Urban climate change is a crossroads in two very different senses. One is historical. With the world now more than half urban, and given the ecological consequences of the world's high-consumption urban centers, we are at an ecological crossroad. We either head off the worst of ecological collapse through concerted and forward-looking action, or we face a 'Mad Max future' of dystopia, violence, and upheaval. The second crossroad is intellectual. Our individual disciplines are unable to grasp the magnitude of the economic-ecological challenges ahead. For that we need to work holistically,...