We have noted elsewhere how difficult it would be to label individual food items with an exact measure of their greenhouse gas emissions.
However the consumer probably does not need very detailed information in order to make informed decisions. All they need to know is the relative emissions produced by different sorts of food. They can then adjust their diet accordingly and thereafter their carbon footprint will automatically be reduced.
More than half of carbon emissions from human food come from animal products, and most beef produces more emissions than other types of animal product.
The following diagram allows the consumer to compare the carbon impact of some different kinds of food.
The diagram is based on the BBC Climate change food calculator which is in turn based upon the paper “Reducing food’s environmental impacts through producers and consumers” by J. Poore T. Nemecek et al, published in Science 360 (6392) 987-992, 01 Jun 2018, doi: 10.1126/science.aaq0216. The BBC has converted Nemecek’s figures to impact per serving size based on serving sizes from the British Dietetic Association (BDA) and healthy diet portion sizes from BUPA.