It has been my purpose in this book to describe the ways in which cities are altering their own climates and to consider what actions might contribute to a slowing of the rapid warming already underway in urban environments. The need for cities to actively manage the growing threat of extreme heat within their own jurisdictions has become ever more apparent during the period of the book's writing – a period in which cities around the world have experienced some of the most extreme climate-related events ever visited on human settlement. Yet, coupled with urban heat waves, droughts, flooding events, and tornadoes of unprecedented intensity in the past few years has been an almost complete breakdown of the international policy framework developed to manage the problem of climate change. In the wake of the pronounced failure of the Copenhagen Climate Conference to establish a successor agreement to the Kyoto Protocol, a growing list of developed nations have announced their intent to withdraw from the global policy framework altogether by the close of the first commitment period in 2012. These recent events in concert – a growing incidence of extreme weather in urban environments and a widening climate-policy vacuum – require cities to move more aggressively to protect their populations from climate-related threats in the present period.