Thomas Crawford, Saint Louis University, Saint Louis, MO, USA
Presentation Title: Urban form as a technological driver of carbon dioxide emissions: A structural human ecology analysis of on-road and residential sectors in the conterminous U.S.
This research integrated themes from GIScience, land change science and structural human ecology to investigate the influences of urban form on U.S. CO2 emissions in the on-road and residential sectors. The STIRPAT human structural ecology paradigm was extended by theorizing urban form as a sociotechnical system to be included as a technological driver within frameworks seeking to understand CO2 emissions. County-level 2002 emissions data are assembled from the Project Vulcan dataset. A remote sensing classification product is used to quantify spatial composition measures of urban form for 3,108 conterminous U.S. counties. Spatial error regression models were estimated that alternately insert variables measuring population and developed area. This strategy enabled new interpretations of the effects of population, affluence and urban form. Implications are that a focus on urban form provides policymakers greater leverage for carbon mitigation compared to the structural human ecology's traditional focus on population and affluence. However, the effects of urban form must be tempered by recognition of their modest quantitative magnitude compared to the much larger effects made possible by transition to cleaner energy sources and less consumptive human behaviors.
Key Lessons Learned
- Results confirm prior findings for the effects of population and density and original results suggesting urban heat island effects for residential emissions and carbon reduction benefits achievable through a developed land-use mix containing a greater proportion of high intensity relative to low-intensity land-use.
- Urban form matters, but it matters differently in terms of sign, significance and interpretation depending on emission sector and metro versus non-metro status.
- Models show demonstrable reductions in emissions associated with greater density and greater share of land-use in the higher intensity class.
Policy/Practice Implications of Research
- Assuming that income effects are positive in all cases, positive population and income effects provide limited avenues for mitigation strategies. However, policymakers in U.S. counties and municipalities therein desire strategies that promote economic growth.
- Growth entails an increase in population due to new jobs and associated multiplier effects. While increased income is certainly desirable, it has the undesirable effect of increasing emissions.
- Focusing on the most basic STIRPAT variables of population and affluence seem to limit options to either a no growth or slow growth agenda; shifting focus to strategies beyond these most basic variables offers more a more expanded set of strategies.
- Behavioral modification and clean technology development are two strategies with greater potential, but also difficulties related to challenges in behavior modification and the longer time horizons associated with transition to cleaner energy sources.
- Stronger consideration of developed land-use patterns has the potential to give actors in this socio-technical system greater leverage to enact mitigation strategies. However, the effects of urban form must be tempered by recognition of their modest quantitative magnitude compared to the much larger effects made possible by transition to cleaner energy sources and less consumptive human behaviors.
Knowledge Gaps and Needs
- More work involving mixed methodologies to investigate urban form as a technological driver of CO2 emissions is needed.
- There is a need to assess the degree to which practices and knowledge of actors in the urban and regional planning profession reflect connections between urban form and emissions. Interviews and surveys of these professionals can elucidate these connections.
- Content analysis of local, state and regional policy documents (i.e., climate action plans) is needed to assess the degree to which urban form as a mitigation strategy enters the policy arena.
- There is spatial variation in the strength of urban form as a driver of emissions. Quantitative modeling using spatial techniques, such as geographically weighted regression, are needed to understand this variation.
- The role of urban form and urban heat island effects must be studied in more depth, i.e., heat island effects are typically viewed as a bad thing to be mitigated, however, heat islands may have the opposite effect in winter by increasing temperatures and thus contributing to less fossil fuel consumption for home heating.
- What are the net effects of heat islands on CO2 emissions? How do net effects vary geographically by climate type?
- Improvements in spatially explicit emissions data are needed and better evaluation of uncertainty is paramount.
- Temporally explicit data are also needed at fine spatial scales (counties or gridded products), in order to more formally model change as opposed to cross-sectional analysis for a single year.