Cities are one of the greatest contributors and likely best opportunities for addressing climate change.[2] Cities are also one of the most vulnerable parts of the human society to the effects of climate change,[3] and likely one of the most important solutions for reducing the environmental impact of humans.[2][3] More than half of the world's population is in cities, consuming a large portion of food and goods produced outside of cities.[4] The UN projects that 68% of the world population will live in urban areas by 2050.[5] Hence, cities have a significant influence on construction and transportation—two of the key contributors to global warming emissions.[4] Moreover, because of processes that create climate conflict and climate refugees, city areas are expected to grow during the next several decades, stressing infrastructure and concentrating more impoverished peoples in cities.[6][7]