Livestock and manure produce 5,8% of global GHG. But releases from agricultural soils (N2O), crop residue burning, and rice cultivation (all are associated with plant farming) generate 8,9%. So is being a vegetarian really environmentally friendly, climate change-wise?
Gram for gram, meat products produce from twice (comparing fish to wheat) to 150 times (comparing beef to root vegetables) more greenhouse gas emissions than plant products.
In 2020, Our World in Data put together a chart showing total greenhouse gas (GHG) emissions across about 30 types of food, including 11 animal products, in the article "You want to reduce the carbon footprint of your food? Focus on what you eat, not whether your food is local". They considered seven different factors that contribute to GHG emissions:
- Land use change
- Animal feed
Here's the chart from the article showing total kg CO2 equivalent per kg of food product (I highlighted animal products):
What about caloric content?
Comparing food products by mass does ignore the fact that certain types of food have more calories per gram than others. However, the difference in energy density between meat and plant products is an order of magnitude less than the difference in GHG emissions. This U.S. Department of Agriculture study indicates that in the extreme case, an animal product may have 2.5 times more calories per gram than plant products such as whole grains and legumes.
Back to the question
Livestock and manure produce 5,8% of global GHG. But releases from agricultural soils (N2O), crop residue burning, and rice cultivation (all are associated with plant farming) generate 8,9%.
These figures are a reflection of how much of each commodity type was produced in 2016 (the year of the data). If everyone replaced the animal products in their diet with plant products, that 5.8% would go to zero, and the share from agriculture, crop burning, and rice cultivation would increase by substantially less than 5.8 percentage points, since plant products provide more nutritional value with less associated GHG emissions than animal products. Figuring out the exact change will be complicated by the fact that some current plant production goes to produce animal feed, and the need to predict what people would replace meat with.