An integrated approach to improving fossil fuel emissions scenarios with urban ecosystem studies

The future trajectory of fossil fuel emissions is one of the largest uncertainties in predicting climate change. While global emissions scenarios are ultimately of interest for climate modeling, many of the factors that influence energy and fuel consumption operate on a local rather than global level. However, there have been relatively few comprehensive studies of the ecological and socioeconomic processes that will determine the future trajectory of net carbon dioxide (CO2) emissions at local and regional scales. We conducted an interdisciplinary, whole ecosystem study of the role of climate, urban expansion, urban form, transportation, and the urban forest in influencing net CO2 emissions in the Salt Lake Valley, Utah, a rapidly urbanizing region in the western U.S. Our approach involved a detailed emissions inventory validated with atmospheric measurements, as well as a system dynamics model of future CO2 emissions developed in collaboration with local stakeholders. The model highlighted the importance of a positive feedback between urban land development and transportation investments that may strongly affect emissions by amplifying declines in developmental densities and increases in vehicular traffic. Simulations suggested that while doubling the density of tree planting would have a negligible effect on total urban CO2 emissions, land use and transportation policies that dampen the intensity of the urban sprawl feedback could result in a 22% reduction in CO2 emissions by 2030 relative to a business as usual scenario. We suggest that by advancing our mechanistic understanding of energy and fuel consumption regionally, this urban ecosystem approach has great potential for improving emissions scenario studies if replicated in other cities and urbanizing regions.