City-Scale GHG Accounting Methods: Implementation, Approximations, and Policy Relevance

Greenhouse Gas (GHG) emission inventories for cities and city regions are confounded by the small spatial scale of cities and by trans-boundary infrastructures, travel, and trade-of-goods and services between cities. This study will compare three GHG emission methods in 45 U.S. counties side-by-side, to evaluate:

• Implementability – How does data availability facilitate method implementation in each county.
• Policy Relevance – How can the GHG inventory findings be used for policy relevant decisions.
• Inter-City Comparability – What are the best available metrics for comparing GHG emissions across cities.

The three different methods are:

• Traditional geographic based methods measure GHG emissions occurring from end-uses of electricity and fossil fuels from buildings and surface transport, community-wide, and are similar to production based inventories.

• A geographic-plus (or hybrid) GHG inventory, builds upon WRI GHG protocols. The method includes most policy-relevant trans-boundary activities such as commuter & airline travel, and life-cycle based embodied energy of key materials such as transport-fuels, water, shelter, and food, used in all cities. Both the geographic and geographic-plus methods, consider the entire community together, including all residential-commercial-industrial activities.

• In contrast, consumption-based GHG inventories, measure GHG emissions resulting from economic final-demand, dominated by household consumption, all trans-boundary GHG’s, including international imports. Unlike geographic-plus, here the community is divided, with commercial-industrial activities for exports not counted in local boundary.

The side-by-side comparison will help address the practical value-added of all three methods in helping cities measure and reduce GHG emissions.