Calculating your GPC community inventory - Part 4 - 100% Renewables

Calculating your GPC community inventory – Part 4



In our first blog post in this series, we introduced community emission inventories. In the previous articles, we examined categories and scopes of the Global Protocol for Community-scale Greenhouse Gas Emission Inventories (GPC) and looked at the differences between a BASIC, BASIC+ and a territorial inventory. In this article, we discuss how you can calculate your community’s emissions.


Calculating versus measuring carbon emissions

It is possible to measure carbon emissions. Examples are monitoring greenhouse gas emissions from a coal-fired power plant or measuring the emissions from exhaust pipes in vehicles. In most cases, however, you will calculate emissions by applying a so-called ‘emissions factor’.

How are greenhouse gas emissions expressed?

Greenhouse gas emissions are expressed in tonnes of CO2-e (carbon dioxide equivalent).

When reporting under the GPC, you need to record greenhouse gas emissions of every gas, plus the tonnes of CO2-e.

Free Whitepaper – Calculating Your GPC Community Inventory

What is CO2-e?

Every greenhouse gas has a different global warming potential (GWP) over 100 years. The GWPs are determined by the Intergovernmental Panel on Climate Change (IPCC). The most current assessment of GWPs was released in 2013 in IPCC’s Fifth Assessment Report (AR5).

When reporting your community inventory, you should use the latest IPCC Assessment Report or the version used by your country’s national inventory body.

Australia, as an example, uses the Fourth Assessment Report (AR4) when converting different greenhouse gases to CO2-e. Carbon dioxide is assigned a GWP of 1. Methane has a GWP of 25 and nitrous oxide has a GWP of 298. These GWPs are used to convert greenhouse gases into one single measure, CO2-e.

As an example, if 1,000 tonnes of methane emissions are emitted in your community, this would translate to 25,000 tonnes of CO2-e.

Activity data and emission factors

Calculations are based on converting data that you have available into emissions using a ‘conversion’ or an ‘emissions factor’.

GHG emissions = Activity data x emissions factor

Activity data measures a level of activity that leads to greenhouse gas emissions. Examples of activity data are:

  • Electricity consumption
  • Natural gas consumption
  • Litres of fuel used in a car
  • Tonnes of waste sent to landfill
  • Number of sheep

An emissions factor converts your activity data into a mass of greenhouse gas emissions.

Example of calculating emissions associated with electricity consumption

Say your city consumed 1,000 MWh of electricity. The emissions associated with your electricity use differ depending on how this electricity is generated. If mostly fossil fuels like coal are used to produce electricity, then this will produce more emissions compared to renewables.

Let’s take a look at the emissions resulting from the same electricity consumption in three different English-speaking countries by applying the relevant emission factors.

Figure 1: GHG emissions of different countries with the same underlying electricity consumption

The emissions for Australia are higher than for the USA and the UK with the same underlying consumption due to most of the electricity being produced from fossil fuel sources.

Note on emission factors:

The factors for Australia and the USA are averages across all regions for 2019.

Factor sources:

Selecting an appropriate calculation methodology

Selecting a calculation methodology depends on several things:

  • The purpose of your GHG inventory. Considerations here include whether you are reporting internally or to your community, or whether you are participating in programs like the C40, or the Global Covenant of Mayors.
  • Availability of data. Some data may be easily obtainable, whereas, with others, you may need more comprehensive data gathering methods.
  • Consistency with your country’s national inventory reporting programs. You may need to select a specific calculation methodology to fit in with how your country reports its national inventory.

No matter what calculation method you choose, you need to make sure to document the calculation method you have used.

Data collection

A big (and the most time consuming) part in calculating a community’s inventory is data collection.

If you are lucky, you have existing data for your selected inventory boundary and the reporting level you have selected. If not, you will have to generate new data (which involves surveying your community) or adapt existing data.

Examples of data sources

The following shows a list of possible data sources you could use (as described in the GPC):

  • Government departments
  • Statistics agencies
  • Your country’s national GHG inventory report
  • Universities and research institutes
  • Scientific and technical articles in environmental books, journals and reports
  • Sector experts/stakeholder organisations

Identifying emission factors

Your first choice of emission factors should be local, regional, or national factors published by the Government. If these are not available, you can use IPCC default factors or data from the Emission Factor Database, or other standard values from international bodies that reflect national circumstances. Table 2.2 of the 2006 IPCC Guidelines provides a comprehensive guide to identifying potential sources of emission factors.

