Demographers are not as worried today as they were several decades ago about the prospect of a "population bomb," a scenario where so many people come to populate the planet that we exhaust its resources. Population growth has slowed in many parts of the world. And in much of North America, Europe, China, and Brazil, fertility rates are so low that local populations are on pace to decline.
These trends, however, don't cover the whole story of human impact on the environment. The growth in the number of humans on earth may be slowing. But something very different is happening in the growth of human households.