Urbanisation is a planetary scale change process. In the past 200 years, the proportion of the world's population living in cities has grown from about 5% to more than 50%.1 By 2050, about 2·5 billion additional people will need to be housed in cities—more than 1 million people every week—with about 90% of the increase concentrated in Asia and Africa.2 Urban land cover is expected to increase by more than 1 million km2 by 2030, nearly tripling the global urban land area circa 2000, threatening biodiversity and affecting ecosystem productivity through loss of habitat, biomass, and carbon storage.3.
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