Carbon dioxide, methane and nitrous oxide are the so called greenhouse gasses (GHG). In fact, they absorb the infrared (IR) radiations coming from the sun and this is why they are responsible for the global raising temperatures. Contrary to popular beliefs, atoms and molecules, which GHG are made of, don’t have fixed positions but they can move. For example, atoms can vibrate along chemical bonds. GHG like to sunbathe and the effect of that long exposure to sunshine is that atoms vibrate faster along the bonds. This is how GHG basically trap heat by speeding up the frequency atoms move across a chemical bond.
The invisible motion of still objects — Ran Tivony — YouTube
Molecules like to sunbathe while human beings enjoy vast consumption of food. As the sunbathing, this has also a negative effect on the planet. In fact, modern diets and the whole business of food production make up to a large fraction of GHG emissions. [1] To break it down: carbon dioxide is the by-product of the use of machineries, transportation of goods and supply chain. Methane is generated mainly from animal farming and cultivation of rice. Nitrous oxide is released into air by using fertilizers, farming of ruminants such as cattle, sheep, goats and deer and rangeland. Despite this dramatic scenario, only one-third of countries have agriculture and farming mitigation measures in place to meet the criteria agreed in the Paris Agreements. [2]
A new publication titled Future warming from global food consumption was published last March in Nature Climate Change to better understand the problem and offer solutions. [3] As a starting point, the authors selected 94 food items and evaluated the individual contribution of carbon dioxide, nitrous oxide and methane each food item gave. Then, they evaluated the food available for consumption for 171 countries using the Food and Agriculture Organization (FAO) food balance sheets. [4] By combining food consumed by the 171 countries and the single contribution to GHG emissions, they made some estimates on the current state of global emissions. What they found is extremely concerning. 4860 Million tonnes (Mt) of carbon dioxide, 151 Mt of methane and 9 Mt of nitrous oxide are currently emitted in the atmosphere due to worldwide food consumption. Without any mitigation, the authors projected an increase of between 0.7 (± 0.2) and 0.9 (± 0.2) in global temperatures by the end of the 21st century.
What did the author offer as evidence-based solutions?
To begin with, they divided food items into 12 food groups: grains, rice, fruit, vegetables, ruminant meat, non-ruminant meat, seafood, dairy, eggs, oils, beverages and other. Then, they moved to understand the contribution each group gave in terms of GHG emissions. They found that consumption of dairy and meat was responsible for more than half of the warming. Of the other food groups, rice contributed to a large fraction of warming (19%), whereas vegetables, grains, seafood, oils, beverages, eggs, fruit, and all other uncategorized food items each contributes 5% or less.
With this set of data in hand, they identified 3 major areas of improvement: optimisation in production practises, behaviour changes towards healthier diets and decreasing food loss along the supply chain.
Improvements to production practices of ruminant meat, dairy and non-ruminant meat could potentially decrease GHG emissions of roughly 35, 30 and 10% respectively. Those mitigations primarily focused on reducing the amount of methane and nitrous oxide emissions. To reduce methane emissions, the author suggested feeding animals with long fatty acids such as sunflower oil, linseed fatty acids, whole grains and forage legumes as an alternative to current diets. [5] On the other hand, to lower nitrogen oxides emissions, they proposed the use of nitrogen balance spreadsheets to evaluate inputs vs outputs of nitrogen, using manure and legumes as renewable nitrogen sources and introducing winter cover crops to capture residual nitrogen and reduce the risk of soil erosion. [6]
Next, they focused on introducing healthier diets. In this regard, the Harvard Medical School recommends a diet low in meat , saturated fats and cholesterol but high in protein. Specifically, they suggest eating red meat, beef and pork about one serving per week, and limit fish, poultry and eggs up to two servings each per day. If these dietary changes were implemented globally, warming due to food consumption could be decreased by 0.19 °C by the end of the century.
Finally, the author highlighted the potential for decreasing food loss and waste at the farm, transport, retail, and consumer level to mitigate GHG emissions. Using the United States 2030 Food Loss and Waste Reduction Goal [7] in combination with the FAOSTAT’s food balance sheets [4] to understand the size of food waste, they estimated a decrease in global temperatures from 0.03 up to 0.1 °C.
As global population, we had already reached more than 1 °C temperature increase above preindustrial levels by 2021 [8]. Without mitigations, this additional warming from food consumption alone is enough to surpass the 1.5 °C target and approach the 2 °C threshold established by the Paris Agreement. It is clear that succeeding in this global afford to mitigate global warming is a multifaced afford and needs the implementation of new legislations as well as behavioural changes. These go hand in hand and they cannot be mutually exclusive. It’s a cumulative endeavour in changing and optimising animal farming, transport of good, production and diets while avoiding food loss along the supply chain.
References:
[1] Food systems are responsible for a third of global anthropogenic GHG emissions. Nat. Food 2, 198–209 (2021).
[2] World Energy Outlook 2018 (International Energy Agency, 2018)
[3] Nature Climate Change, 2023, 13, 297–302
[4] FAOSTAT (Food and Agriculture Organization, 2019)
[5] Renew. Sustain. Energy. Rev., 2012, 16, 5059–5070
[6] BioScience, 2018, 68, Pages 194–203
[7] United States 2030 Food Loss and Waste Reduction Goal (United States Environmental Protection Agency, 2022).
[8] IPCC Climate Change 2021: The Physical Science Basis (eds Masson-Delmotte, V. et al.) (Cambridge Univ. Press, 2021)
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