Seven billion and 31 gigatons.

This editorial is adapted from a previous work by the author, “Seven Billion and 31 Gigatons: Making the Population–Climate Connection,” the author's presentation at Reproductive Health 2011, ARHP's annual clinical conference, and “Policy Review: Thoughts on Addressing Population and Climate Change in a Just and Ethical Manner,” which appeared in Population and Environment in 2009 and is cited throughout this editorial [1]. The United Nations announced last October that earth's population had passed 7 billion, the largest number the planet has ever seen [2]. Only 100 years ago, our planet held fewer than 2 billion people. Global population has doubled in my lifetime, from 3.5 billion in 1968 to 7 billion now. And we are on track to add 2 billion more by the year 2050 [2]. That is the equivalent of adding another China, United States, Brazil and Nigeria in less than 40 years. Media coverage of the 7-billion milestone was mostly somber, with images of crowded cities, belching smokestacks, denuded forests, starving children, polluted rivers and spreading deserts. Some looked at Japan and countries in Europe with declining populations, but that was also presented as bad news: aging people, strained social safety nets, shuttered schools, a dwindling work force — a “baby bust.” One forward-looking message that came through clearly in the discussions around 7 billion was that we must take better care of the environment if our children and grandchildren are to have sustainable lives. Indeed, while there may be disagreement about how to deal with a growing global population (see the June 2011 Contraception editorial [3]), we do seem to be moving toward a consensus that we really must do something about the strange and scary weather, in the form of monumental tornadoes, droughts, blizzards, extreme temperatures and floods, that we, no matter where we live on the planet, are facing. In other words, we must confront climate change. Climate change is happening. And scientists agree that it is generally caused by three factors: greenhouse gas emissions, economic growth that fuels energy consumption and population growth that fosters increased greenhouse gasemitting activities. In posing strategies to mitigate climate change, efforts have been geared primarily toward the first driver, specifi-