{"id":2227,"date":"2010-07-28T17:38:50","date_gmt":"2010-07-28T23:38:50","guid":{"rendered":"http:\/\/www.boulderblueline.org\/?p=2227"},"modified":"2010-07-29T19:05:51","modified_gmt":"2010-07-30T01:05:51","slug":"does-dense-make-sense-part-3-density-and-carbon-footprint","status":"publish","type":"post","link":"http:\/\/www.boulderblueline.org\/?p=2227","title":{"rendered":"Does Dense Make Sense? Part 3. Density and Carbon Footprint"},"content":{"rendered":"

Editor’s note:\u00a0 PLAN-Boulder County<\/a> has issued a report entitled <\/em>Does Dense Make Sense? <\/strong> This is the third part in a six part series extracted from the report.<\/em><\/p>\n

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Urban farming -- photo courtesy Tim Plass<\/p><\/div>\n

As the world strives to reduce greenhouse gas (GHG) emissions, we face a conundrum:\u00a0 whereas we all have to reduce our individual carbon footprints, the climate is sensitive to the total<\/em> GHG content of the atmosphere.\u00a0 As cities like Boulder work to make progress toward Kyoto goals (8% below 1990 emission levels by 2012) and beyond, we need to reduce total carbon footprint regardless of changes in population.\u00a0 Fortunately, Boulder\u2019s population has been growing at a rate slightly below 1% and we have a willing and dedicated citizenry that has indicated its support for climate action by passing the Climate Action Tax and the ClimateSmart loan program.\u00a0 Nonetheless, our population has grown by approximately 20,000 since 1990, or about 28%, which adds to the intensity of per capita reductions that are required.\u00a0 Additional population growth, even at our relatively slow current rate, which could double our population in 70 years, will make it that much more difficult to achieve Kyoto goals and goals defined by the Governor\u2019s Energy Office (20% reduction from 2005 levels by 2020 and 80% by 2050).\u00a0 Fortunately, the City of Boulder is projected to reach \u201cbuildout\u201d in 2035 with a population of 119,400, but other Boulder County communities need to seriously consider the GHG consequences of growth.<\/p>\n

In this section, we examine the impact of the built environment on carbon footprints (GHG emissions).\u00a0 Much has been written in recent years about potential advantages of dense housing in reducing per capita GHG emissions due to close, convenient availability of mass transit, insulating effects of common walls in multiunit housing, and the heat island effect that warms ambient air around dense developments (Haughey, 2005; Ewing, et al. 2008).\u00a0 Lower per capita GHG\u2019s in densely populated areas were illuminated when local and regional monitoring of atmospheric emissions as part of air quality studies were subjected to GIS analysis<\/a>.\u00a0 These studies<\/a> (Gurney et al., 2009) show, predictably, that major cities put out very high net greenhouse gases and pollutants (Figure 1), but a surprising outcome of these studies is that per capita emissions are noticeably lower than in rural areas (Figure 2).\u00a0 Estimates of total per capita GHG reductions vary widely, however, ranging from 20-40% (Ewing et al.) to 70% (http:\/\/www.cnt.org\/<\/a>).\u00a0 This extreme range suggests that methodology is still evolving, that estimation of carbon footprint for an area is a complex endeavor, and that careful examination of individual factors that affect GHG\u2019s is warranted.<\/p>\n

Figure 1.\u00a0 Total CO2<\/sub> emissions in the U.S.<\/h2>\n

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Source:\u00a0 http:\/\/www.purdue.edu\/eas\/carbon\/vulcan\/index.php<\/address>\n

Figure 2. Per capita CO2<\/sub> emissions in the U.S.<\/h2>\n

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Source:\u00a0 http:\/\/www.purdue.edu\/eas\/carbon\/vulcan\/index.php<\/address>\n

Transportation<\/h1>\n

We have already seen that denser housing concentrated around transit centers offers advantages in reducing vehicle miles traveled and especially single occupant vehicle usage.\u00a0 Both the Transportation Research Board (2009) report and Ewing et al. indicate that dense housing development offers a savings in vehicle miles traveled of 7-12%. \u00a0This translates directly to a similar reduction in GHG\u2019s due to transportation advantages.\u00a0 Greater savings may ensue if additional transit-friendly programs such as managed parking and convenient bus-train-bike-pedestrian facilities are offered.<\/p>\n

Energy and Land Use Patterns<\/h1>\n

Attached housing offers some advantages in reducing GHG\u2019s related to home heating and electricity usage.\u00a0 Ewing and Rong used data from the U.S. Residential Energy Consumption Survey, house types from the Census Bureau\u2019s Public Use Microdata Sample, and house size statistics from the Census Bureau to conclude that nationwide housing in compact development results in less energy use and GHG emissions by 20-40% relative to detached housing. This is due to:<\/p>\n