Cities may be our last best hope in the epic battle against an increasingly disruptive climate. The lower birth rates of urban dwellers help reverse a huge and growing global population. Because cities are heating up twice as fast as their hinterlands, four strategies to address urban heat islands are presented. Architecture and urban design can play a critically important role in averting – or at least slowing – the climate and overpopulation crises, as humanity tries to rally for a sustainable planet.