Urban Ecology, Part II

In the March-April 2000 issue of this newsletter (No. 362, page 8), I discussed three indicators--depletion, disturbance, and dependence--to characterize the environmental consequences of human activity, which Todd Wildermuth and I applied to an agricultural county in Kansas. The next step is to do the same analysis for an urban area. We already know that a city has high values of all three indicators, especially dependence. The latter has been vividly publicized in the ecological footprint concept.

These impacts of urban life are accepted enough to justify trying to reduce them. Planning (both formal--what professional planners do--and informal) has goals that communities foster and embrace. In particular, the cities of Champaign and Urbana, IL, are updating their comprehensive plans. Rumi Shammin and I are starting a project to determine how the measures in the Champaign-Urbana comprehensive plans stand up against biophysically based indicators of sustainability.

One thing we have learned so far concerns sprawl: sprawl issues have large energy implications. We were skeptical because previous work had shown that at least half of the energy required to support the consumption pattern of an American household results from purchases other than auto fuel or residential heat and light. This fraction is even higher for the more affluent who tend to live in the sprawling suburbs. On the other hand, the standard image of sprawl is of people in bigger houses on larger lots at greater distances from work and cultural areas driving more and bigger vehicles over those longer distances. Therefore, we have taken a closer look.

Our approach fits under the general heading of "energy cost of living." Research over 30 years has produced "energy intensities" for a wide range of consumer goods and services; that is, the energy necessary for the production economy to provide one unit of a good or service for final consumption. Determining the intensities often involves use of economic databases, and the intensities are measured in energy units per dollar. For example, for the entire U.S. economy, intensity ~ 10,000 Btu (British thermal unit) per dollar. (10,000 Btu is the energy content of about 3/4 lb. coal or 2/3 qt. gasoline.) Intensity varies from commodity to commodity: 9,000 Btu/$ for food at home; 5,400 for housing; 20,000 for public transportation; and 115,000 for auto fuel. These intensities can be combined with details of consumers' expenditure patterns to yield the energy cost of living.

Figure 1a shows the expenditure pattern (in 1999 dollars per year) for an average household. Figure1b shows this market basket converted to its energy requirements. In dollar terms, residential fuel and energy are only 5% of the pie, while in energy terms the fraction has jumped to 44%. Figure 2 shows the energy pies for three different expenditure levels. The direct fraction varies from 56% for the lowest expenditure decile to 33% for the highest.

Of the 15 expenditure categories, 4 can be said to be sprawl-dependent: housing, residential energy, gasoline and motor oil, and auto purchase and maintenance. Their sum ranges from 72% for the lowest decile to 53% for the highest. Thus over half of the total energy impact comes from these four categories that have most to do with sprawl.

The upshot is that the sprawl-energy connection indeed seems strong even when one is sensitive to the inevitable energy impact of every purchase. Admittedly, this is all very simplified. Among other problems, this analysis assumes that a car that costs twice as much requires twice as much energy to produce, which cannot be exactly right. In addition, one can ask what an "unsprawled" household would do with the money it could save by driving less to and from a smaller, less energy-craving house. If it is spent on fuel for a private airplane, not much energy reduction would result. If it is spent on plane tickets for a trip to Reno, some energy is saved. If it is spent on concert tickets, more energy is saved (the more service-intensive an activity, generally speaking, the less energy per dollar).

This exercise shows that sprawl-related expenditures have significant energy consequences, but also that household energy demand is a consequence of total consumption. Sprawl is usually thought of as a density issue (an intensive quantity), while we see that energy impact has both intensive and extensive aspects. This leads us to ask "Is the problem sprawl (intensive), or is it overall growth (extensive)?" Another way to put this is to compare "efficiency" and overall "scale" in environmental analysis. We will pursue this question in our study of local cities.

Robert A. Herendeen, Center for Aquatic Ecology

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