The urbanization and growth of the human population over past decades has yielded cities of unprecedented size and form, which emit significant quantities of waste, transform habitat, modify major biogeochemical cycles, alter local climate, and diminish human health. Carbon exchange is a key indicator of the intensity and pattern of urban metabolism, but the state of science currently does not address the close coupling of carbon exchange within and across human and natural subsystems of urban and urbanizing systems. Almost all research has focused on urban carbon emissions, or separately on urban vegetation carbon exchange. Thus, it is not possible to answer basic questions such as whether natural systems exchange carbon more locally than they do with a metropolitan region. This research will develop an integrated measurement and analysis framework for coupled carbon exchange in an urban-to-rural gradient from Boston to the rural Harvard Forest Long Term Ecological Research Site. This project will combine ground-based measurements of carbon exchange and energy flows with socioeconomic, meteorological and satellite measurements and modeling of human activity and the built and natural environments. These data will be integrated into a dynamic, Geospatial Information System that will characterize extant patterns of carbon exchange from daily to seasonal time scales at sub-meter spatial resolution across the urban-to-rural gradient. This analytical framework will then be used to forecast carbon exchange impacts of future land use change and urban growth scenarios, to advance fundamental knowledge about coupling of carbon exchange in urbanizing systems, and provide policy makers with specific and relevant information to align urban growth planning with sustainability goals.
Quantifying climatic, ecological, and socioeconomic drivers of carbon exchange and energy use will allow for forecasting carbon flows and evaluating policies aimed at altering flows consistent with social goals. For example, this research will help evaluate options for achieving Boston's emissions reduction targets. More broadly, it provides tools for larger-scale efforts like the Massachusetts Global Warming Solutions Act, the Regional Greenhouse Gas Initiative, and the American Clean Energy and Security Act. Because this research includes natural and social science determinants at fine spatiotemporal resolution, it can evaluate options that cannot be assessed within a single discipline and anticipate unintended consequences for the human population. For example, this research can be used to evaluate how urban forestry, changes in rooftop albedo, and changes in transportation infrastructure can offset carbon emissions, or to examine how transportation options affect both carbon emissions and the economic opportunities available for urban dwellers.
We conducted a detailed examination of Boston’s "Urban Metabolism", using the element carbon as a currency in the urban economy, and as a platform to (a) advance fundamental understanding of coupled human-natural systems in cities; (b) produce policy-relevant outcomes to increase Boston’s environmental sustainability; and (c) serve as a research model for cities around the nation. Because cities are responsible for nearly three fourths of global carbon emissions, cities are "ground zero" for human-caused climate change, but also represent the largest opportunity for improvement. Through field and a network of tower-based measurements of carbon, in the forms of biomass, carbon dioxide, and methane, we identified where and when carbon is exchanged in Greater Boston at an unprecedented fine level of resolution. Our study results, published in several peer-reviewed journal articles, demonstrate (1) that the scale at which carbon emissions are measured is a crucial determinant of the estimated quantity of emissions; (2) that operational definitions of "urban" have large impacts on estimated urban carbon stocks and flows; and (3) that a potentially large amount of greenhouse gas emissions may be leaking through aging urban natural gas pipeline infrastructure. These research results underscore the need for a consistent urban measurement protocol and set of definitions (not only for Boston but for cities around the nation and world), and the efficacy of combined mobile and tower measurements of carbon exchange that can quantify both expected emissions sources (such as automobiles and buildings) and can uncover unexpected emissions sources such as methane-leaking pipeline infrastructure. Broader impacts associated with this research have included direct engagement with and education of a wide variety of urban stakeholders, including residents of diverse neighborhoods (Back Bay Neighborhood Association; Madison Park Community Development Corporation and Housing Project); City of Boston staff; and public school children in Boston, Cambridge, Brookline, MA, in coordination with a climate change-themed NSF GK-12 project. Our methane research has had the broader impact of informing state policy, through three separate legislative testimony appearances at the Massachusetts State House; and federal policy through legislation to repair leaking natural gas infrastructure proposed by Senator Edward Markey (D-MA).
