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Thoughts about the relationships between transport and the urban area it serves

“Beefing Up Population Density Won’t Curb Greenhouse Gas Emissions”

with 4 comments

I have put the headline in quotation marks as it does not reflect  my opinion – nor does it seem to be based on a very reliable way of forecasting policy outcomes. The headline comes from Atlantic Cities but the research itself is published in Environmental Science and Technology. The title there is “Spatial Distribution of U.S. Household Carbon Footprints Reveals Suburbanization Undermines Greenhouse Gas Benefits of Urban Population Density” (citation shown at foot of this article). And of course you and I do not have the right credentials to actually read this on line unless you are willing to pay a very hefty fee. But at least Berkeley provides a longer item than Atlantic Cities does and this is where their quotes are lifted from

As you will note, other readers have already taken exception to the conclusions that are quoted by Atlantic Cities, so I am not alone at being troubled by the attention getting headline. Because it does not seem to be adequately supported. I also am troubled since I have been advocating and teaching the exact opposite for many years now. First as part of the Community Energy Planning activities of the BC Energy Aware Committee – now the Community Energy Association – and latterly as part of a program for  people wanting to become Sustainable Building Advisors under the the LEED program, sponsored by the Canada Green Building Council. The thrust of my message has been – and still is – the putting up the greenest building possible is not going to achieve emission reductions if you put it in the wrong place and everyone has to drive to get there. Sure the building itself may perform flawlessly but the trips the building’s activities generate will more than make up for the energy savings achieved over more conventional technologies.

Denser urban areas do indeed perform far better – in terms of energy consumption and hence reduce greenhouse gas emissions – than less dense ones, and that is exactly what the maps that accompany the article show.

carbon denver

This just happens to be Denver – and you can also see the smaller city of Colorado Springs off to the left (west) which shows the same doughnut ring pattern of carbon emissions. And they do observe “large metropolitan areas have a slightly higher average carbon footprint than smaller metro areas.” But that may just be that in the US (and the data they use only comes from there) the larger metro areas have proportionately more suburbs.

People who live in denser urban areas do not need to make as many trips by single occupant motor vehicles as those who live in less dense areas. People who work in city locations are much less likely to have drive during their work hours than those in suburban office parks. If you can get what you need within a short walk then you are less likely to need to drive. In places like downtown Vancouver, the vehicle most likely to be used for most trips is the electric elevator. Moreover building technologies and simple physics favour denser areas notably when the designers are thinking holistically. Community energy systems are more efficient than individual systems. The village on False Creek, for instance, gets some of the heat for its buildings from the sewers. Many buildings in city centres need more cooling than heating, so careful siting and interconnectedness produces a better overall outcome than locating them at greater distances where this is not efficient in economic or energy terms.

But there are also all sorts of other benefits from greater densities. Indeed density in and of itself may not be the answer. Better density – the right kind of density – is almost always going to have better results no matter what metric you use. We happen to be concerned in this case with reducing greenhouse gas emissions but exactly the same responses work if you are looking to create a happier human environment, or one that preserves land for food production or recreation, or reducing traffic congestion, or cutting public expenditures. The arguments made by Charles Marohn for Strong Towns are almost entirely financial.

Actually I think what is really at play here is Atlantic Cities looking for a headline rather than better understanding. What the researchers are actually saying is that there is no one size fits all solution and that increasing density does not of itself produce the best outcomes. But it is also clear that continuing with business as usual, widening freeways and building new ones, refusing to invest in transit, sticking with strategies that favour “drive until you qualify” suburbs and so on is a recipe for disaster. And increasing density is often going to be a significant part of the solution.


Christopher Jones *† and Daniel M. Kammen *†‡§
†Energy and Resources Group, ‡Goldman School of Public Policy, and §Department of Nuclear Engineering, University of California, Berkeley, California 94720, United States
Environ. Sci. Technol., Article ASAP
DOI: 10.1021/es4034364
Publication Date (Web): December 13, 2013
Copyright © 2013 American Chemical Society
*Phone: (510) 643-5048. E-mail:, *Address: Renewable and Appropriate Energy Laboratory, University of California, Berkeley, CA 94720-3050. Phone: (510) 642-1640. Fax: (510) 642-1085. E-mail:

4 Responses

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  1. The real lesson from our two paper series:

    Jones, C. M. and Kammen, D. M. (2014) “Spatial distribution of U.S. household carbon footprints reveals suburbanization offsets benefits of population density”, Environmental Science and Technology.

    and the earlier paper:

    Jones, C. M. and Kammen, D. M. (2011) “Quantifying lower-carbon lifestyle opportunities for U.S. households and communities”, Environmental Science and Technology, 45, 4088–4095.

    is that there is not a ‘one size fits all’ response, and that best practices are emerging all over. Portland has done wonderful things on urban mass transit (and has an exceedingly low car ownership rate per household as a result), while bike corridors and bike availability in Washington DC have made real impact there, while congestion pricing in London and ‘fee-bates’ should be looked at in a number of cities, etc … are all operational parts of an emerging solutions space for a more holistic view of household energy, transportation, food, and goods and services.

    As an example, our online national data (at the zip code level)

    and our calculator tools that can be used by households, cities, schools, and businesses:


    allow one to see how different a given home/school/business appear.

    This permits an understanding of the opportunities for metropolitan areas to think through how to design low-carbon systems that also provide a superior quality of life.


