Where should you live to most reduce your carbon footprint? It seems obvious that city life with smaller homes, mass transportation, and easy access to shops and restaurants is preferable to the suburbs with its cars and bigger homes. But how about the benefits of rural areas where people grow their food and live closer to the land? What about regional climate, income and energy price differences?
A recent analysis by Jones and Kammen (2013) explored these questions at a national scale using a series of questionnaires and other available data sources. They took into account energy prices, heating fuel type, structure of homes, demographic information, number of vehicles owned, gas prices, population density, density of food establishments, travel patterns, local climate, diets and several other factors. They then used an input-output life cycle assessment to calculate greenhouse gas emissions.
Using this method they were able to create national maps highlighting the contributions from housing, transportation, food, services and other goods to get average household greenhouse gas emissions. Overall, household greenhouse gas emissions were highest in the Midwest, Northeast, parts of the South and the West Coast.
Interestingly, they found that household greenhouse gas emissions actually increase with population density up to a threshold of around 3000 persons per square mile. Above this threshold, average emissions decreased. Metropolitan areas have overall higher average household greenhouse gas emissions, which is largely due to the contribution of suburbs. Metropolitan areas tend to have rings of high household emission suburbs with low emission city centers. In fact, the zip codes with the highest emissions nationally were found in bands 15-45 miles from urban centers. Transportation was the primary reason for the unsustainable suburbs as well as their relatively high income and household size.
The researchers found that the most important variables included the number of vehicles per household, income, carbon intensity of electricity production, number of rooms and persons in households and population density. Less important variables included commute time, fuel prices, local climate and the year the homes were built.
These results have important policy implications: regional differences require something other than a one-size-fits-all carbon management strategy. For instance, regions with high electricity-related emissions should focus on finding cleaner sources of energy while suburban areas should focus on home energy efficiency upgrades.
For readers who are interested the authors have created an interactive webpage that allows you to estimate your carbon footprint, encourage sustainability and save money (http://coolclimate.berkeley.edu/carboncalculator)
Jones, Christopher M., and Daniel M. Kammen. “Spatial distribution of US household carbon footprints reveals suburbanization undermines GHG benefits of urban population density.” Environmental Science & Technology (2014).