Sources & references

Every number is cited. Food, transport and home energy lean on two open government/academic datasets; the made-object rounds (things, clothing) and the waste round come from published life-cycle studies, cited per item. Where the studies genuinely disagree, the value is marked an estimate. Here is the full provenance, by category.

Food

Our World in Data, from Poore, J. & Nemecek, T. (2018), “Reducing food's environmental impacts through producers and consumers”, Science 360(6392), 987–992. Global averages of kg CO₂e per kg of food across the whole supply chain. Licensed CC-BY 4.0.

Fridge & pantry

ADEME AGRIBALYSE 3.2 (2025), the French public food life-cycle database, via impactco2.fr. Licence Ouverte 2.0. A second food set, measured on a different basis to Our World in Data, so it runs as its own round and isn't ranked against the OWID numbers. Some items (a flown-in mango, an avocado) bake in transport to a French/EU shelf.

Transport

UK Government GHG Conversion Factors for Company Reporting (DEFRA / DESNZ, 2022), per passenger-km at average occupancy, applied over 100 km. Open Government Licence v3.0.

Home energy

UK Government GHG Conversion Factors (DEFRA / DESNZ, 2024): grid electricity at 0.207 kg CO₂e per kWh and natural gas at 0.183 kg CO₂e per kWh, multiplied by the kWh each action uses. Open Government Licence v3.0.

Everyday choices

Built from the two datasets above, applied to one real-world amount each (a cup of coffee, a 150 g serving, a 100 km trip). Food amounts use the Our World in Data factors; travel amounts use the DEFRA passenger-km factors.

Things you buy & clothing

The cradle-to-gate cost of making one item, cited per item from published life-cycle work: peer-reviewed studies (e.g. MIT footwear 2013, the 2012 paperback-book LCA, display LCAs), industry product reports (Apple iPhone, Trek bicycles, Levi's jeans), Carbonfact garment benchmarks (2024), and government carrier-bag LCAs (UK Environment Agency 2011, Danish EPA 2018). Garment and furniture figures vary by fibre, allocation and method; the softer ones (a wool suit, a backpack) are flagged as estimates.

Waste & recycling

US EPA Waste Reduction Model (WARM v15, 2019), landfilling pathway. Public domain. Values are kg CO₂e to send 1 kg of a material to landfill (end-of-life only, not manufacturing). US landfill assumptions, so not directly transferable elsewhere.

Shock comparisons

Cross-category rounds that combine the sources above at illustrative quantities we chose. You are ranking those amounts, not the items in the abstract.

All cited data is used with attribution under its licence; the datasets remain the property of their authors. Spotted a number that looks off? Tell us with a source and we'll fix it.