Cities must address climate change. More than half of the world’s population is urban, and cities emit 75% of all carbon dioxide from energy use1. Meeting the target of the 2015 Paris climate agreement to keep warming well below 2° C above pre-industrial levels requires staying within a ‘carbon budget’ and emitting no more than around 800 gigatonnes of CO2 in total after 2017. Yet bringing the rest of the world up to the same infrastructure level as developed countries (those listed as Annex 1 to the Kyoto Protocol) by 2050 could take up to 350 gigatonnes of the remaining global carbon budget2. Much of this growth will be in cities in the developing world (see ‘Urban development challenge’).
Urban planners and decision-makers need evidence to help them manage risks and develop strategies for climate mitigation and adaptation. Scientists are increasingly thinking of cities as complex systems and working more closely with communities. New concepts are emerging, such as smart cities.