As the effects of climate change become ever more apparent, the accurate measurement of GHG emissions is becoming increasingly important to better understand their sources and how to best reduce them.
GHG emissions are released into the atmosphere through economic activities or processes that emit hydrocarbons. To measure these, a carbon dioxide equivalent (CO2e) value is given relative to the activity associated with the release of the GHG; this is known as an emissions factor (EF).
EFs are how activity data is converted into GHG emissions. The number of activities that necessitate EFs to measure their GHG emissions is huge, these activities include things like fuel combustion, waste landfilling, electricity consumption, vehicle travel, purchased heat and steam, animal agriculture, etc.
To add to the complexity of EFs, each activity or process not only produces a different kind (or a mix) of GHGs (CO2, CH4, N20, HFCs, PFCs, Sulfur Hexafluoride, and Nitrogen TriFluoride), each of which traps heat in the atmosphere at different rates and has a different atmospheric lifetime. But each EF also varies in the locale they are emitted.
Global warming potentials
All hydrocarbons are not created equally. Different GHGs can have different effects on the Earth’s warming, the Global Warming Potential (GWP) allows us to compare the global warming impacts of different GHGs. The heat-trapping ability of each gas measured against CO2’s over a 100-year period (GWP) provides a common unit of measure for stakeholders to compare emissions reduction opportunities across gasses.
The second most common GHG, methane (CH4) for example has a global warming impact 56 times that of CO2 in a 20-year period and has a relatively short atmospheric lifespan of 12.4 years. The impact of GHGs potential for trapping heat and atmospheric lifetime can vary greatly. Sulfur hexafluoride can reach as much as 23,500 times the CO2 warming potential, and stay in the atmosphere for 3,200 years.
The GWP of methane for instance is 25, therefore if 1 tonne of methane is emitted it is equivalent to 25 tonnes of CO2, or 25 tonnes of CO2e.
GWP could be considered analogous to currency exchange rates where instead of converting all currencies into one unit of monetary value (e.g., USD), they convert all GHGs into one unit of global warming - CO2-equivalents (CO2e)
Emissions per unit of output
The direct measurement of GHG from a physical source is rare, which is why emissions factors are needed to measure the CO2e emissions of an activity.
Generally, emissions factors are averages of current and available data and need to be updated regularly, as long-term values can change in different localizations, leading to uncertainty in the data.
For example, the Emission factor of bituminous coal changes depending on where it is emitted, it is 25.75 kilojoules/kiloton CO2e in Nigeria, whereas in Australia it is 24.39 kilojoule/kiloton CO2e.
These are just two examples of the over 18,000 emissions factors in the IPCC database, and countless other thousands that exist in other databases. All of which convert activity data ranging from bituminous coal like the example above to animal agriculture like Dairy cows, (1,175kgCO2e/head/year) and everything in between.
When it is not possible to collect activity data, spend-based data is then used to approximate emissions. Spend-based data takes the cost of a purchase and multiples it by an emissions factor to provide an estimate of emissions per dollar spent. This method is much less accurate than activity data as it takes a rough approximation of an industry average across the relevant country. However, because of challenges in collecting activity data for companies, especially across the value chain (Scope 3), spend-based data is currently the most common way of estimating emissions.
Difficulties in measurements
Within emissions factors there is always a parameter of uncertainty in the accuracy of the activity data estimate, usually expressed as a percentage range (+/- 5%). This is because activity data is based on a generic dataset of averages, which may not be close to the reality of the emissions. The level of uncertainty can vary greatly between countries, some of which may not have rigourous methods of data collection.
Uncertainty must be taken into account when measuring emissions, as it can affect the credibility of emissions calculations. With emissions factors there are four types of uncertainties:
- Parameter uncertainty: a measure of how close the emissions factor is relative to the actual emissions. For example, for the global warming potential of methane the uncertainty range is -30% and +40%.
- Model uncertainty: the limitations of a model to replicate the actual reality of an activity.
- Situational uncertainty: Include assumptions of how a product will be used and disposed of.
- Methodological uncertainty: Includes the assumption of the correct unit of measurement used, such as miles traveled over fuel consumed.
There is a lot of complexity in calculating the emissions of one activity, however, that complexity is compounded when considering the number of activities an organisation has in its operations. For this reason, a software solution is needed, Persefoni’s software platform has been able to codify 107,000 emissions factors, thus far allowing their users to make simple GHG calculations. With software, organisations can automate data uploads and calculations of all of their business activity and spend data in real-time.
Measuring emissions is not an easy practice, all of the above need to be considered when creating an emissions inventory for an organisation. Emissions factors allow for emissions to be measured when there is a lack of data, or if data is messy and includes different GHGs and business activities. Allowing organisations to measure the full scope of their carbon emissions is the first and most important step to start reducing them.
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