Published 13 Aug 2022
Updated 18 Aug 2022
J Poore and T Nemecek's 2019 paper, published by the University of Oxford, suggests that today's food supply chain contributes 26% of total anthropogenic GHG emissions [1, p. 1]. Further, meat, aquaculture, eggs and dairy use ~83% of farmland and account for ~57% of Greenhouse Gas emissions , despite providing only 37% of our protein and 18% of our calories [1, p. 4]. They conclude that a transition towards plant-based diets could result in a land-use reduction of 76% and a 49% reduction in GHG emissions. Herein, GHG emissions, carbon emissions and food emissions all refer to GHG emissions.
Mike Berners-Lee builds on this (and other) data to provide new perspectives on the impacts of consumer dietary change [2, 3]. Their data aggregation highlights how conscious everyday choices can influence individual carbon footprints. For example, a Meat & Dairy-based weekly shop (UK) accounts for around 61kg of carbon, whereas a Vegan-based weekly shop accounts for around 36kg of carbon emissions, a 40% reduction. This data, combined with Public Health England data on daily calorie meal proportions underpins the approach for this food emissions tool.
Table 1 shows the average carbon impact of Vegan, Vegetarian, and Meat & Dairy diets which has been extrapolated from the 'week's food shoppping' data in 'How Bad are Bananas?' [2]. Additional data for 'No red meat' diets and consideration for food waste and food miles are included in [2, p. 113-114], but are omitted here to reduce user decision fatigue and complexity.
| Diet | Weekly Carbon Impact (kgCO2e) | Annual Carbon Impact (kgCO2e) | Daily Carbon Impact (kgCO2e) |
|---|---|---|---|
| Vegan, average | 36 | 1872 | 5.13 |
| Vegetarian, average | 46 | 2392 | 6.55 |
| Meat & Dairy, average | 61 | 3172 | 8.69 |
Table 2 shows estimated daily proportion of food and drink intake per meal according to Public Health England [4].
| Meal | Proportion of Daily Intake |
|---|---|
| Breakfast | 20% |
| Lunch | 30% |
| Evening Meal | 30% |
| Everything Else (e.g. food and drink snacks) | 20% |
Rather than requiring people to provide an itemised breakdown of all foods and drink consumed and their resultant carbon impact (e.g. [5, 6]); a simpler approach is taken. Here, people need only provide information about which diet was followed for each meal on each day. This reduces the time and resources required to submit this data, improving the chances of representative data submission.
To calculate carbon emissions for each meal, the calculation used is:
Meal Carbon Emissions (kgCO2e) = Proportion of meal daily intake
* Diet emissions per day (kgCO2e)
To calculate the carbon emissions for each day, the sum of all Meal Carbon Emissions is taken. This is possible because the tool restricts user input to allow only one breakfast, lunch, evening meal and 'everything else' per day, resulting in 100% proportional meal (and therefore carbon emission) representation.
This methodology takes only one aggregated, averaged food emissions data source into account, and could be improved to include a range of data to better reflect scientific consensus. Future methodology versions could introduce a wider array of data sources.
This methodology assumes a daily breakfast, lunch, evening meal and 'everything else' (snacks) meal structure. Those not following this structure are requested to document their meals 'representatively', to reflect their diet throughout the day (via error message). While this may introduce some data inconsistency, the impact is expected to be minimal.
Further, this methodology assumes individual carbon emissions for time periods of 1 day or more. This is not suitable for one-off meals (e.g. business lunches) or for more than one person. These scenarios should be accounted for manually; or multiple forms should be submitted.
Since this tool relies on individuals to record their consumption, time or resource use constraints may limit data collection, resulting in data inconsistencies being introduced. Organisations may mitigate for this effect by encouraging data submission.
[2] 'How bad are bananas?', Mike Berners-Lee, Profile Books, 2020
[3] 'There Is No Planet B', Mike Berners-Lee, Cambridge University Press, 2021