Carbon solutions across the transect

Average Annual Total Footprint

New work from UC Berkeley shows the difference in household carbon intensity across the US by zip code, and probably affirms what many suspect – the suburbs are responsible for more carbon pollution on a per household basis then their core cities.  Households in the center of large urban areas were found to emit 50% below the national average, while their suburban counterparts were found to emit 50% more.  The study produced some great maps you can use to explore your region.

A couple of things are unique/interesting about this study over other core/burbs environmental footprinting efforts, however.  This one used econometric data and accounted for consumption of goods and services, not just the typical bubble-over-the-city approach which only looks at things coming out of tailpipes and chimney stacks.  Household income and expenditure surveys were used to estimate greenhouse gas footprints from goods and services, a key piece that is missing from many inventories.

By looking at economics as well, this study captured more nuance about urban form and emissions:

Increasing population density alone, for example, appears not to be a very effective strategy for reducing emissions. A 10-fold increase in population density in central cities corresponds to only 25 percent lower greenhouse gas emissions, and “high carbon suburbanization results as an unintended side effect,” Jones said.

Increasing population density in suburbs is even more problematic, he said. Surprisingly, population dense suburbs have significantly higher carbon footprints than less dense suburbs, due largely to higher incomes and resulting consumption.

What’s up in the Twin Cities?  There’s definitely a range in emissions with the expected pattern, but most of the difference is due to transportation and housing size, not so much the difference in goods and services consumed.  And if you look at the map of just household energy carbon footprint, you can see emissions from the home are dominated by electricity, since we’re in the coal-heavy Midwest.  Many western states have very low electricity emissions, but have higher transportation emissions.

Household Energy Carbon Footprint

Carbon solutions should be tailored to their location, the study notes.  In the suburbs, there’s a lot more space for solar, and that solar could be used to electrify the transportation system.  A separate Australian study found that urban locations up to 12 dwelling units per acre would much produce more than their daytime consumption (keep in mind Australia is a sunny place), with the excessive being used for the transportation system.

solartransect copy

From Measuring the Solar Potential of a City and its Implications for Energy Policy, H. Byrd, A. Ho, B. Sharp, N. Nair

The UC Berkeley study is producing estimates, not actual measurements, but they are fairly robust.  They use local emissions coefficients for electric grids, for example.  Transportation and income data come from the Census and other sources.  The fact that they’ve added consumption data to help broaden the conversation beyond our buildings and cars alone makes this a significant contribution.  Plus the cool maps.

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4 Responses to Carbon solutions across the transect

  1. David Levinson
    David Levinson January 9, 2014 at 6:28 am #

    Also note that household sizes (number of persons) varies by location. Cities have smaller households (and thus less consumption) than suburbs on average.

  2. Alex Cecchini
    Alex Cecchini January 9, 2014 at 8:47 am #

    I agree that consumption is an important part of the CO2 equation, but it seems odd to link it with a land-use/transportation discussion. For example, saying that densifying suburbs is problematic because of the higher incomes, and therefore consumption, seems to miss that those with higher income will likely consume more no matter where they live. I’d be interested to see consumption data across fixed-incomes (and household size) varying by home/lot size and location. My guess is that people with more space in their homes, larger yards, etc consume more than their more compact peers.

    David makes a good point that HH size matters in consumption, but for reference, the average household in Minneapolis is 2.22 (avg family size 3.11), and in Lakeville those numbers are 2.99 and 3.32.

    However, as a gut check, the households in Minneapolis zip code 55409 consume (guesstimate by eyeballing the charts) 19-20 mtCO2, and has an average HH size of 2.4 and family size of 3.27, while Lakeville households consume 26-27 mtCO2. This is a ~35% increase in consumption for an average household that is 25% larger. It’s only one data point (and I always use Lakeville since it’s where I grew up), but does show a mismatch.

    • Alex Cecchini
      Alex Cecchini January 9, 2014 at 9:17 am #

      Ah, the site itself has a calculator that gives averages for output: http://coolclimate.berkeley.edu/carboncalculator

      If you fix income (for example, I picked $80-99k/year) and household size (3 people), consumption (food, goods, services) in 55044 is 33.1 mtCO2 and 27.24 in 55409, a 21.5% increase.

      Also, meant to say it the first time – great write-up and pragmatic takeaways. I think the context-sensitive solutions by region and even zip code is a major takeaway for reducing average household footprints. I think for the Midwest it’s pretty obvious that we’ll see huge reductions by 1) a changeover in electricity production to cleaner sources, and 2) electrification of the vehicle fleet (in that order).

  3. Ed Kohler January 9, 2014 at 9:30 am #

    Minneapolis actually does pretty well for solar potential (not quite Australia levels, but better than people generally expect). For example, the estimate I recently had done for my .095 acre property predicts that I can generate 98% of my electricity consumption on-site, and still have room for some solar thermal panels to cover my hot water needs. Granted, my house happens to have a south facing roof, which makes it easier to capture that energy than a E-W roof does.

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