Cities today must deal with growing stress on raw material supplies. Extraction of metals, minerals, and fuels is increasingly complex now that the easiest sources have been tapped. As a consequence, researchers and activists regularly call for materials efficiency and conservation, even advocating for “circular economies” in which goods and materials of all kinds are designed for comprehensive reuse or recycling. Increasingly, city leaders will be pressed to build urban economies that do more with less.
City-level data on materials consumption are sketchy and incomplete, but data at the national level give a sense of consumption in rich and poor countries and may be roughly indicative of urban consumption, given that cities consume some 75 percent of all natural resources. Materials flow analysis reveals interesting patterns that city leaders may want to be aware of. On average, each human being consumed 10 tons of materials in 2009, a 25 percent increase over 1980. (See Table 3–2; note that the high rates of contraction for Europe and North America are largely a function of the end year of the analysis, 2009, the first full year of the Great Recession.)11
But averages obscure: per capita consumption is 60 times higher in the highest-consuming country than in the lowest-consuming one. This differential suggests that, as poor countries continue to prosper, consumption levels are likely to increase greatly, and global materials use—and the environmental burden it brings—could surge. In an illustrative example, the people of Taipei, Taiwan, consume 30 kilograms of copper per person, with consumption growing at 26 percent per year, whereas residents of Vienna use 180 kilograms per person, at a growth rate of just 2 percent per year. As cities in poor countries prosper, the challenge is for wealthy countries to create the environmental and resource space needed for poor cities to prosper, and for poor cities to provide dignified lives to residents on a moderate materials budget.12
As city leaders consider how to dampen the appetite for materials, scientific insights suggest that city development may be influenced by a set of predictable, although bendable, relationships. A team of researchers interested in applying scaling laws to urban development has used data covering hundreds of cities from all continents to identify three sets of relationships that they say apply across myriad cities, cultures, and historical periods:
- For infrastructure, cities tend toward efficiency as they grow. A doubling of population size tends to produce only an 85 percent increase in sewer lines, power lines, roads, and other infrastructure.13
- For human needs—measured, for example, by employment, water consumption,
electricity consumption, and housing—a doubling of population leads to a doubling of these indicators, a 1:1 relationship.14
- For socioeconomic measures—including information, innovation, and wealth,but also serious crime and disease—a doubling of population produces roughly a 115 percent increase in these measures, or a 15 percent increase per capita.15
This analysis suggests that many urban development variables unfold within roughly a 15 percent variance (above or below) of population growth. Deviations from the 15 percent rule can be viewed as measures of over- or underperformance relative to the expectations for a city’s size. Researchers Luis Bettencourt and Geoffrey West note that relatively large deviations (as much as 30 percent) are found for city phenomena with small values, such as number of patents or number of murders, whereas economic variables often have much smaller deviations—less than 10 percent. These insights offer rough benchmarks to city leaders seeking to evaluate their performance relative to cities of similar sizes. But the benchmarks are not sustainability metrics; a city may perform better than similar-sized cities yet still be far from sustainable.16
Some scaling-laws analysts hypothesize that these urban dynamics emerge from the networks of connections found in cities, and that these connections are a function of density. Density drives connectedness, which drives innovation, which in turn drives the dynamics of urban development. But they worry that innovations in cities must occur at an increasing rate to support continued growth, and that, without increasingly rapid innovations, the indicators of urban advance could slow or stop. Their thinking has emerged within the past decade, and it remains to be seen how critical the role of continuous innovation is in urban prosperity.17
One of the many disadvantages of the linear, use-and-discard pattern of materials use—the model for most industrial economies—is their large streams of waste, much of which ends up in cities. Waste comes in many forms, including municipal solid waste (MSW, or garbage), construction and demolition waste, hazardous waste, and other streams. Data on waste volumes often are scarce or unreliable, but a World Bank study on MSW shows that the volume is huge and growing—and at a faster rate than urbanization. The study also shows that waste generation correlates with affluence, with a nearly fivefold difference in average waste generation per person between the world’s richest and poorest regions. (See Table 3–3 and Chapter 13.)18
The World Bank study projects that waste levels will increase 69 percent by 2025 over 2012 levels. Other scholars, using growth in income and population projections for various world regions, have projected that the peak in global waste production, under business-as-usual conditions, will not occur before 2100. With more aggressive sustainability policies, the peak could occur around 2075 and could be reduced in intensity by some 30 percent. The projections depend heavily on how waste generation unfolds in sub-Saharan Africa, a region with high population growth rates.19
Policies can make a big difference. New Yorkers produce some 1.49 tons of MSW on average, while a Londoner generates only 0.32 tons per capita, about a fifth as much, in part because of a landfill tax in the United Kingdom. The tax reduced the share of waste landfilled in the country from 80 percent in 2001 to 49 percent in 2010. City leaders will need to consider a wide range of policies to re-engineer their economies away from waste and toward recycling and reuse. (See Chapter 12.)20
Despite greater awareness of the need for materials to circulate more broadly, no economy is close to being circular yet. A 2011 study of 60 metals found that, at the global level, only 18 metals had an end-of-life recycling rate (the share of discarded metal that is recycled) exceeding 50 percent. And the United Nations Environment Programme reports that, of the metals found in the 50 million tons of electronic waste produced annually around the world, only 15–20 million tons is recycled.21
Gary Gardner is director of publications at the Worldwatch Institute and co-director of the State of the World project.
Read more in State of the World: Can a City Be Sustainable?