As we commemorate UN Earth Day this year, our planet is in something of a bind. Over the last century, the global population has, overall, grown vastly wealthier as our societies and technologies have developed at breakneck speed. But that development has come at a cost; we are beginning to onerously tax the environment in which we live. Meanwhile, the world has hardly reached a point where everyone is well off. An estimated 3 billion people—or just under half the world's population—live on less than $2.50 a day.