The extent and rate of global environmental changes, whether greenhouse gas-induced warming, deforestation, desertification, or loss in biodiversity, are driven largely by the rapid growth of the Earth’s human population. Given the large and ever-increasing fraction of the world’s population living in cities, and the disproportionate share of resources used by these urban residents, especially in the global North, cities and their inhabitants are key drivers of global environmental change. Here attention is directed to the impact of cities on climate. The focus is not on the effects of cities on global-scale climate, rather the effects globally of cities at regional and local scales. Distinct urban climates at these scales have long been recognized (dating back to Howard 1833). Locally, they are of greater magnitude than projected global-scale climate change and enhance the vulnerability of urban residents to future global environmental change. Moreover, interventions at these scales have the potential to mitigate broader environmental change both directly and indirectly.