By Jeanne Yacoubou, MS

Researchers concluded in a 2021 article published in the journal Nature Food that global food production contributes 34% of all carbon emissions fueling the climate crisis. What this means is your food choices matter.

Take pizza, for example. According to many surveys, It’s the most popular food in the world.

When given the choice between a vegan pizza or a meat pizza, both loaded with your favorite toppings, you may correctly assume that the carbon emissions associated with a vegan pizza would be significantly less than those accompanying a meat pizza. But how much less? Here, we’ll answer that question.

Greenhouse Gases from Agriculture

Producing all the food components used to make pizza takes energy. That energy source is almost always fossil fuels.

Burning fossil fuels produces carbon emissions, mostly in the form of carbon dioxide (CO₂), a greenhouse gas (GHG). The atmospheric buildup of huge quantities of GHGs in a short time period (since industrialization began in the 1750s) causes more heat from the sun to be trapped closer to Earth rather than reflected back into space. As a result, many countries around the world are experiencing climate crises including massive floods, wildfires, drought, and heatwaves.

Meat and dairy cheese, common components on non-vegan pizza, are the worst food offenders in terms of the amounts of the major carbon-containing greenhouse gases, carbon dioxide (CO₂) and methane (CH₄), released during their production. Growing feed crops that beef cattle and cows eat to produce meat and dairy adds significant amounts of nitrous oxide (N₂O) to the greenhouse gas mix, released mostly from synthetic fertilizers.

Here are some eye-popping statistics related to the world’s crops:

• 77% of the global soybean crop is fed to livestock for meat and dairy production.
• 74% of global maize production becomes animal feed.
• 70% of the world’s freshwater is used for food production.
• 78% of freshwater pollution is due to agriculture.

Each stage of food production – from the farm to your fork – generates carbon emissions from the fossil fuels burned to complete them. For crops, these stages include:

• Preparing the soil
• Planting seeds
• Applying fertilizer
• Harvesting
• Processing
• Packaging
• Transporting

For animals, all of the above applies to produce their foodstuffs. Additionally, carbon emissions are released during:

• Rearing
• Slaughtering
• Processing
• Transporting
• Packaging
• Retailing (refrigeration)

Carbon footprints of food production

The emission of greenhouse gases at each step of food production is cumulative. The sum total of all the stepwise carbon emissions from a particular food’s production is known as that food’s carbon footprint. The lower the carbon footprint of a food, the more sustainable it is. Similarly, the higher a food’s carbon footprint, the greater is the cost to planetary stability.

However, the three major agricultural greenhouse gases are not equally given off during each stage of production. More importantly, they are not equally good at trapping heat. In other words, some hold on to heat longer than others. This complicates precise determinations of the effect of carbon emissions associated with particular foods on global heating. It also makes comparisons between foods’ carbon footprints difficult.

To deal with these problems, researchers devised the notion of carbon dioxide equivalents (CO₂eq).

What is a carbon dioxide equivalent?

To simplify carbon footprint calculations, investigators developed a way to place all greenhouse gases on an equal footing. The reference point for this method is carbon dioxide. Its ability to cause global heating is called its global warming potential (GWP). The Intergovernmental Panel on Climate Change (IPCC) arbitrarily assigned CO₂ a GWP equal to one.

Mathematically, CO₂eq is calculated by multiplying the mass of the emissions of one type of greenhouse gas (usually expressed in kilograms or tons) by its GWP. Total greenhouse gas emissions from the production of a specific food are the sum total of the CO₂eq values of all gases generated from that food during all of its production stages.

However, in reality, GWP is not a fixed value for all time. In the atmosphere, gases naturally decay, but not all at once. And some gases break down more quickly than others. As they decompose, their ability to trap heat is reduced. This means GWP for a particular gas will decrease over time. It also means that GWP is meaningful only when a specific timescale is given. By extension, the total carbon emissions calculated using a certain GWP are relative to its timescale.

Here is a table of GWPs for the three major agricultural greenhouse gases over time taken from the 6^th IPCC Report (2021).

As an example, in a 20-year time frame, methane has a GWP of 81. This means the ability of one kilogram of methane from a belching cow to trap heat is equal to the heat-trapping ability of 81 kilograms of carbon dioxide for the first 20 years after methane’s release into the atmosphere. Another way of looking at it is: if methane has a GWP of 81, then, for 20 years, one kilogram of methane yields 81 times the warming effect of one kilogram of CO₂. On a molecular level, this means that warming due to 81 molecules of CO₂ is equal to that due to a single molecule of methane for the first 20 years it’s floating in the sky.

Methane strategy to reduce carbon emissions fast

Interestingly, carbon dioxide is different from both CH₄ and N₂O because CO₂ persists in the atmosphere far longer, possibly for thousands of years. Methane, on the other hand, is comparatively short-lived, but with a much higher GWP. Its lifetime in the atmosphere is approximately 12 years. Nitrous oxide has an even greater GWP but remains in the atmosphere for 121 years.

