Vegan Diet: A Sustainable Approach to Climate Change?

The earth’s atmosphere consists of greenhouse gases (GHG) such as water vapor, carbon dioxide, methane, and nitrous oxide which absorb and re-emit infrared energy towards the earth’s surface (called as greenhouse effect). This helps to maintain the global mean surface temperature by 33⁰C, making our planet habitable, without this effect- the earth’s average temperature would be -18⁰C. After the Industrial Revolution, the concentration of CO2 and other trace GHG increased, which amplifies the natural greenhouse effect- thereby resulting in global warming. 

Although raising cattle is now a significant source of protein, it also damages the environment. Around 19-29% of the world’s greenhouse gas (GHG) emissions are attributed to agriculture, while dairy products and the livestock industry account for almost 70% of those emissions. Methane from enteric fermentation, the release of nitrous oxide and ammonia into the atmosphere as well as nitrogen and phosphorus pollution from manure and fertilizer applied to pastures and crops- accounts 78% of the negative impact on biodiversity by agriculture. According to Climate Change 2022: Mitigation of Climate Change, switching to a plant-based diet has a high potential for lowering carbon footprints, combating climate change, and enhancing human health.

By 2050, it’s possible that there will be more than 9 billion people on the planet, which would significantly boost demand for food, particularly protein-rich food and feed. Climate change has significant effects on agriculture and may necessitate continuing adaptation; also, immediate challenges to world food security are crucial for developing countries. More than 113 million people in 53 countries experienced chronic hunger in 2018, as per the Food Security International Network– demanding food and supplies, nutrition, and livelihood support. Due to greenhouse effects, the climate of our world is changing significantly. If greenhouse effects persist in growing, the food shortage will get worse. 

Impact of GHGs on the Economic Sector

Global greenhouse gas emissions are around 50 billion tons per year. The diagram below shows that nearly three-quarters of emissions are caused by energy use, followed by nearly one-fifth by agriculture and land, and the remaining 8% by industry and waste. 

In India, the total GHG emission in 2022 was estimated to be 2.9 Gt CO2, of which 68.7% percent is from the energy sector, followed by agriculture which contributes 19.6 percent, and industrial processes, land-use change and forestry, and waste which contributes around 6.0 percent, 3.8 and 1.9 percent respectively.                                    

Agriculture and GHG emission 

“Agriculture as a sector is responsible for non-CO2 emissions generated within the farm gate by crops and livestock activities, as well as for CO2 emissions caused by the conversion of natural ecosystems, mostly forest land, and natural peat lands, to agricultural land use (FAOSTAT ANALYTICAL BRIEF 18)”. GHG emissions from agriculture (in terms of crop and livestock production for food) are mainly contributed by ruminants such as cattle and sheep (~5.8%), agricultural soils (~4.1%), and rice production (~1.3%).

Since 1990, greenhouse gas emissions from agriculture have risen by 6%. This rise is mostly the result of a 62% increase in the total CH4 and N2O emissions from animal manure management systems, which reflects the rise in the usage of liquid emission-intensive systems over this time.

GHG Emission By Livestock

Around 14.5 percent (7.1 Gt of CO2-equivalent per year) of the total emission are from livestock. Methane (CH4) accounts for approximately 44% of cattle emissions. Nitrous Oxide (N2O, 29%) and Carbon Dioxide (CO2, 27%) make up the majority of the remaining amount. Cattle, raised for both beef and milk produce methane due to enteric fermentation where microbes in their digestive systems break down food thereby producing methane as a by-product. Also, the manure and draft power can produce nitrous oxide and methane when decomposition takes place under low oxygen conditions. In terms of activity, feed production & processing, enteric fermentation from ruminants, and manure storage and processing contribute 45, 39, and 10 percent of total emissions, respectively. On a commodity basis, beef and cattle milk contributes 41 percent and 20 percent followed by pig meat, (9 percent of emissions), buffalo milk and meat (8 percent), chicken meat and eggs (8 percent), and small ruminant milk and meat (6 percent) (Source). Meat (165 CO2-eq.kg)  and milk (112 kg CO2-eq.kg) from small ruminants come in second and third, with beef having the greatest emission intensities (nearly 300 CO2-eq per kilogram of protein produced). Since beef and lamb tend to have a high carbon footprint, consuming less is an effective way to reduce the emissions of your diet.

How can we reduce emissions?

Available mitigation options discussed in FAO’s assessment include:

• For ruminants, adopting improved feeds and feeding methods can lessen the quantity of methane (CH4) and nitrous oxide (N2O) released during the digestion and decomposition of manure.
• Reducing herd numbers (i.e., using fewer, more effective animals) through improved breeding and animal health treatments would also be effective. The management of manure, which enables the recovery and recycling of nutrients and energy, as well as the deployment of energy-saving technologies, all play a part.
• Better management of grazing lands could enhance productivity and help to establish carbon sinks which will potentially help offset livestock sector emissions.

• “Precision feeding,” breeding, and better animal health care approaches can decrease emissions from feed production and manure management in monogastric agriculture (chicken and pig farming). Additional reductions might be possible by switching to feed sources whose production requires less energy and to more eco-accommodating sources

Is a plant-based diet, a better solution to reduce GHG Emissions?

Based on EU-Horizon 2020 project Protein2Food (AMD-635727), plant-based proteins are more efficient than animal-based products in relation to GHG emissions. A recent study conducted by Zhongxiao Sun et.al (2022) concluded that “dietary change could reduce annual agricultural production emissions of high-income nations diets by 61% while sequestering as much as 98.3 (55.6–143.7) GtCO2 equivalent which is equal to approximately 14 years of current global agricultural emissions until natural vegetation matures”. 

Around 80% of the agricultural land (~35% of the total habitable land in the world) is used for animal grazing. According to scientists at Leiden University, if developed countries change the dietary plan from animal-based to plant-based, less land is required to grow food and vast areas can be reverted to their natural state which will increase carbon sequestration. Converting former cropland and pastures to their natural state would remove ~98.3 billion tons of CO2 from the atmosphere which helps the planet from warming more than 1.5 degrees Celsius.

Andreas Detzel et.al (2021), conducted a life cycle assessment (LCA) on animal-based foods and plant-based protein-rich alternatives. From his study, The optimal vegetable (VMA) created from faba bean protein and amaranth (variant 3) has a carbon footprint of 130 g CO2 equivalents per 100 g of food, whereas the carbon footprint of 100 g of chicken meat is 232 g CO2 equivalents which are approximately two to three times greater than VMA extrudes. The carbon footprint of cow’s milk is three to almost four times more than that of milk derived from lentil protein.

It is obvious that the transition to sustainable food systems will not take place without a change in people’s diets as global food production represents the biggest burden put on the planet by humans. Despite the advantages for both health and the environment, it is very challenging to convince consumers to switch to a diet that includes little or no animal products, and the average amount of animal products consumed globally per person has only gone up.

(By Suja Mary James)