How Can We Estimate the Greenhouse Gas Emissions Associated With our Diet?

Based on current estimates, agriculture is responsible for 10%-15% of global greenhouse gas emissions (GHGE). But some foods requires less GHGE to grow, package, and transport than others. One way to compare the GHGE associated with eating a particular food is to estimate its carbon intensity (CI)—the GHGE resulting from the production and post-production activities required to deliver you 1 kilogram of a particular food.

The calculator estimates the CI of an entire diet. (See below for more details on how the estimate is made.)  The resulting number—the carbon intensity of the diet (CID)—is therefore an estimate of the total GHGE associated with the particular diet. The units of the output are grams CO2e per food calorie (GHGE is typically measured in “carbon dioxide equivalents,” or CO2e), enabling one to estimate the total GHGE associated with a diet by multiplying the CID number by the total calories in the diet. Here’s an example.

Example

Suppose a diet consists of 10% beef, 10% chicken, 15% dairy, 40% grains, 5% legumes, and 20% vegetables. Then its CID number (the output of the calculator below) is 3.81 grams CO2e per calorie. For a typical 2,000 calorie daily intake, this would result in 3.81(2,000)=7,620 grams (7.62 kg) of CO2e GHGE. That’s equivalent to burning 7.3 pounds of coal, and that’s only for one day and one person! 

Okay, now on to the calculator. Feel free to change the cells in green to whatever percentages (expressed as a number between 0 and 1) you’d like. Be aware though: the percentages you input must add to 1.

How Was This Calculator Created?

In 2011 the Environmental Working Group published a comprehensive analysis of the GHGE by food category (available here). Using these values, along with the nutritional information of representative foods in each category (see the chart below), yields the following CID equation:

where b, c, d, g, l, v are the percentages of beef, chicken, dairy, grains, legumes, and vegetables in the diet, respectively (it is assumed that these percentages add to 100%).