When Mr. Murtaugh runs the numbers, he finds some alarming results. Take an American woman who checks all the green boxes: She recycles, installs energy efficient windows, cuts back how much she drives, and so on. Yet simply by having two children, Prof. Murtaugh reports, she will add nearly 40 times the amount of carbon dioxide emissions she had saved with those lifestyle changes. No wonder the Los Angeles Times Web site reports on this study under the title “Tie Your Tubes and Save the Planet?”…

Maybe. But accept his assumptions, and it means that when a friend has a baby, you have to think we’re all the worse for it. It means that instead of celebrating the development that brings things like refrigeration, cars and calories to people who don’t now have them, we fear the day that a child in Manila enjoys enough of the blessings of life to have the same carbon footprint as a kid from Minnesota.

And if we really think the answer is below-replacement level fertility, it should mean taking a closer look at places such as Japan and Europe, where we can see what happens to societies when people stop having children.