Get the app
Understanding and managing one's carbon footprint is crucial in the fight against climate change. Through consumption, individuals influence 65% of global emissions. By making collective and conscious spending choices, demand for a more sustainable and inclusive economy can be driven. Tweak, an award winning South African sustainability platform, has developed a robust methodology to calculate carbon footprint scores based on daily activities and transactions. This paper details the methodology employed by Tweak, highlighting its unique features and relevance to South African users.
Individual's daily activities, from the food they eat to the purchases they make, have carbon emissions embedded in them. Transactional data provides a detailed and quantifiable record of an individual's spending habits, directly reflecting their consumption patterns. By analysing this data, it is possible to estimate the carbon emissions associated with various activities, such as purchasing goods, using transportation, and consuming household utilities.
At Tweak, transactions are tracked and categorized by type, including Household, Food, Goods, and Transport. While the carbon footprint of food-related services is calculated, services that are outside the user's control, such as education or healthcare, are excluded (click here for more information). These categories are then used to calculate a carbon footprint score, reflecting an individual's impact on the environment.
For each transaction, we multiply the amount you spent in that category by its respective carbon emissions multiplier either following a top down approach (spend-based methodology) or a bottom up approach (product-level methodology) depending on the level of information available.
Tweak's spend-based methodology estimates carbon emissions by dividing the total emissions produced by the industry by the total monetary value of all transactions within that industry. For instance, if the clothing industry emits 500,000 kg of CO2 and generates 1,000,000 rand in sales, the average emissions rate is 0.5 kg CO2 per rand spent. It relies on the Exiobase dataset(1) , a widely used emissions database.
To estimate the carbon footprint of a purchase, Tweak multiplies the transaction amount by this emissions rate. For example, spending R500 at Mr Price, with an emissions rate of 0.5 kg CO2 per rand, results in an estimated carbon footprint of 250 kg CO2. This approach is particularly useful when detailed product-level data is unavailable.
For transactions where detailed product-level data is available, Tweak uses a product-based methodology. This approach utilises product footprint databases, such as Our World In Data (2), which provide average emissions data for specific products based on Life Cycle Analysis (LCA). LCA considers the entire lifecycle of a product, from production to disposal, providing precise emissions estimates.
For example, if a user spends R500 at an Engen petrol station, Tweak calculates the carbon footprint by using the average emissions data for petrol provided by the database. The process involves dividing the transaction amount by the price per liter of petrol and then multiplying it by the average CO2e emissions per liter of petrol.
Tweak enhances the accuracy of carbon footprint calculations by using quiz information to incorporate qualitative data. The quiz covers aspects like diet, household size, commuting habits, and energy usage, which allows Tweak to tailor estimates to individual lifestyles and behaviors.
For instance, grocery purchases are adjusted based on dietary preferences. A vegetarian diet results in a lower carbon footprint compared to a meat-based diet. If no specific electricity transactions are found, Tweak uses the quiz data to estimate the electricity footprint, ensuring all significant sources of carbon emissions are accounted for.
If someone lives in a household with four people, Tweak divides the carbon footprint of shared expenses, such as groceries and utilities, by the number of household members. This approach provides a more precise estimate of each person's carbon footprint.
Moreover, Tweak adjusts the CO2 footprint of purchases from sustainable and local retailers. This encourages individuals to make more environmentally friendly shopping choices and supports sustainable and local businesses, promoting a more sustainable and inclusive economy.
Tweak initially assigns categories to transactions based on merchant and transaction details. For greater accuracy, users can manually recategorise transactions if they are misclassified. For example, a purchase at an Engen petrol station might be categorised as Fuel, but if it was actually for food, users can correct it. This manual adjustment ensures more precise carbon footprint calculations.
Each transaction category is assigned a confidence score to reflect the accuracy of the estimate. Categories relying on spend-based data receive lower confidence scores due to their generalised estimates, while categories with product-level data receive higher confidence scores due to their precision.
Tweak regularly validates its carbon footprint estimates by comparing minimum, maximum, and average CO2 footprints against local averages. This process ensures alignment with the South African average CO2 footprint. Tweak continuously updates carbon emissions multipliers and product-level data based on recent studies, government reports, and user feedback to maintain accuracy and relevance.
In summary, our carbon accounting software calculates an individual's carbon footprint score by combining top-down and bottom-up approaches with qualitative information from the quiz. We continually strive to improve the accuracy of our estimates by using the most up-to-date data available and refining our methods.
(1) https://www.exiobase.eu/index.php/about-exiobase
(2) https://ourworldindata.org/co2-emissions
