Our cities have the potential to be a key climate change solution. Already they are hot-beds of innovation in local and global approaches to the nexus of sustainability and quality of life. People who live in cities drive less, use less energy to heat, cool, and light their homes, and even their water and sewer lines are shorter and require fewer resources. (See related, “ The City Solution .”)
But all of those advantages – and the ability to save more land for nature and agriculture – will be cancelled out if our cities are ringed with suburbs that are profligate in their use of energy and resources. In my laboratory – the Renewable and Appropriate Energy Laboratory (RAEL) — at UC Berkeley's Energy and Resources Group, we decided to take a closer look at whether cities in the United States really are helping to shrink the nation’s carbon footprint. (See related Quiz: What You Don’t Know About Cities and Energy .)
Our results, just published in Environmental Safety & Technology , should give urbanization advocates kudos for what well-designed urban cores can do. But it also should give them pause, to not forget the suburbs. Population-dense cities indeed are contributing fewer greenhouse gas emissions per person than other areas of the country, but these cities’ extensive suburbs essentially “take back” the climate benefits of their cores. We are not talking just about commuting, either.
U.S. suburbs, in fact, account for half of all U.S. household greenhouse gas emissions, even though they house less than half the population. Taking into account the impact of all urban and suburban residents, large metropolitan areas have a slightly higher average carbon footprint than smaller metro areas.
The bottom line: Cities are not islands. They exist in a complex landscape that we need to understand better, both theoretically and empirically.
We wanted to present in a visually striking way the impacts and interactions of our energy, transportation, land use, shopping, and other choices in both cities and suburbs. It is plain to see the trends at our interactive carbon footprint maps for more than 31,000 U.S. zip codes in all 50 states at: http://coolclimate.berkeley.edu/maps .
“Metropolitan areas look like carbon footprint hurricanes, with dark green, low-carbon urban cores surrounded by red, high-carbon suburbs,” says Christopher Jones, the doctoral student who worked with me on the project. “Unfortunately, while the most populous metropolitan areas tend to have the lowest carbon footprint centers, they also tend to have the most extensive high carbon footprint suburbs.”
In fact, the average carbon footprint of households living in the center of large, population-dense urban cities ...
Read more on the National Geographic blog " The Great Energy Challenge ."
See related science article, " Suburban sprawl cancels carbon-footprint savings of dense urban cores ," on the UC Berkeley NewsCenter.