbon dioxide emission than an average person in Tanzania will generate in a life time."
http://www.nationalgeographic.com/xpeditions/lessons/14/g68/...
http://www.greencontributor.com/index.php/human-foot-print.h...