Our diet is an important driver of climate change: 35 percent of all man-made greenhouse gas emissions are caused by the food industry. A study has now quantified that foods of animal origin account for the largest share at 57 percent. Plant-based foods account for 29 percent and other uses such as rubber and cotton for 14 percent. Data from more than 200 countries for 171 crops and 16 animal products were taken into account.
In the course of the last century the world population has quadrupled and the proportion of animal products in the diet has increased. More and more land is therefore required for the production of food, for example to grow plants for human consumption and as animal feed, and to keep animals such as cattle, pigs and poultry. The production and transport of food releases large amounts of greenhouse gases such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) – with serious effects on the climate. A team led by Xiaoming Xu from the University of Illinois in the USA has now quantified the contribution made by the individual food sectors.
Data from over 200 countries
For this purpose, the researchers created a freely accessible database with data from over 200 countries, which allows precise estimates of how much carbon dioxide, methane and nitrous oxide are produced by plant and animal foods. To do this, they used data from around 2010. “This is the most recent period for which the necessary data is available, particularly raw material balances for grain and livestock and feed data,” the researchers say.
For their calculations, they took into account various greenhouse gas emissions along the production chain: conversion of areas, for example from forest to arable land, fertilization of food and fodder crops, livestock farming, as well as the processing and transport of food. In addition to CO2 emissions, they also included the greenhouse gases methane and nitrous oxide, converting their effect into CO2 equivalents. “Although CO2 are the most important and most discussed greenhouse gas emissions, methane produced by rice cultivation and animals and nitrous oxide from fertilizers are 34 and 298 times more potent than CO2 when it comes to trapping heat in the atmosphere,” explains Xu.
Greenhouse gas emissions quantified
The calculations show that the food sector is responsible for greenhouse gas emissions of 17.318 billion tons of CO2 equivalents each year, 61 percent of which is carbon dioxide, 27 percent methane and twelve percent nitrous oxide. The largest share is accounted for by animal products: 57 percent of the emissions are caused by the keeping and utilization of farm animals, including the cultivation and transport of feed. According to the calculations, cattle are particularly harmful to the climate: 25 percent of all greenhouse gas emissions from animal-based foods are attributable to beef, and another ten percent to dairy products.
Plant-based products, on the other hand, are only responsible for 29 percent of food greenhouse gas emissions. The management of agricultural land and the conversion of areas from forest to arable land have the greatest influence. Rice is responsible for the most greenhouse gas emissions (12 percent) among plant-based foods, because microorganisms produce large amounts of methane in the flooded rice fields. The remaining 14 percent of greenhouse gas emissions from the food sector come from non-food products, including cotton and rubber. However, since these goods also contribute to land use, the researchers included them in the analysis.
Make future nutrition climate-friendly
A country comparison shows: In almost all regions of the world, animal foods account for the largest share of greenhouse gas emissions. The exception is the region of South and Southeast Asia, where a lot of rice is grown. Here, plant-based foods have the largest share of emissions. In absolute terms, South and Southeast Asia have the highest food-related greenhouse emissions worldwide, but the lowest per capita along with the Middle East and North Africa. South America has the highest per capita food greenhouse gas emissions and the second highest in absolute terms. Here animal foods make up by far the largest share. Europe is in the middle of the field, with emissions from animal products clearly predominating here as well.
“We anticipate that population growth will drive the expansion of subsectors of the food industry, including crops and livestock, as well as the transportation and processing of products, irrigation, and the use of fertilizers and pesticides,” said Xu’s colleague Atul Jain. In view of this, it is particularly important to shape future world nutrition also taking into account the climatic consequences. “The development of climate protection strategies must be based on accurate estimates of greenhouse gas emissions from all sources,” said Jain. The researchers’ model can help here. “Positive effects can also be recorded, for example when areas that become free when we switch from an animal to a plant-based diet are reforested,” the researchers say.
Source: Xiaoming Xu (University of Illinois, USA) et al., Nature Food, doi: 10.1038 / s43016-021-00358-x