Study: city dwellers produce as much CO2 as countryside people do (but urban form still matters)

A new study of two metro areas in Finland proclaims to “illustrate that the influence of urban density on carbon emissions is insignificant”.  This study was published in Environmental Research Letters.  You might remember other studies that seem to indicate the opposite.

The idea that urban form has a significant impact on emissions and therefore should be considered during planning and land use decisions is embraced by many urbanists, environmentalists and scholars.  Others disagree with this position, saying us “sanctimonious urbanites” may be overplaying our hand.  I don’t think this latest report really does anything to resolve the “GHG blame game” (or, as I prefer to call it, an accurate accounting of externalities).  In fact, if you look at the data, it supports the notion that land use and transportation decisions and patterns have a significant impact on emissions.  While trying to avoid sanctimony, let’s look at the details.

While traditional approaches to inventorying emissions look at sources associated with activities occurring inside a community (transportation, energy consumption etc), this study uses a life-cycle assessment model to calculate emissions.  This means that the responsibility for emissions associated with a product, service or transaction is assigned to the consumer, not to the producer.  In other words, if you buy a TV, the emissions associated with the resource extraction, manufacturing, transportation and operation of that TV are all assigned to you, not the factory that manufactured it.  Using traditional methods of emissions calculation, you (or your city) may only be assigned the emissions from some of the transportation of the TV to you, and the electricity it uses.

I haven’t really noticed that urbanists, scholars and others interested in assessing emissions impacts of urban form are claiming density or street networks or transit access  influence how many TVs people buy, how many plane trips they go on, or how many dragon fruits they eat.  This study seems to imply otherwise:

The prevailing belief is that dense metropolitan areas produce less carbon emissions on a per capita basis than less dense surrounding rural areas. Consequently, density targets have a major role in low-carbon urban developments.

When you include lifecycle assessment of goods, the study says, per capita emissions for “city” and “rural” residents are about the same.  Basically, the study results boils down to this: the city tends to house richer people and richer people will buy more goods and services, therefore they create more carbon emissions in a global sense.  Even if city dwellers emit less through transportation, those emissions are more than made up by their swank houses, lawn care service and jet-set lifestyle.  Gotcha smug urbanists!

Except.  There are a few problems with this study.  First, some methodology problems.

First, this study looks at two relatively small metro areas.  TheHelsinkimetro is under 1 million and theTamperemetro under 400,000.  Applying these results to the rest of the country (or the world) seems premature.

This study uses an economic input-output method of life-cycle assessment for calculating emissions from goods and services (the details of which I won’t go in to).   This in turn relies on national survey data of consumer behavior for data on expenditures on certain products.  This survey data is a national average for each income group¹.  For example, the survey says Finns with a household income of X spend, on average, Y on TV dinners each year.  The lifecycle assessment tool then tells you for every Y dollars you spend on TV dinners, the supply chain produces Z emissions.  The problem is, this average expenditure figure is capturing information from household income groups in various locations (city and rural) across the country with no way of distinguishing between the two.

This makes the consumption emissions portion (emissions not from transport or housing) of the study suspect.  The authors admit as much:

The rest of the carbon categories, the consumption of goods and services, reflect clearly the effect of income on the emissions. However, this part of the carbon consumption was not the focus of this study, and also cannot be analyzed in depth with the presented hybrid model. The model shows that traveling abroad and the use of services grow as earnings grow, as figure 1 shows, but regarding daily consumption, it is not possible to differentiate amount and quality.

While the authors note interestingly that building-related emissions are actually higher in more dense areas (lifecycle assessment includes expenditures on construction, repair, furnishing and equipment as well as electricity and heating energy use), they do say that private driving and public transportation “correlate rather nicely with urban density”.  This leads to my other problem with the study, which is that the authors seem to be confusing urban land use policy with global action on climate change.

The study’s introduction states,

From the urban development perspective, the current practice of assessing the emissions from some specific sub-sectors, such as buildings or transportation, does not seem sufficient. It could be argued that all GHG emissions related to living and to consumer behavior should be included as part of the design of urban metabolism.

I totally agree.  However, what “sanctimonious urbanists” are saying is that urban form has an impact on emissions from transportation, which is directly tied to land use.  They mostly aren’t saying that it impacts purchasing decisions and global supply chains.  When the authors dismiss “density targets” for urban development, they seem to be confusing strategies within one emissions sector with a comprehensive, global climate policy.

Looking at the study data, it is clear that denser places have lower emissions from transportation per capita.  The least dense area in the study (RCT, orRuralCitiessurroundingTampere) has emissions from transportation per capita that are 25% higher than those from the densest area (Helsinki).  Combined, the “countryside” cities have per capita transportation emissions that are 17% higher than the “urban” cities.

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(Sidenote: before any American readers/writers get too carried away about this study’s transferability, note that even in the least dense areas (RCT), the share of total trip generation on public transportation is around 15% (!)  That number gives Randal O’Toole and Wendell Cox night terrors.)

Lifecycle analysis for emissions is a relatively new field.  As we learn more about emissions from the supply chain, we should be ready to respond as a society and these emissions should be included in our planning for climate action.  What tools do local decision-makers have to address emissions from the global supply chain?  Not many.  Individual consumers can take some action (buy products with less packaging, buy fewer products, recycle or reuse as much as possible), but it’s nearly impossible for average consumer to understand the global CO2 emissions impact of any individual product.

Data from this study supports the idea that decisions about urban form can have a significant impact on climate change.


¹ This is how consumer expenditure surveys work in the US, and I assume the Finnish surveys are similar, although I can’t read Finnish.  I’m relatively confident they didn’t go to every town in Finland to collect this survey data, in fact it’s pretty unlikely since their sample size is only 10,000.

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