They are used to power farm machinery, to take foods to market (and home), to store foods awaiting processing and to cook foods. The researchers also tallied methane. Fermentation2 in the guts of ruminant3 livestock — mostly cows — releases this gas. And the scientists calculated the nitrous oxide released during the plowing and fertilizing of crop fields.

All three gases are important. CO2 is the greenhouse gas released in the highest volume. But methane and nitrous oxide stay in the atmosphere far longer than CO2 does. As such, they are more potent,4 molecule for molecule, in warming Earth’s atmosphere.

A computer converted the methane and nitrous-oxide emissions for each person’s diet into its carbon-dioxide “equivalent.” That’s the amount of CO2 needed to warm Earth’s atmosphere by the same amount as the methane or nitrous oxide would.

Switching from meat-rich meals to vegetarian ones would reduce the average meat eater’s CO2 equivalents — also known as its carbon footprint — by 1,230 kilograms (about 1.4 U. S. tons) per year, the new study calculated. Scarborough’s team presented its findings in the July issue of Climatic Change.

HOW THEY CALCULATED FOOD’S ‘CARBON FOOTPRINT’
[10]In the 1990s, a survey asked 65,000 adults what they typically had eaten throughout the past year. Scarborough’s team fed those data into a computer. The researchers also included the amount of greenhouse gases linked with producing nearly 100 common foods. Then the computer matched those greenhouse-gas amounts to the mix of foods each person had reported eating.

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