City and County of Honolulu Greenhouse Gas Inventory

The City and County of Honolulu (City) Inventory of Greenhouse Gas Emissions (GHG Inventory) is part of the City’s commitment to mitigate GHG emissions and develop a comprehensive climate action plan (CAP). This initial GHG Inventory for the City was developed by the Office of Climate Change, Sustainability and Resiliency (Resilience Office) and measures annual direct and indirect GHG emissions, represented in metric tons of carbon dioxide equivalent (MTCO2e) for the years 2005, 2015, and 2016. The primary sources of GHG emissions in the City are stationary fuel and electrical energy use in residential, commercial, and industrial buildings; energy used to refine oil and gas products for the electricity and transportation sectors; on-highway, off-highway, marine, and air transportation that occurs within the City limits or transits between Oʻahu and domestic destinations; water and wastewater treatment and solid waste management; industrial processes and product use (IPPU); and agriculture, forestry, and other land use (AFOLU).

The GHG Inventory is the first step toward creating an island-wide CAP. The findings will be used as a starting point to determine emissions reduction targets over time; to identify and prioritize economy-wide and sector-specific carbon mitigation strategies for achieving reduction targets; and to gauge progress towards those goals.

The City GHG Inventory is developed under the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC Protocol) and estimates GHG emissions that occur in the City’s jurisdiction encompassing the entire island of Oʻahu. The GPC Protocol is a generally-accepted carbon emissions accounting and reporting standard for cities and municipalities developed by the World Resources Institute, C40 Cities Climate Leadership Group, and ICLEI – Local Governments for Sustainability. The year 2005 acts as a baseline to measure progress against the United States’ nationally determined contribution (NDC) to global GHG emissions as agreed under the Paris climate agreement. City staff chose 2015 to coincide with the State of Hawaiʻi’s latest GHG Inventory, and then updated to 2016 using the most up-to-date data, as of March 2019.

The Resilience Office consulted with ICLEI staff and AECOM, its Resilience Strategy development partner, to apply best practices under the GCP protocol, identify quality data sources, and employ credible estimation and scaling methods. The Resilience Office utilized two publicly available GHG inventory tools – ClearPath and CURB – to organize and segment the inventories, and to apply standard emissions factors by fuel-type, i.e., MTCO2e per unit of fuel/energy type consumed. Resilience Office staff also coordinated decisions regarding data sources and methods with staff at the County of Hawaiʻi, County of Kauaʻi, and County of Maui; and collaborated with other stakeholders as part of the review committee for the State of Hawaiʻi’s GHG Inventory developed by the Clean Air Branch of the Department of Health. The Resilience Office cross-referenced its sources and methods with the State’s 1990, 2007, and 2015 GHG Inventories released in December 2008 and February 2019, and for some sectors with limited data availability, used the State inventory as a starting point from which to extrapolate and scale.

The City’s community-wide inventory is designed to be updated and improved on a periodic basis as new techniques and data become available.