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How to create advanced emissions inventories to set your city up for success

Manon Morel Fri, 14 May 2021
parameters climateos

Most city governments and their climate officers will recognise just how time-consuming and tiresome calculating  emissions inventories are for their area-wide emissions - especially when it is for international reporting obligations. The challenge is one of juggling many spreadsheets, research, calculations and the inevitable, and seemingly unresolvable gaps that they entail. Never more so than when local data is hard to come by.


And it’s no surprise, because creating a thorough emissions inventory is laborious and the guidance that exists out there is mostly made up of rigorous approaches that often exceed the local data and skills available. Even when completed, the inventory is never really over, as new emissions inventories need to be compiled in the years that follow to assess the progress towards targets.


Those city governments lucky enough to be provided with a basic top-down emissions inventory from their national government may have an easier time from a reporting perspective, but it will not necessarily make for a better inventory, that is, an inventory that can be harnessed for concrete action by utilising transparent parameters related to local activity. 


All in all, creating a good emissions inventory is a step that can’t be overlooked, as it forms the very basis of a city’s strategy and climate action plan and is also a crucial part of the reporting process. But what if we envisioned inventories differently? 


In this article, we’ll discuss how we can make the inventory process smoother, more efficient and sophisticated, to provide a solid foundation for action. 


Why are emissions inventories a big deal? 


Emissions inventories account for greenhouse gases discharged in the atmosphere and document the sources of these emissions, usually sector-by-sector, for activities taking place within specific geographical boundaries. 


Creating a precise and comprehensive emissions inventory is a big deal because it’s the basis of a city’s climate action plan. If the foundation is flawed, the plan will be flawed, which means that the city’s externalities on the environment and climate change will go unchecked, so the inventory has to be as precise, and as evidence-based as possible. 


So, what’s the current framework for cities’ emissions inventories? 


The IPCC offers guidelines for national source-based accounting, but it does not apply to cities because of their smaller scale. In recent years, organizations have attempted to offer more guidelines and frameworks for cities’ GHG accounting processes. 


Together with C40, ICLEI  and WRI, the Greenhouse Gas Protocol has put together the Global Protocol for Community-Scale Greenhouse Gas Emissions Inventories (GPC) to act as a ‘global standard enabling comparison, benchmarking, and aggregation’. 


Yet, as stated by C40 itself, ‘the GPC is a reporting standard, not a methodology document’, which means that there is a lot of room for variation in the way an emissions inventory is created based on those guidelines. 


While it shies away from offering a concrete methodology, the GPC does provide some guidelines on how to create an inventory. It states that a city must estimate GHG emissions by multiplying activity data (e.g. kilometers driven) by an emissions factor associated with the activity (e.g. g CO2eq / kWh), which will depend on the technology and the type of fuel used. 


The bottom-line of a sophisticated inventory is bottom-up 


We couldn’t agree more with this ‘activity-first’ approach as this promotes bottom-up calculations which ‘provide detailed data on GHG emissions by transport mode, vehicle type, trip purpose, and fuel type, which are useful for designing intervention measures” as opposed to top-down approaches that are more vague and may “determine only the total GHG emissions from the sector.’ 


Top-down approaches are great for getting the big picture of a city’s emissions, and giving you a feel for the priorities and trends across sectors, but they are limited. They don’t help to pinpoint what exactly within a given sector is causing emissions and therefore, what to change in order to reduce them. 


One of the reasons why top-down is used so extensively, is that cities rarely have the data available or the expertise for bottom-up calculations. An example might be the difference between evaluating for the quantity of fuel sold which is an easier number to get a hold of, instead of the number of vehicle kilometers driven, which provides much more insights on the basis of activities that drive the demand for the fuel.


As such, the insistence of the GPC on providing a flexible framework and methodology stems from realistic concerns, and betrays a severe lack of data within cities, giving them the room they need to maneuver.


