Studierendenwerk Bonn: CO₂ traffic lights in the canteens: Studierendenwerk Bonn

Making informed decisions: CO₂ traffic light system in the Studentenwerk Bonn canteens

The meal plans published by the Studierendenwerk Bonn specify a CO₂ equivalent (CO₂eq) value for each dish. This is based on the Eaternity-Datenbank and is calculated in collaboration with partners from the academic community. A traffic-light rating system classifies the dishes according to their carbon footprint: green indicates a comparatively low carbon footprint, whilst red indicates a comparatively high one compared with the other dishes on offer.

The CO₂ equivalent value has already been calculated and displayed for most dishes. The basis for these calculations is continuously updated and expanded. All information is provided without guarantee; errors, changes and misprints are reserved. No liability is accepted for the accuracy or completeness of the information.

Key to the CO₂ traffic light system

Depending on the level of CO₂ emissions in grams, traffic light colours are assigned using a three-point scale.

Green	At least 50 per cent lower CO₂ emissions than the average for the dishes being compared.
Yellow	Lower CO₂ emissions than the average for the dishes being compared.
Red	Higher CO₂ emissions than the average of the dishes being compared.

Important: We assess the dishes/side dishes/products regardless of portion size. The assessment takes nutritional values into account and is standardised to a standard portion (corresponding to a weight of approximately 500 g and approximately 560 kcal – depending on the nutritional values). This means that even if a portion is smaller, this does not automatically mean that the CO₂ emissions are lower. This allows whole dishes to be compared, including side dishes.

Why does the red light come on for the side dish ‘leaf salad’? Because of its comparatively low nutritional value (kcal).

You can view Eaternity’s 3-point rating system here.

Other factors

When calculating an extended environmental score, CO₂ emissions are taken into account as one of the key parameters in the food production system. Compared with the other indicators – water, animal welfare and rainforest – the reduction of greenhouse gas emissions has a particularly significant impact on a dish’s resource consumption. The Studierendenwerk has therefore initially opted for a CO₂ traffic light system to present the CO₂ emissions of dishes as clearly and transparently as possible. Dishes are supplemented with organic labels or information on animal welfare criteria where relevant, verified evidence is available.

Where does the data come from?

Methodology of the Eaternity database

The Eaternity database contains CO₂ equivalent values and unit processes for all common foods, based on seasonality, cultivation methods, transport, preservation and processing models. A greenhouse model has been developed here to determine the CO₂eq emissions associated with heating greenhouses in both organic and conventional agriculture. The individual CO₂eq values are the result of collaboration with researchers from the Zurich University of Applied Sciences (ZHAW) and the Quantis World Food Database, the University of Zurich (UZH), the Swiss Federal Institute of Technology Zurich (ETHZ), the Research Institute of Organic Agriculture (FiBL), ecoinvent v3.6, Agribalyse, Agrifootprint, peer-reviewed literature and other reports; supplemented by Eaternity’s own research, which has been adjusted to ensure better comparability.

Further information on the Eaternity CO₂ footprint:

Guidance: The ‘Planetary Health Diet’ as a scientific framework

A scientific framework for the further development of the diet is the so-called “Planetary Health Diet”. It stems from the report published in 2019 by the EAT-Lancet Commission, which involved 37 scientists from 16 countries – including climate researchers and nutritionists. The Commission’s aim was to establish a scientific basis for a more globally sustainable food system. The ‘Planetary Health Diet’ describes a dietary pattern which, according to the researchers, takes into account both human health and the planet’s carrying capacity – amongst other things, through a significantly reduced consumption of meat and other animal-based foods.

These scientific findings serve as a guide for the Studierendenwerk in the further development of its canteen offerings.

Background

Pilot project in the summer term 2022

In May 2022, the Bonn Student Services Organisation temporarily introduced CO₂ labelling in the Hofgarten canteen as part of a scientifically monitored pilot project*. The labelling was limited to the main ingredients.

Labelling of emissions

For each of the main ingredients on offer, the resulting emissions were estimated and labelled. To this end, the average emissions generated during the conventional production of the respective ingredients were totalled and converted into CO₂ equivalents. The emissions for each ingredient were recorded ‘from farm to gate’, i.e. all emissions arising from agricultural production and from subsequent processing, packaging, preservation and transport were included in the calculation until the ingredient is available for purchase in shops.

A main course with relatively low CO₂ emissions was marked green, the middle category yellow, and main courses with comparatively high CO₂ emissions – in the style of a traffic light – red. On average, the vegan and vegetarian main courses on offer performed better than the meat-based dishes. The calculations were based on the Eaternity database [eaternity.org]. The CO₂ labelling was visible in May 2022 on the online menu for the Hofgarten canteen, as well as on digital display boards and stands at the serving counters.

Scientific analysis

The accompanying scientific study investigated the extent to which CO₂ labelling influences the consumption behaviour of canteen patrons. To this end, till data collected throughout the summer term (April to July 2022) was analysed. A slight steering effect was observed. The consumption of meat dishes fell by approximately five per cent. Furthermore, supplementary surveys revealed that the overwhelming majority of canteen diners would like to see CO₂ labelling introduced on a permanent basis.

*Literature

Schulze-Tilling, A. (2025). The Effectiveness of Carbon Labels (No. crctr224_2025_639). University of Bonn and University of Mannheim. Einzusehen unter: https://www.wiwi.uni-bonn.de/bgsepapers/boncrc/CRCTR224_2025_639.pdf