Peak Urbanism, Future Cities and Climate
Over half the global population is already urban, and the UN expect this share to continue rising [[UN 2014]] (http://esa.un.org/unpd/wup/default.aspx). Not only are cities already responsible for about 70% of global CO2, but their concentration of population and infrastructure make them especially vulnerable to climate change. Unless serious mitigation actions are implemented, by 2100 the world average surface temperature could warm by 4 °C or more above pre-industrial. Cities would then be subject to a variety of biophysical hazards. Health risks would rise from both more frequent and more intense heat waves, and possibly, the spread of infectious diseases. Flooding risk would increase for many cities due to rising sea levels for coastal cities and/or hinterland river flooding. Adaptation limits would be reached, with the residents of the world’s urban slums suffering the most [[Moriarty and Honnery 2015]] (http://dx.doi.org/10.1016/j.futures.2014.12.009).
Alternatively, if timely and stringent mitigation policies are implemented, the changes to urban economies are likely to be profound, probably necessitating declining energy and material throughputs, even if resource constraints are not limiting. If so, the attraction of cities could lessen. So, whether the world adopts adaptation or mitigation, peak urbanism is likely in the coming decades.