55 "don't succeed in solving them by our own actions"
Jared Diamond, "Malthus in Africa, Rwanda's Genocide," ch. 10 in Collapse: How Societies Choose to Fail or Succeed (New York: Viking, 2005).
56 run into a wall
"Groundwater Depletion Rate Accelerating Worldwide," ScienceDaily, September 23, 2010, http://www.sciencedaily.com/releases/2010/09/100923142503.htm.
57 "when the balloon bursts, untold anarchy"
Fred Pearce, "Asian Farmers Sucking the Continent Dry," New Scientist, August 2004.
58 capital city of Sana'a only one day in four
Lester Brown, "This Will Be the Arab World's Next Battle," Guardian, April 22, 2011.
59 declined more than 30 percent in the last four decades
Ibid.
60 "a hydrological basket case"
Ibid.
61 dramatically overminimize the future effects of choices
David Laibson, "Golden Eggs and Hyperbolic Discounting," Quarterly Journal of Economics 112 (May 1997): 44378.
62 more than 95 percent of the new additions will be in developing countries
United Nations Department of Economic and Social Affairs, "World Population Prospects: The 2010 Revision," 2011, http://esa.un.org/wpp/Documentation/pdf/WPP2010_Highlights.pdf.
63 global population will take place in cities
United Nations Department of Economic and Social Affairs, "World Urbanization Prospects: The 2011 Revision," March 2012, http://esa.un.org/unpd/wup/pdf/WUP2011_Highlights.pdf.
64 population of the world at the beginning of the 1990s
Ibid.; U.S. Census Bureau, "Total Midyear Population for the World: 19502050," http://www.census.gov/population/international/data/worldpop/table_population.php.
65 increased tenfold over the last forty years
United Nations Department of Economic and Social Affairs, "World Urbanization Prospects: The 2011 Revision."
66 see a reduction in their share of the world's urban population
Ibid.
67 no more than 15 percent of people ever lived in urban areas
Susan Thomas, "Urbanization as a Driver of Change," Arup Journal, 2008.
68 still only 13 percent at the beginning of the twentieth century
Sukkoo Kim, "Urbanization," The New Palgrave Dictionary of Economics (New York: Palgrave Macmillan, 2008); Thomas, "Urbanization as a Driver of Change."
69 for the first time, more than half of us lived in cities
United Nations Department of Economic and Social Affairs, "World Urbanization Prospects: The 2011 Revision."
70 64 percent of the population in less developed countries living in cities
Ibid.
71 in 2013, twenty-three cities will have more than that number