Essays on Science and Society

The Urban Challenge

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Science  15 Jun 2012:
Vol. 336, Issue 6087, pp. 1396-1397
DOI: 10.1126/science.1223952

“The Urban Challenge” was a chapter in the 1987 Brundtland report, Our Common Future. The issues remain depressingly familiar for Rio+20. Urbanization has continued around the world, sometimes diminishing rather than enhancing social and environmental capital. Urban populations then 2 billion are estimated to have reached 3.5 billion. But three unforeseen new factors have changed the world's urban landscape since the 1980s: globalization of transportation, information technology, and clean energy. Globalization could only have taken place with adaption of cities (and their ports) on a scale without precedence. Driving that change have been leaps in logistics and transport technology. Modern cities have become inseparable from the means with which they link to each other. The scale of production and consumption in modern cities is awesome, not least for the problems created in waste and pollution. At the heart of these issues is continued availability of clean energy that is affordable for all and less dependent on fossil fuel. The race is on to reconfigure urban processes and land-use patterns to extract the most from waste streams of matter and energy and to minimize the resource overhead of transport.


Finding optimal solutions for the complexity of the growing modern city is beyond the reach of conventional pencil-and-paper city master planning. Cities are turning to increasingly sophisticated software decision-support tools both to minimize internal transportation needs and to optimize the locational opportunity to recover high-grade waste energy and material flows to lower-grade uses. At the moment, even the powerful optimizers used in process industries are hard pressed to tackle the formidable “integer programming” problem presented by the myriad of possible networks of resource flows of a modern city.

Nevertheless, the prospect is a possible halving of primary resource use, and it will have to be achieved. One study of global data for cities sounds the warning; as urban population grows, major innovation cycles have had to be generated at a continually accelerating rate to sustain growth and so avoid stagnation or collapse. The urban citizen is running with no time to take breath.

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