But even all that freedom offered by the framework is not enough and has not proven helpful for cities’ emissions inventories. In a study about the elaboration of GHG inventories based on the GPC, out of the 40 articles analysed as part of a systematic review, only one article reported it was entirely based on the GPC while all other authors were unable to ‘complete all the requirements of the GPC due to the enormous absence of activity data and low quality.’


It’s of real concern that there is still no globally viable approach for emissions inventories and GHG accounting.


At a time where cities are asked to be more accountable and to act on the climate challenge, it’s of real concern that there is still no globally viable approach for emissions inventories and GHG accounting. 


Many city planning departments are beginning to understand the value of bottom-up and grassroot approaches and actively seek to engage their citizens in co-creating the places they inhabit and the policies that affect them.


Likewise the value of bottom-up inventories in climate action planning is becoming paramount. Data that comes from the bottom-up is inherently better and more precise to make decisions at the local level. While this bottom-up data may be hard to come by, we can’t just discard it because it is what we need to set precise targets and get an accurate depiction of our city’s activities and associated emissions. Instead, we need to overcome the apparent data scarcity and work with what we do know, share the data we have, organise and use it more methodically, and spend more time on developing and executing plans. 


No data? No problem. 


The world’s most comprehensive platform to create Living Climate Action Plans, ClimateOS, comes pre-filled with data, making these activity-based, bottom-up calculations possible and automatic. The data is also fully customisable to incorporate the data climate strategists have worked to, and want to collect. 


The Activity Mapping Toolkit within ClimateOS enables a city to account exactly for the activities happening in a city and to calculate their associated Carbon Causal Chains (CCCs), resulting in a truly bottom-up city inventory that provides a baseline picture of what a city’s main carbon emitting activities are, and why. To make sure that these activities really do reflect what happens in a city, the data comprises more than 250 parameters, logically laid out according to our calculation model, which can be closely edited to reflect the nature of operations, cohorts, energy intensity and subsequent emission factors. 


All parameters come from scientific reports, national or other official statistics and also include our assumptions and data proxies for the data that, despite all our research, could not be found or verified. These powerful proxies are based on the normalised value and average parameters for a city’s size and population, population growth rate and average living area per capita, and solve the major hurdle of data scarcity which usually prevents cities from elaborating precise and actionable, bottom-up emissions inventories. It is more than this, it is helping people move on from simply focussing on inventories as an end in themselves.




While it encourages cities to account for emissions as broadly as possible, ClimateOS’s methodology is less tied to reporting scopes and geographical boundaries than other methodologies. It is instead based on Transition Targets, a set of universal, modular blocks that model shifts from high to low carbon states, which a city can choose to take responsibility for by selecting or removing Transition Targets. It is intended to be the starting point of being able to control and operationalise a plan to shift carbon emissions in the activities of the city no matter where they occur or what sector they belong to. As such, the solution proposed by ClimateOS is not that of a perfect emissions inventory, because there is no such thing. Or if there is, it is something we have little time for. Instead, it is a rigorous, evidence-based and responsibility-based approach, geared towards rapid action and iteration. 

Where to from here? 


Emissions inventories are undeniably tricky but the key to creating a comprehensive action-oriented inventory can be found in adopting the right approach, and the right tools, whilst simultaneously understanding what it is that the inventory should tell us other than what emissions were created last year in a narrow scope. 


For an inventory to be truly useful, it must be relatable and broken down in terms of its causal basis - that is what does it stem from -  down to the language and units of everyday delivery and policy.  You can only do this consistently and effectively by working bottom-up. 


This is the only way you can begin to control the nature of your transition, and more accurately model potential emissions reductions by understanding how activities and their operations might change. That’s why we need to start with an approach that focuses on creating a City Inventory from parameters to describe the work being done, the resources used, and from this, the emissions inventory is calculated, allowing you to continue to work on finding the path for your transition as you develop your Living Climate Action Plan.