Free Whitepaper – Calculating Your GPC Community Inventory

Quality assessment of activity data and emissions factors

Ideally, you would want the most accurate activity data and emissions factors you can get. However, this will not always be possible, and sometimes, you need to trade-off between accuracy and completeness of your inventory. Generally speaking, you would prefer your data and emissions factors to be:

  • Reliable
  • Peer-reviewed
  • Reputable
  • Robust
  • Recent
  • Specific to your area
  • Publicly available

To be compliant with the GPC, you need to evaluate both the quality of your activity data as well as that of your emission factors. The quality can be low, medium or high as shown in the graphic below.

Figure 2: Assessing the quality of activity data and emissions factors

How to calculate the most common emissions in a GPC inventory

The following section provides more guidance on how you can calculate the most common emission sources in your GPC inventory.

Calculating emissions from stationary energy consumption

Examples of stationary energy consumption are electricity and natural gas use.

Step 1 – Gather activity data

Obtain activity data for each fuel type, ideally disaggregated by sub-sector (e.g. residential buildings, commercial buildings, etc.). Ideally, you would get this data from the network provider or utility. If this is not possible, you can survey your community, or model the energy consumption by determining energy intensities by facility type.

If you cannot disaggregate the data into sub-sectors, you can apportion the total consumption information to each sub-sector or building type. If data is not available for your city, you can use regional or national consumption data scaled down to your population size.

Step 2 – Calculate emissions:

Multiply the fuel/electricity consumption with an appropriate emissions factor.

Calculating emissions from transportation

Emissions from transportation can be difficult to calculate. Transportation consists of the sub-sectors on-road, railways, water transport, aviation and off-road transportation. In this article, we are focusing on on-road transport. Please refer to the GPC for guidance in calculating other transportation-related emissions.

When it comes to on-road transportation, there is a large variation in available data, and the GPC does not prescribe a specific method. Most cities start with a top-down method that uses fuel consumption as a proxy for travel behaviour. It’s fairly easy to calculate emissions this way and does not require a high level of technical capacity, but it makes it difficult to track emission reduction actions.

With more accurate or relevant information available over time, cities tend to change their method to a more detailed, bottom-up approach. Bottom-up methods use detailed activity data, such as vehicle km travelled per mode and vehicle fuel intensity.

Step 1 – Choose calculation method:

The GPC encourages cities to calculate emissions based on four common methods and recommends the induced activity approach.

  1. Fuel sales method (top-down)
  2. Induced activity method (bottom-up) – transportation emissions induced by the city, including trips that begin, end, or are fully contained within the city (usually excluding pass-through trips).
  3. Geographic or territorial method (bottom-up) – emissions from transportation activity within city boundaries
  4. Resident activity method (bottom-up) – emissions from transportation activity undertaken by city residents

Step 2 – Gather activity data:

If you have chosen the fuel sales method, you can obtain data from fuel dispensing facilities or tax receipts. Where this is not possible, data may be available at a regional scale, which can be downscaled based on vehicle ownership data.

If you have chosen a bottom-up method, you need to obtain data from models or surveys.

Step 3 – Calculate emissions:

Multiply the fuel/electricity (electric vehicles) consumption with an appropriate emissions factor.

Calculating emissions from waste

Here, you calculate waste that is not being recycled, and ends up in landfill, biological treatment or incineration. Biological treatment refers to composting and anaerobic digestion of organic waste.

Step 1 – Choose calculation method:

Choose the calculation method

  1. First order of decay (FOD) – emissions are calculated based on actual emissions during the calculation year
  2. Methane commitment (MC) – emissions are calculated based on waste disposed in the calculation year

Step 2 – Gather activity data:

Obtain activity data from waste collection services and weigh-ins at the landfill site. Alternatively, you can multiply the per capita waste generation rate by the population. If you have chosen the FOD method, you will also need to collect historical waste data.

Step 3 – Calculate emissions:

Depending on the method chosen, calculate emissions based on guidance given in the GPC.

Calculating emissions from wastewater

Step 1 – Gather activity data:

Obtain the quantity of wastewater generated in your community, how it is treated (aerobically – in presence of oxygen, or anaerobically – in absence of oxygen), the wastewater’s source and its organic content.

Step 2 – Calculate emissions:

Calculate emissions for methane and nitrous oxide based on guidance given in the GPC.


It is challenging to develop carbon footprints that are in alignment with the GPC. Sometimes, it is easier to get the help of an expert who can guide you through the process. Here at 100% Renewables, we are certified City Climate Planners, proving our experience in community-level GHG emissions inventory accounting.

If you need help with developing community emissions inventories or pathways for emission reduction, please contact  Barbara or Patrick.

Feel free to use an excerpt of this blog on your own site, newsletter, blog, etc. Just send us a copy or link and include the following text at the end of the excerpt: “This content is reprinted from 100% Renewables Pty Ltd’s blog.

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