Probably the single-most concrete and substantive thing an American, young American, could do to lower our carbon footprint is not turning off the lights or driving a Prius, it's having fewer kids. . . we'll soon see a market in baby-avoidance carbon credits similar to efforts to sell CO2 credits for avoiding deforestation.
The truth is, fish have very little sex life. If you have ever tried to make love under water, you will know why.