By Michael Doust, Programme Director, Measurement and Planning

The IPCC’s “Global Warming of 1.5°C” report calls for rapid, far-reaching and unprecedented changes in all aspects of society, including our cities, in order to mitigate the impact of global climate change and build a safer, more sustainable world for us all. Given the short-time frame and scale of change that is needed, evidence-based decision-making is now more important than ever to ensure that actions taken will deliver on the goals of the Paris Agreement. Underpinning this is the need for access to high quality, timely and interactive data on greenhouse gas (GHG) emissions. 

It has been four years since C40, in collaboration with ICLEI and the World Resources Institute, launched the Global Protocol for Community-Scale Greenhouse Gas Emission Inventories (GPC)1  at COP20. The GPC was developed to help cities estimate their city-wide GHG emissions in a consistent and transparent manner using a robust framework, following internationally-recognised GHG accounting principles. This allows for more credible reporting, public availability and more meaningful analysis of climate data.

To celebrate this milestone and demonstrate the value of taking a data-driven approach to tackling climate change, we have produced a series of infographics, based on analysis of over 160 GHG emission inventories from 60 C40 cities that have adopted the GPC. These graphics help to illustrate the benefits of having a consistent and comprehensive global standard and give insight into the drivers of urban GHG emissions.

The adoption of the GPC by C40 cities has many benefits, including: 

Regular reporting of GHG emissions supports monitoring of performance over time. Cities like Boston with multiple historical GHG emission inventories can demonstrate clear progress in reducing GHG emissions.2 This kind of data also allows cities to better understand why GHG emissions are changing, in turn allowing for better decision-making in setting targets, developing policy and communicating with stakeholders.

Aggregation and comparison of GHG emission inventories enables key emitting sectors to be identified, regional patterns to be observed and similarities and differences between cities to be explored. For example, across C40 cities, an average of 63% of GHG emissions come from building energy use, 28% from transportation and 9% from the treatment and disposal of waste. Looking at the data city-by-city, however, emissions associated with waste can make up anything from 5% to 40% of total city-wide emissions.

The GPC requires cities to disclose the underlying activity data and emission factors used to estimate GHG emissions. This data helps explain what is driving GHG emissions. The infographic below, for example, shows how building energy efficiency and electricity grid carbon intensity have an impact on building-related GHG emissions across different cities.

Cities are also asked to assess the quality of both the activity data and emission factors used to estimate GHG emissions. This information helps identify where future improvements could be made. Across C40 cities, data for the buildings sector is deemed to be more reliable than both the transportation and waste sectors, whilst activity data, in general, is found to be more reliable than the emission factors used to convert this into GHG emissions.

Effective climate action must begin with developing a GHG emission inventory. In less than four years, the GPC has become the most popular GHG emission inventory standard used by cities reporting to the CDP Cities platform. By encouraging cities to adopt a common reporting framework, the GPC helps build accountability and trust, whilst simultaneously delivering an insightful breakdown and comparison of city GHG emissions upon which successful, evidence-based climate action planning can be built.


1 WRI, C40, and ICLEI (2014) Global Protocol for Community-Scale Greenhouse Gas Emission Inventories. Web published at:

2 See also Doust, M. (2018) Peaking Emissions: An important milestone on the road to Paris. Web published at:

3 Activity data is a quantitative measure of a level of activity that results in GHG emissions taking place during a given period of time (e.g., volume of gas used, kilometers driven, tonnes of waste sent to landfill, etc.). An emission factor is a measure of the mass of GHG emissions relative to a unit of activity. For example, estimating CO2 emissions from the use of electricity involves multiplying activity data on kilowatt-hours (kWh) of electricity used by the emission factor (kgCO2/kWh) for electricity, which will depend on the technology and type of fuel used to generate the electricity. 

4 CDP (2018) 2017 – Cities Community Wide Emissions. Web published at:

Share article

More Articles