As countries move through their development phases, not only do they industrialize and institutionalize, they also urbanize-- an increasing proportion of their populations move from rural areas to urban centers. The notebook page reproduced below shows the global trend from 1850 through 2011 and the prediction for 2050. The page is based largely on data from the U.N. World Urbanization Prospects: The 2011 Revision.
I have seen some U. N. estimates for 2100 suggesting that by then 99% of humanity will live in urban areas.
This raises some interesting questions.
1. Will present urban areas simply grow larger to accommodate the increase?
2. Or, will new urban areas germinate to cover portions of the Earth's surface otherwise required either to supply resources to urban dwellers or to provide refuges for the wild?
3. Is there a tipping point between the demands of urban populations for vital resources (food, fuel, water, raw materials, etc.) and the ability of the non-urban areas to provide them? (Non-urban areas = croplands, rangelands, forests, wilderness, etc.)
An increasing global human population offers significant challenges; increasing urban (dependent) populations adds another dimension to these challenges.