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Suburban sprawl image via sutterstock. Reproduced at with permission.

While densely-populated cities produce less greenhouse gas emissions per person, the suburban sprawl around these cities — and the increased driving, bigger homes, and higher emissions from goods and services that accompany suburban living — essentially cancels out that benefit, according to new research from the University of California at Berkeley.

“While many cities in the country have taken on very impressive programs to reduce greenhouse gas emissions … often the suburbs get left out of that equation,” said Daniel Kammen, professor at Berkeley’s Goldman School of Public Policy and director of the Renewable and Appropriate Energy Laboratory in an interview with ClimateProgress. “That commuting footprint, not just of physically commuting but of the goods and services delivered to suburbanites, has a big effect and in fact, it really undoes a lot of the gains made by that dense urban core.”

The study analyzed 37 individual categories, including weather, electricity supply, and the emissions embedded in food and other goods and services, to provide a much more complete picture of household carbon footprints across the country. They found that on average, suburbs account for half of all household greenhouse gas emissions, even though they account for less than half of the population.

“The average [household carbon footprint] in an urban core in the country is about 50 percent less than the average in the commuting suburbs around it, largely because of transportation and bigger homes in the suburbs,” Kammen said.

Using this model, researchers determined the size and composition of the household carbon footprint for essentially every zip code, state, city, and county in the U.S. and organized all of the data into an interactive map.

Providing a complete picture of greenhouse gas emissions was a key motivator in undertaking the research, said Kammen. While reducing emissions from vehicles and electricity use are common solutions to addressing climate change, there are other sources of greenhouse gas emissions that are harder to quantify and thus address. A good example is California’s greenhouse gas law, A.B. 32. The law is all-inclusive, meaning it includes not only the emissions that stem from electricity use, but transportation and goods and services, as well.

“So while we’ve made a lot of progress in California on our clean electricity standard … we’re much further behind on the carbon embedded in the rest of our goods and services combined,” said Kammen.

Additionally, the researchers wanted to look at the bigger picture of emissions beyond just the urban core. Kammen and co-author Christopher Jones found that the primary drivers of carbon footprints are household income, vehicle ownership and home size — all of which are considerably higher in suburbs.

“When you look at the map, urban areas really look like … a hurricane, because it’s a green low-carbon core surrounded by a lot of red on the map, a lot of high-carbon households,” said Kammen.

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A CoolClimate map of Washington, DC shows a pattern typical of large metropolitan areas: low-carbon areas (green) in the urban core with high-carbon areas (orange and red) in surrounding suburbs.

So is the solution to increase population density? Not so fast. Increasing population density in central cities “would require a really extraordinary transformation for very little benefit, and high carbon suburbanization would result as a side effect,” said Jones.

“This is not to condemn urban suburbs and just packing yourself in urban cores is a good thing,” Kammen explained. “We have cities that are relatively spread out — for example, Portland, Oregon, which has one of the best public transportation systems in the country and, as a result, Portland actually has the lowest per capita vehicle ownership of any big city.”

Portland is a prime example of the emissions reduction benefit that results from thinking through transportation policies, said Kammen. So even if you live in the suburbs, its convenient to get to work in downtown Portland using public transportation. It may not come as a big surprise but the Berkeley analysis confirms that public transportation can have a big impact. “Well-working mass transit systems not only allow you to bring down the carbon footprint but we know that places where mass transit works well are cities that are seen as more equitable and more livable for lower income people.”

Ultimately, Kammen emphasizes that there is no one-size-fits-all solution. In addition to population density, other important factors in measuring the household carbon footprint include the carbon-intensity of electricity production, energy prices, and weather and those factors vary considerably across the U.S. In California, for example, motor vehicles account for 30 percent of household carbon footprints, while just six percent comes from electricity. In areas that rely heavily on coal-fired power plants to meet their electricity needs, such as the Midwest and much of the South, that number is significantly higher.

While the most effective set of policies will vary across the country, the real lesson is that cities need to take a holistic approach as they tailor their greenhouse gas emissions reduction strategies. “Places in the country that have developed holistic pictures do much better, and by that I mean, it’s not just do I live in a home that has solar panels on the roof and then use mass transit, but everything I purchase comes to me and there’s carbon associated with that,” said Kammen.

In California, many cities are developing carbon budgets in an attempt to identify and address some of the more complex sources of greenhouse gas emissions. Kammen and Jones run a program that seeks to identify the California cities with the lowest carbon footprint per capita and found that the municipalities that pursue an integrated approach have the most success. “In the near-term we need these integrated policies and in the long-term, we need these policies plus cap-and-trade with a significant carbon price, but you can’t rely on one — things come and go,” Kammen explained.

By providing tools that enable people to easily calculate their own carbon footprint and then compare that with the average household carbon footprint in their area, Kammen and Jones hope to empower people to make adjustments to their carbon footprint and take action to address climate change, in addition to cities and states. “People need to act within their own spheres of influence, where they feel they can make the most difference,” Jones said. “We hope the information provided in these tools will help individuals, organizations and cities understand what makes the most impact locally and to enable more tailored climate strategies.”

The next steps for Kammen and Jones? First, adding even more detail to their model to better understand the impact of individual actions. “Right now crate and shipping is the fastest-growing component of emissions … energy use for homes hasn’t been growing that much because we’re somewhat close to the recession but everyone is doing e-shopping and things, so we want to understand that footprint.” And second, taking their model internationally. “A lot of goods produced in China are consumed in the U.S. and so while the actual greenhouse gas emissions for the iPhone I’m talking to you on took place in China where it was built, I’m using it here, so really those emissions are part of my embedded footprint here.”