A beggar and his child look for donations from migrants returning home on an overpass that leads to the train station in Beijing, China.
While the sustainable part of this year's U.N. Conference on Sustainable Development is getting most of the attention, development is just as important. The single biggest contributor to ill health — and to an extent, environmental destruction — is poverty. The poverty of the very poor in places like the Brazilian Amazon and Madagascar helps drive the destruction of forests and other wildlife habitats. Global poverty has fallen significantly since the first Rio summit 20 years ago, thanks largely to development in countries like China and India, but too many other nations have been left behind. Now with the global economy teetering, we need to double down on development — and ensure that it's sustainable at the same time.