Travis and Sadiye Rieder read a book with their 2-year-old daughter, Sinem, in their Maryland home

You can drive an electric vehicle powered by rooftop solar panels, replace your old appliances and light bulbs with energy-sipping versions, recycle compulsively, compost, give up meat, eschew air travel, buy used-everything, make your own sandals out of old tires. You can do these and all sorts of other things in your personal quest to lower your carbon footprint. Doing so will indeed mitigate to some tiny degree the climate change that, despite the best efforts of the Intergovernmental Panel on Climate Change, is hurtling us into a slew of potentially catastrophic unknowns as this century steams ahead.

But if you truly care about the climate and the future of a human civilization that developed in the current temperature regime, you could do something that has a much bigger impact: have one less kid. Or more precisely, says Johns Hopkins University philosopher and bioethicist Travis Rieder, one-half less kid. (Those who have reared children would recommend the top, rather than the bottom, half). [more]