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Blame their big houses and outsized driving habits.

You probably don't need a sophisticated climate model to tell you that a compact, car-free apartment in the city has a smaller carbon footprint than a 3,000 square-foot single-family house in the suburbs. But add all of those big, far-flung homes together, and their cumulative impact starts to look really disproportionate. In many metropolitan areas, this means that a narrow slice of households are responsible for a vastly larger share of the region's greenhouse gas emissions.

Just how much larger are we talking? An interesting new study out of Switzerland, published in the American Chemical Society's journal Environmental Science & Technology, looked at this question in a single town there. Researchers at ETH-Zurich developed a model using census data for the life-cycle assessment of housing and local transportation consumption in the town of Wattwil, home to 3,238 households. Twenty-one percent of the households there, the researchers calculated, were responsible for 50 percent of the region's housing and mobility-related emissions.

The main culprits? Large homes requiring a lot of energy to heat and cool, and relatively long commutes. This snapshot of a small town in Switzerland obviously doesn't translate directly to New York City (the authors also did not factor into their model other kinds of consumption, like food and clothing). But previous statistics from the U.S. suggest that the paper's main conclusion likely applies broadly: "The findings," the authors write, "suggest that [greenhouse gases] are not emitted equally."

This chart from the paper illustrates just what this pattern in Wattwil looks like:

"Housing and Mobility Demands of Individual Households and their Life Cycle Assessment," by D. Saner et. al, in Environmental Science & Technology.

Every household in town is shown on the x-axis, ranked according to combined emissions induced by housing (yellow) and transportation (green) consumption. The red dotted slope illustrates the cumulative share of emissions as a percentage of the entire town's footprint. Half of the households, or the 1,619 to the left, are together responsible for just 20 percent of all emissions. Meanwhile, about 21 percent of the households – those shown at far right – are responsible for half the emissions.

For the statistical-minded who are familiar with metrics of more traditional kinds of inequality, the researchers have calculated a Gini coefficient for the town's inequality of emissions (if the Gini coefficient were 0, every household in town would be producing the same emissions). Separately, the Gini coefficient for mobility emissions(0.64) is higher than that for housing (0.49). "This means," the authors write, "that housing impacts are more equally distributed among households than mobility impacts."

There's a positive way to look at all of this: When a few households are responsible for a disproportionate share of emissions, that means behavioral or technological changes within just a few households can also have an outsized impact on an entire town's carbon footprint. Cut the emissions of that 21 percent of households in Wattwil by half, the study concludes, and the whole community's housing and mobility emissions would fall by a quarter. That's without anyone else doing much of anything.

Top image: jason cox/Shutterstock.com

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