    Daniel Kammen

    January 7, 2014 at 12:08 pm

  2. A couple additional responses to FAQ:

    Do the data suggest there are no benefits to increasing population density?

    Answering this question would require time series data; tracking how the carbon footprints of city residents change over time as population density increases. This is an important research question that deserves additional study. The current study compares the carbon footprint of households in population dense locations with those in less dense locations for a single year.

    The study results do suggest the following:
    1. Population dense suburbs have significantly higher carbon footprints than less dense suburbs, primarily due to higher incomes.
    2. Population dense central cities have significantly lower carbon footprints than less dense central cites; however, these cities also have more extensive suburbs. When considering the net effect of all metropolitan residents (suburbs and central city residents together), larger, more populous and population dense metropolitan areas have slightly higher average carbon footprints than less populous and lower population dense metropolitan areas. 
    3. There is no correlation between population density and household carbon footprints when considering all zip codes, all cities, or all counties. Low carbon footprint and high carbon footprint locations are found at all levels of population or population density, with the exception of very high population dense city centers, which are consistently low. 

    Does the data reflect local policies, like energy codes?

    While the paper uses locally-specific data, 37 variables in total, it does not include the effect of many location-specific policies, like energy codes. Cities with stronger energy codes will be lower than our estimates. Transportation policies are reflected somewhat better since we have good data on vehicle ownership, commute times, public transit usage, commute modes, etc.

    Chris Jones

    January 7, 2014 at 1:20 pm

  3. The title seems counterintuitive to other publications and seems to assume the post war suburban model will be with us forever.

    My Christmas break reading included two very interesting books. Both “A Country of Cities” by Vishaan Chakrabarti and “Walking Home” by Ken Greenberg supply data that not only place emissions at the upper part of the scales for suburbs, but provide information that defines the limitations of suburbanization. Fossil energy costs and public and private financial instability are the two largest. The rejection of the suburbs and the adoption of urbanity by younger generations is also a measureable factor.

    The suburbs may indeed cancel much of the emissions savings of the city, but it appears the suburbs will not be sustainable for much longer, and the natural trend is toward urbanization.

    The differences between these two books are that Chakrabarti advocates for “hyperdensity” as the primary solution to peak oil and climate change, and feels this idea is exportable. He is an architect with SHoP Architecture in NYC and he backs what he says with environmental and economic performance stats on a number of projects he was involved with, and compares performance stats between cities. Now before one concludes that he is pushing the cheek to jowl massive tower blocks of Hong Kong, he strongly advocates nothing less than mixed use zoning and access to light and air for each building. He is also one of the most vocal advocates of high capacity public transit and a singular transit orientation for all development I have ever read.

    Greenberg is a bit more gentle in his assessment of cities which is based on decades of experience from all over the world, but based in Toronto. His conclusions about urban sustainability are similar to Chakrabarti’s but he is more focussed on the street and neighbourhood than on individual buildings. Greenberg is trained in architecture but advocates a multidisciplinary and highly consultative and consensus building urban design process as the most legitimate approach to finding solutions and defining option. He lists many professions that need to learn to work together to rebuild our cities, and is highly disdainful of any individual professional who claims to have The Answer and of any formulaic, prescribed method promoted on heterogenuous communities. He is a strong advocate of the public realm, and of course of mixed use and fully recognizes the great utility of public transit. He spent a decade with a public sector Urban Design Division with the city of Toronto which was responsible for much of the successful redevelopments in that city’s fine inner core neighbourhoods, and he was sad to note that they were too late to save some fine heritage neighbourhoods and buildings that were destroyed by Autotopia. Would that Vancouver and any of its Metro sister cities had an Urban Design Division with many disciplines.

    Greenberg also knew and was a personal friend of Jane Jacobs both in Manhattan and Toronto. He praised her continually in his book for her intuitive insights and advocacy for neighbourhoods. He draws to our attention how she eas never formally trained in planning or architecture and rejected many honourary doctorates throughout her life. She found formulaic ideas about urban design repugnant and always referred to the damaging formulaic planning policies that destroyed huge swathes of our cities with freeways. Cities are evolutionary constructs with millions of transactions with money and energy ocurring every day and paint-by-numbers formulae are just too inadequate. Greenberg was appalled to see Jane Jacobs’ name co-opted in hundreds of anti-development protests when in fact Jacobs approved of density and went about attaching economic performance criteria to density (e.g. “import replacement” in big cities as theorized in several of her books). Thete she was, photographed by the Vancouver Sun on the Concord Pacific seawall praising that development not just for its density, but for using point towers as a device to save 40% of the land as open green space and for giving the waterfront over to public ownership.

    City building and city fixing are about so much more than just lowering emissions. I was ver fortunate to have had the opportunity to read these books back to back. The contrast between them was as educational as the content.


    January 9, 2014 at 4:59 pm

  4. Having not read the above posts and comments and links all the way through yet I am not sure if the authors separated out the emissions from coal fired themal power plants from buildings and vehicles. Portland’s coal plant has been used as a cudgel against its significant progress in relatively sustainable urbanism, basically lumped in with all emissons and therein inflating the totals. It does seem ironic, though, that a progressive city relies on one of the dirtiest fuels around. However, there may be some cross-jurisdictional forces at work (city vs.state for example).


    January 9, 2014 at 5:59 pm

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