“Consumption-based footprinting” is a mouthful, but while it may not flow smoothly off the tongue, it’s an elegant concept — and an important way of looking at our problems.

A footprint, of course, is the measurement of the total impacts of a thing, be it a building, business, or ballgame. Consumption, of course, describes the things we use. So consumption-based footprinting is an attempt to measure the total impacts of everything we use. Boiled down: If we use it, its emissions are ours, no matter where the thing originated.

Now, footprinting is a bit of an arcane art. Because cities themselves are brain-boggling in their complexity, modeling the kinds and amounts of greenhouse gases their economies create represents a considerable task. It is not an impossible task, however, especially if what we’re seeking is a model good enough to guide decision-making, not a perfect reflection of reality.

In order to get our “good-enough” model, we need to know what it is we’re trying to measure — and this is where the disagreements really begin. Essentially, there are three camps, which we might think of as city-map footprinting, mailbox footprinting, and shopping-basket footprinting (though their technical descriptions are often geographic, production, and consumption footprinting, respectively).

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The city-map footprinters generally say we should measure those emissions created within a city, or created to directly power activities within a city: the oil burned in the cars we drive, the gas burned in our hot-water heaters, the coal burned in a nearby power plant to electrify the garage door, that sort of thing. This is the most common approach to footprinting, but its virtue is simplicity rather than accuracy.

The mailbox footprinters say we should measure all the emissions we ourselves produce. In other words, yes, we should include our cars, water heaters, and garage doors, but also the emissions our factories and workplaces create in the process of making the goods and services we export. This is a less common approach.

The shopping-basket footprinters say we should count all the emissions created by the things we use and consume, or created by the systems that support those things. So, yes, we should count our cars, water heaters, and garage doors, but also the roads on which those cars drive, the manufacturing plants that made those water heaters, and the mining and shipping operations that produced the coal burned to raise and lower those garage doors. Basically, this consumption-based approach says that if we use something and benefit from its use, we are responsible for all of the greenhouse gases it took to make that thing.

Even this can seem a bit complex, though, so I like to imagine that carbon emissions are cakes, and emissions-reductions are a diet. If we think of cakes and diets, we see that the three approaches like to count very different calories:

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  • Geographic footprinters say, “I will count only those cakes I both bake and eat at home.”
  • Production footprinters say, “I will count all the cakes I bake, whether I eat them or not.”
  • Consumption footprinters say, “I will count all the cakes I eat, no matter who bakes them.”

If what we care about is modifying our caloric intake (read: greenhouse gases), consumption-based footprinting is clearly the best approach. (For ethical reasons, we may also want to take a hard look at the kind and number of cakes we’re baking and sending elsewhere, but if we’re looking to lose weight … well, baker, heal thyself.)

Consumption-based footprinting helps us imagine carbon zero cities, because it gives us a truer sense of our climate impacts. In addition, it draws our attention to big systems. Looking at our lives, we begin to realize that large percentages of the greenhouse gases created in the process of housing ourselves, feeding ourselves, shopping, working, and getting around are emitted out of our sight or within systems not immediately amenable to change by individuals. We have a lot of work to do, and we cannot reach our emissions goals simply by tweaking the end product in a system — because most of our emissions come from the inner workings of the systems themselves.

This kind of understanding can be overwhelming, but also empowering: If we can see the systems that underpin our various ways of living, we can see, too, how changing those systems can produce large reductions in emissions patterns. Every city will be different, of course, having differently shaped carbon footprints and thus different systems-change priorities. But every city can use consumption-based footprinting to see its climate impacts more clearly and completely.

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