I'm one of those people who takes climate change seriously and who quietly does a lot of not-driving, and not-consuming, in order to reduce the amount of greenhouse gases I'm putting into the sky. I don't keep mathematical track of my use and impacts, I just refrain a lot.
By far the biggest thing I've done to lessen my impact on our planet home was back in 1971 when I decided that, given the mushrooming human population of the world, and seeing the corresponding increase in resource consumption and pollution, I decided, at the ripe age of 17, not to have offspring, kids of my own. And so it has been.
When we talk about a person's carbon footprint, shouldn't that include all future impacts by that person's offspring (and their offspring's offspring, etc.)? If we don't include offspring in the footprint measurement, then even if per capita greenhouse gas emissions decrease, total greenhouse gas emissions are likely to continue to rise. In plain English and because you have a choice about it, if you're still making and having babies, objectively-speaking you can't be very green, regardless of what else you may be doing or not doing. Reducing the size of the human population by not contributing to its continuing expansion, is, by contrast, very very green. Not having a baby makes a large and immediate difference compared to having one. It's conscious choice.
Neil