Every one of us contributes to the destruction of Earth's environment. We all consume resources and generate waste. One way to quantify each individual's impact on the environment is called a "carbon footprint" (you can measure yours here). Americans' carbon footprints hugely exceed the international average.
Some people who choose not to have children cite preserving the environment as a reason for their decision. Personally I consider it more of a free gift with purchase -- I chose not to have kids because I didn't want kids, and as a bonus I am not creating more Americans to add pressure to our environment.
Two conservationists wrote about their family planning decisions -- one had children and the other did not -- in Earth Island Journal. Erica Gies, who chose not to reproduce, wrote that "The health of the natural systems upon which we depend is declining. That decline is part of why I’ve decided not to have kids. I simply can’t in good conscience contribute to the rapid diminishment of our world. Also, given the degradation of natural resources and landscapes, children born today are likely to have a lesser quality of life than I am enjoying. I don’t want to condemn them to that."
Unsurprisingly I think she got the best of the mother, Julie Zickefoose, who wrote that she had children because "A thoughtful person’s child is not going to cause the poles to melt" because thoughtful people's children will be conscientious about their impact on the planet. Even so, they will have an impact.
Plus, as Gies argues, "kids have an uncanny ability to grow up to be their own people, who don’t necessarily live by your values or have the number of kids you’d prefer." A parent's thoughtfulness is no guarantee that her child will think the same way.
We don't often discuss the environmental consequences of our family planning decisions, so I recommend reading these two essays. Feel free to comment on this post to add your own perspective to the discussion.
On a side note, Zickefoose wrote that she didn't have children earlier than her late 30's because she was afraid -- "Afraid to add to the world’s masses. Afraid to give up my freedom to travel or do whatever I wanted. Afraid I wouldn’t be up to the challenge of raising good people. Afraid I’d let them down." Lest readers extrapolate her fear to all childfree adults, my own experience has been that it takes courage to be true to oneself against the tide of what I have called the "preachers of parenthood." Gies's experience sounds similar -- like me, she has been told that she was "selfish" for not having children. Her retort, that "My not having kids is an act of generosity that leaves more resources for his children," is better than anything I've come up with.