Energy-hungry suburbs eat up urban savings

The exceptions: the suburbs of New York and LA.

It may look idyllic, but it's remarkably inefficient. Credit: Oak Ridge National Lab

With climate change looming large on the horizon, a lot of effort has gone into pinpointing the biggest producers of carbon dioxide and other greenhouse gases. Now, a new study has identified a major culprit: suburbia.

The study, published last week in the journal Environmental Science and Technology, estimates household emissions across more than 31,000 ZIP codes to examine how carbon footprints vary across the United States. The researchers used a wide range of data to determine energy use, including population density (from US Census information), energy prices (based on data from the Energy Information Administration), daily temperature (via NOAA weather stations), and diet information (from the USDA nutrition database). Once the researchers had estimates for energy demand, they were able to calculate the household emissions resulting from this consumption.

Using data from the study, the researchers created a website where you can check out the average annual household carbon footprint in your ZIP code and estimate your own emissions.

Previous research had found a simple positive relationship between household carbon footprints and population density: as population density increases, average emissions decrease. But the new study suggests that the relationship between population density and energy consumption is a bit more complicated.

It’s true that as population density increases, household emissions rise—because denser-populated areas are generally wealthier, with larger houses, swankier vehicles, and longer commutes. But at a certain threshold (which turns out to be about 3,000 people per square mile) this relationship reverses, and average emissions actually decrease as population density continues to rise. Because space is at a premium in urban cores, city-dwellers tend to live in small apartments rather than sprawling homes and use public transit rather than gas-guzzling SUVs, greatly limiting emissions in very dense areas.

So the areas with the largest carbon footprints, it turns out, are suburbs. Energy use there is surprisingly high: the study estimates that household energy consumption in the suburbs is about 25 percent higher than in city centers. According to the authors, suburban emissions account for about half of all US contributions to climate change. In fact, the energy consumption in suburbia is so high that it actually cancels out any energy conserved by those living in densely populated urban cores.

There were two exceptions to this pattern: Los Angeles and New York, the nation’s two largest cities. Even when suburbs were included, average household emissions in these urban areas were relatively low, suggesting that very large cities may have net energy savings despite their suburbs.

There were also major differences in the energy consumption of different geographical areas. The Midwest and the Northeast, for example, consumed a disproportionately high amount of energy compared to other regions. Whereas the Midwest uses more coal-based electricity than other areas, California’s transportation-related emissions are exceedingly large.

However, the study is based on a range of assumptions, including relative uniformity within ZIP codes. In a single ZIP code, household diets, vehicle fuel economy, and home sizes certainly vary. The model also doesn’t account for mixed-use areas or places where residential and commercial or industrial zones are side by side.

But the findings are still potentially very useful in terms of energy policy. First, it’s clear that strategies to reduce emissions should focus on suburbs, where average household consumption is the highest. These areas should be the prime targets for programs pushing energy efficiency, solar power, and electric vehicles. Additionally, different policies may be needed in different geographical regions, since energy use patterns differ significantly across the US. Finally, it’s possible that some of these patterns hold true internationally and could be used to drive policy in areas where energy consumption data is unavailable. However, similar studies in other countries are needed to determine whether any of this information can be generalized.

If you live in the suburbs, it might be time to take another look at your energy consumption; you don’t want your urban neighbors starting to resent your Yeti-sized carbon footprint.

Environmental Science and Technology , 2013. DOI: http://dx.doi.org/10.1021/es4034364 (About DOIs).