How this calculator works
Meat carries a larger footprint than plants because animals convert feed into meat and lose most of the energy in the process, and because ruminants such as cattle and sheep also produce methane. The figures here are global averages per kilogram of food product from the largest meta-analysis of food life cycle studies: beef from the beef herd 99.5 kg CO2e per kg, lamb 39.7, pork 12.3, poultry 9.9 and farmed fish 13.6. Land use follows the same order, from 326 square metres per kilogram of beef to 12 for poultry and under 4 for farmed fish. Multiplying by the amount eaten in a week and by 52 gives the annual total. The figures include production, processing and transport to the point of sale, but not cooking, refrigeration at home or wasted food, so the real footprint is somewhat higher.
Formula
annual kg of a meat = weekly kg x 52, or weekly servings x serving weight / 1000 x 52. emissions = sum of annual kg x kg CO2e per kg for each meat. land = sum of annual kg x square metres per kg. The savings figure is the cut percentage times total emissions.
Worked example
Four hundred grams of beef, 200 g of pork, 400 g of chicken and 100 g of fish a week. Beef is 0.4 x 52 = 20.8 kg a year and 20.8 x 99.5 = 2,070 kg CO2e. Pork is 10.4 kg and 128 kg CO2e, chicken 20.8 kg and 206 kg CO2e, and fish 5.2 kg and 71 kg CO2e. The total is about 2,475 kg CO2e a year, with 84 percent from beef.
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Frequently asked questions
Why is beef so much higher than chicken?
Cattle are ruminants and produce methane, they eat far more feed per kilogram of meat, and they occupy more land for longer. Chicken converts feed efficiently and produces no enteric methane, so its footprint per kilogram is about a tenth of beef.
Does grass-fed beef have a lower footprint?
It can store carbon in pasture, which some studies credit as a reduction, but grass-fed animals grow more slowly and produce more methane per kilogram. The evidence is mixed, and the global average here does not assume a particular production system.
Is farmed fish always better?
It depends on the feed. Carnivorous farmed fish such as salmon eat fishmeal and oil, which carries a footprint. Filter feeders such as mussels and oysters are among the lowest-impact animal proteins. The figure here is an average for farmed fish.
What should I swap to?
Replacing beef with beans, peas, lentils or tofu cuts the footprint by roughly a factor of 10 to 50 per kilogram of protein. Poultry and pork are lower-carbon than beef but still far above pulses. The savings figure shows what a uniform cut would do; a targeted cut to beef usually saves more.
Sources
- Poore and Nemecek (2018), Reducing food environmental impacts through producers and consumers, Science
- Our World in Data: environmental impacts of food production
- Environment and Climate Change Canada: emission factors and reference values for greenhouse gas quantification (national inventory edition, updated annually)