The short lifespan of methane suggests an easy way to mitigate the intensifying effects of global heating: reducing methane emissions as much as possible right now. Since animal agriculture is a major source of both CH₄ and N₂O, one strategy to lessen their oversized contribution to the climate crisis is to end the practice of raising animals for meat and milk.

Calculating the Carbon Footprints of Vegan Vs. Meat Pizza

For vegan pizza components such as wheat flour or tomato sauce, carbon footprint calculations involve mostly CO₂ production. If synthetic fertilizer were used to grow wheat, tomatoes, or vegetables, there is nitrous oxide, another GHG with significantly more heat-trapping ability than carbon dioxide, to figure into the carbon footprint calculation.

For vegan ingredients, there is no methane to figure into the total carbon footprint (unless you count the methane produced by rotting plant food waste in a landfill). As a greenhouse gas more potent than carbon dioxide, methane is produced from ruminant animals such as dairy and beef cattle.

Values used in our calculations for the carbon emissions produced by all pizza components comes from two main sources:

1. The 2018 article (https://www.science.org/doi/10.1126/science.aaq0216) by Poore and Nemecek. They analyzed the environmental impacts — including the carbon footprints — of over 38,000 farms in 119 countries producing 40 different commodity food products. Their values reflect global averages. In fact, Poore and Nemecek point out, given the extremely wide variability in farming practices, global averages of environmental impacts are the best indicators of the relative impact — such as the carbon footprint — of a specific type of food product. In this article, we used Poore and Nemecek’s carbon emissions value for wheat.
2. The 2022 article (https://www.pnas.org/doi/full/10.1073/pnas.2120584119) by Michael Clark et al. Like Poore and Nemecek, the researchers calculated environmental impacts of foods. But they focused only on packaged food products you’d find in a grocery store. Most of the values for carbon emissions used here for pizza components have been calculated by the nonprofit Our World in Data based on this research. All CO₂eq are based on a 100-year GWP.

It is not known whether the carbon emission values presented by Our World in Data include those generated from cooking the pizza. It’s unlikely that end-of-life considerations, such as food waste or leftovers going to a landfill, figured into their determination since they vary widely. Readers should be aware that cooking and landfilling have carbon emissions associated with them, too.

However, for our cross comparison of carbon emissions seeking relative differences, it is not needed to know whether the values used include emissions from cooking. We assume all values do or all values do not. In the case where cooking was included, we assume the same cooking method (electric oven, for example) was used. We also assume emissions from disposal to be identical in both the case of a vegan vs. a meat pizza, thereby nullifying any major effect on the final results.

We stipulated that the medium-sized pizzas would be whole wheat since we had an emissions value for it and no other flour. Since we couldn’t find a value for pizza sauce, we included tomatoes and onions in our list of pizza ingredients. These are the major ingredients in pizza sauce. We included enough to make one quart of pizza sauce and assume all is used.

Half of the olive oil was used to make the crust. The remaining oil was used to fry the vegan crumbles, bacon, or ground beef. No values for spices could be found. Since they are used to make both pizzas, their absence from both lists would not affect the final results. We don’t know which type of dairy-free cheese was used. We wrote the authors and have not heard back yet.

Note: Values are approximate due to rounding.

Vegan Pizza Ingredients

Total: 5.53 kg of CO₂eq

Meat Pizza Ingredients

Total: 39.77 kg of CO₂eq

Results on Pizza Carbon Footprints

The VRG used carbon emission data compiled by Our World in Data and based on research by Poore & Nemecek (2018) and Clark et al. (2022) to estimate the carbon footprints of vegan pizza vs. meat pizza. We determined that meat pizza has a carbon footprint roughly seven times greater than vegan pizza.

This result is corroborated with that published by Stylianou et al. (2020). The investigators analyzed carbon footprints of vegetarian vs. meat pizza in several different ways. They found meat pizza’s carbon footprint to be approximately four times higher than vegetarian pizza (with dairy cheese).

Both of these results support the general conclusion of a 2023 article by Scarborough et al. published in Nature Food. As part of the Livestock Environment And People (LEAP) project involving 55,000 people in the United Kingdom, the researchers found that the carbon footprint of a meat diet is more than four times as high as that of a vegan diet.

Conclusions on Pizza Carbon Footprints

Food choices have a direct effect on the climate crisis. By analyzing the carbon emissions associated with pizza, The Vegetarian Resource Group (VRG) calculated that meat pizza has a carbon footprint roughly seven times higher than the carbon footprint of vegan pizza. The difference in the case of pizza is greater than that determined by other researchers.

The contents of this posting, our website and our other publications, including Vegetarian Journal and Vegan Journal, are not intended to provide personal medical advice. Medical advice should be obtained from a qualified health professional. We often depend on product and ingredient information from company statements. It is impossible to be 100% sure about a statement, info can change, people have different views, and mistakes can be made. Please use your best judgment about whether a product is suitable for you. To be sure, do further research or confirmation on your own.