The implications of scope and boundary choice on the establishment and success of metropolitan greenhouse gas reduction targets in the United States

In recent years, cities across the United States have devoted considerable attention and resources to developing greenhouse gas (GHG) inventories and climate action plans (CAPs). Using integrated metropolitan-level GHG estimates from publicly available national datasets, we explore the implications of inventory scope and boundary choices for 41 metropolitan areas across the United States. We quantify emissions from 'under-reported' activities (i.e. emissions from industrial processes and from transportation between urban and suburban areas) and 'under-reported' geographies (i.e. emissions from all activities occurring within the metropolitan area, but outside the city limits), and find that, in most cases, these 'under-reported' emissions constitute a considerable portion of total metropolitan emissions. Given the important role local CAPs continue to play in national-level GHG reduction efforts, there appears to be much to gain from continuing to expand the scope and boundaries of local-level GHG accounting and reduction actions. This analysis helps illustrate why transitions toward policies at the regional (as opposed to the city level) may be warranted, as well as highlights some key issues that may arise as local-level GHG policies continue to evolve and expand. For example, if local decision-makers choose to expand the scope and/or scale of their policies, GHG reduction plans may warrant substantial alterations to baseline emission levels, targeted annual emission reduction rates, overall emission target levels, or the number of years needed to achieve a desired emission reduction. Ultimately, the manner in which these policies evolve will determine their overall contribution to national and international climate mitigation efforts.