Blockading urban sprawl may not be the answer either. Allowing for the same population growth without urbanization might have even more severe environmental consequences, as subsistence farming expands, enmeshing residents in chronic and crippling poverty. If urbanization fails in developing regions, whether in Africa or the Indian subcontinent, the world could see continued migrations to London, Los Angeles and other developed world megacities, suggests physicist Luis Bettencourt of the Sante Fe Institute, who studies urbanization issues. Indeed, Seto and her colleague's modeling suggests that cities in North America will nearly double their real estate by 2030.
The next 20 years or so represent a window of opportunity to learn how to grow. Seto, for her part, suggests more research is needed on "what types of urbanization minimize negative environmental and social impacts and how do they emerge?" Her group plans to continue its work by projecting global density of population—a key metric for minimizing environmental impacts. In addition, the world will need to avoid the kind of infrastructure lock-in—from coal-fired power plants that produce cheap electricity but also pollute to living and working areas separated by vast distances requiring energy-intensive commutes—that has characterized the first century of rapid urbanization. Some estimates suggest that as much as $30 trillion in infrastructure investments will be made to support such urbanization by 2030.
Of course, as Bettencourt observes: "Cities were never formed and have never grown with the objective of saving energy or protecting the environment." Yet, cities often serve that purpose by default. One of the defining features of slums is densely packed inhabitants, and more developed city areas often boast high land values that then encourage tall buildings also densely packed with people and businesses, which further encourage walking or mass transit. "This is how larger cities manage to do more with less," he adds, suggesting that such opportunities should be "consciously and systematically seized as development happens."