An integrated approach for estimating greenhouse gas emissions from 100 U.S. metropolitan areas

Cities have become key players in climate change mitigation policy. To develop their climate policies, cities need good assessments of their current and future emissions. We use publically available national datasets to develop an integrated approach for estimating GHG emissions at the metropolitan level over time, between multiple locations, and across sectors. We estimate consistent production-based GHG emissions for the 100 most populated metropolitan areas in the United States in 2014. We find that total 2014 metropolitan CO₂ emissions range from 4.1 million metric tons in Lancaster, Pennsylvania to nearly 170 million metric tons in the Houston, Texas; with an overall average of 27 million metric tons. The top 20 absolute emitters and top 20 per capita emitters only overlap for 9 locations. Per capita emissions also show a wide variation: from 5 metric tons per person in the Tucson, Arizona to 65 metric tons per person in the Baton Rouge, Louisiana; with an overall average of 14 metric tons per person. We also compute estimates for 2002 and 2011 and compare to our 2014 emission estimates. Across all locations analyzed, average total emissions increased by 3% and average per capita emissions decreased by 14%. Where possible, we also compare our emission estimates to those reported by the cities in their climate action plans and find an average absolute difference between our estimates and those reported by the cities of 5.6 metric tons CO₂ per person, likely due to temporal and scope differences between the two estimates. Our integrated emission estimation approach complements bottom-up approaches typically employed by municipalities and helps practitioners divert their attention and resources away from continuous emission accounting toward more impactful emission mitigation efforts. (letter)