Mitigation of methane emissions in cities: How new measurements and partnerships can contribute to emissions reduction strategies

• Published in: Earth's future 2016-09, Vol.4 (9), p.408-425
• Main Authors: Hopkins, Francesca M., Ehleringer, James R., Bush, Susan E., Duren, Riley M., Miller, Charles E., Lai, Chun‐Ta, Hsu, Ying‐Kuang, Carranza, Valerie, Randerson, James T.
• Format: Article
• Language: English
• Subjects: Air pollution; Anthropogenic factors; biogenic; Cities; Climate change; Climate change mitigation; Cooperation; Emission measurements; Emissions; Emissions control; ENVIRONMENTAL SCIENCES; fossil; fugitive; Gas leaks; Greenhouse effect; greenhouse gas; Greenhouse gases; Methane; Methane emissions; mobile; Natural gas; Natural gas distribution; Organic wastes; Outdoor air quality; Partnerships; Pollutants; Population; Researchers; Target recognition; urban; Urban areas; Urbanization; Waste disposal
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1002/2016EF000381

Cities generate 70% of anthropogenic greenhouse gas emissions, a fraction that is growing with global urbanization. While cities play an important role in climate change mitigation, there has been little focus on reducing urban methane (CH4) emissions. Here, we develop a conceptual framework for CH4 mitigation in cities by describing emission processes, the role of measurements, and a need for new institutional partnerships. Urban CH4 emissions are likely to grow with expanding use of natural gas and organic waste disposal systems in growing population centers; however, we currently lack the ability to quantify this increase. We also lack systematic knowledge of the relative contribution of these distinct source sectors on emissions. We present new observations from four North American cities to demonstrate that CH4 emissions vary in magnitude and sector from city to city and hence require different mitigation strategies. Detections of fugitive emissions from these systems suggest that current mitigation approaches are absent or ineffective. These findings illustrate that tackling urban CH4 emissions will require research efforts to identify mitigation targets, develop and implement new mitigation strategies, and monitor atmospheric CH4 levels to ensure the success of mitigation efforts. This research will require a variety of techniques to achieve these objectives and should be deployed in cities globally. We suggest that metropolitan scale partnerships may effectively coordinate systematic measurements and actions focused on emission reduction goals. Key points Unintended (fugitive) methane emissions are ubiquitous in urban systems, and come from biogenic as well as natural gas sources Methane emission sources and their magnitudes vary greatly among cities Urban methane mitigation will require new observations with a suite of techniques, and new institutional partnerships Plain Language Summary 70% of greenhouse gases emitted by humans come from cities. This number is growing as more of the world's population moves to cities. Cities have been active in reducing emissions of CO2, the most important greenhouse gas, but not of methane, the second most important gas. In cities, methane is mainly thought to come from natural gas handling systems, and waste disposal facilities. Both of these methane sources are growing over time; however, we do not know exact amounts or how fast these emissions will grow. We also do not know how much different methane sources