The Global Protocol for Community-Scale Greenhouse Gas Inventories (GPC) provides a standardised framework for cities to measure and report greenhouse gas (GHG) emissions. The GPC adopts two complementary approaches: accounting for emissions from production and consumption activities within city boundaries and categorizing emissions as scope 1 (territorial), scope 2 (grid-related), or scope 3 (transboundary).  

The GPC outlines methodologies for compiling city-wide GHG inventories. Part II emphasizes sourcing activity data and calculating emissions by applying emission factors to activity levels, such as electricity usage or kilometres traveled. While specific methods are not mandated, alignment with IPCC guidelines and national inventories is recommended. GHG emissions are reported in metric tons and converted to CO2 equivalents (CO2e), ensuring transparency and comparability. 

To use the GPC, cities must define inventory boundaries that encompass geographic areas, emission sources, and timeframes. Emissions are classified across six main sectors: stationary energy, transportation, waste, industrial processes, agriculture, and external emissions linked to city activities. The protocol provides methodologies for calculating and reporting these emissions while addressing potential double-counting issues. It also supports cities in setting mitigation goals, tracking performance, and improving inventory quality. 

Designed to enable aggregation at subnational and national levels, the GPC aids in improving national inventory data, assessing the impact of city-level mitigation actions, and exploring innovative strategies for GHG reduction across boundaries. This comprehensive framework ensures that cities can play a pivotal role in global climate action while maintaining transparency and methodological rigor.  

Key methods

Cities’ GHG emissions primarily originate from key sectors, each with distinct pathways and challenges in emissions quantification: 

– Stationary Energy: The largest GHG contributor, emissions stem from fuel combustion in residential, commercial, and industrial buildings, as well as power generation. This sector also includes fugitive emissions during fossil fuel extraction and transportation. 

– Transportation: Covering all modes, including road, rail, and air travel, this sector’s emissions arise from fuel combustion and grid-supplied electricity use. The GPC offers flexibility for cities to account for transportation emissions, considering variations in data availability and modeling methods. 

– Waste Management: GHGs are released during aerobic and anaerobic decomposition, incineration, and biological treatment. Methane recovery and energy-related incineration emissions are redirected to stationary energy accounting. 

– Industrial Processes and Product Use (IPPU): Emissions result from chemical or physical material transformations, such as in steel production or ammonia manufacturing. Additionally, consumer products like refrigerants can emit GHGs during usage and disposal. 

– Agriculture, Forestry, and Other Land Use (AFOLU): This sector produces emissions from livestock, land-use changes, and agricultural practices, while also offering the potential for GHG removals through sustainable practices. 

These evidence-backed sectoral insights emphasize the importance of tailored, comprehensive methodologies for accurate GHG accounting at the city level, fostering actionable climate strategies. 

Demonstration results

Emission calculation methodologies define the calculation formulas and necessary activity data and emission factors to determine total emissions from specified activities. Cities should select the most appropriate methodologies based on the purpose of their inventory, availability of data, and consistency with their country’s national inventory and/or other measurement and reporting programs in which they participate. An overview of methodologies outlined in the GPC is provided in Appendix C in the report.  

In IPCC Guidelines, three hierarchical tiers are used to categorize the methodological complexity of emissions factors and activity data. Tier 1 uses default data and simple equations, while Tiers 2 and 3 are each more demanding in terms of complexity and data requirements. Tier 2 methodologies typically use country-specific emission factors. These tiers, if properly implemented, successively reduce uncertainty and increase accuracy. The GPC does not use tiers to define methodologies but makes references to them when referring to IPCC Guidelines. 

The core of GHG emissions calculation lies in estimating emissions by multiplying activity data with corresponding emission factors. Activity data quantifies the level of activity producing emissions, such as energy consumed (in kilowatt-hours), kilometers traveled, or waste sent to landfills. Emission factors provide the rate of GHG emissions per unit of activity, e.g., kilograms of CO2 emitted per kilowatt-hour of electricity, varying with the energy source and technology. 

Data collection is critical and can originate from sources like government departments, national GHG inventory reports, academic institutions, and sectoral experts. Priority is given to local and national data, but adjustments may be needed when the geographical or temporal scope of available data doesn’t align with the inventory boundary. Scaling factors are employed to harmonize such discrepancies.