A recent report from the UN’s Intergovernmental Panel on Climate Change found that unless there are immediate, rapid and large-scale reductions in greenhouse gas emissions, limiting warming to close to 1.5 degrees Celsius or even 2 degrees Celsius will be impossible. Indeed, without swift and major reductions, the report estimates that we will reach or exceed 1.5°C of warming over the next two decades.
Already, the consequences of global warming are being felt to devastating effect, with much of the planet either ablaze, underwater, or scorched by deadly heat waves as mega-fires, extreme flooding, and unprecedented drought wreak havoc across the globe.
With so little time left to change course, scientists are now urging that we must focus on reducing methane emissions as quickly as possible. While carbon dioxide from fossil fuels has received the bulk of attention in past calls for climate action, methane traps significantly more heat than CO2 in the short term. At the same time, it stays in the atmosphere for a much shorter time, leading experts to say that slashing methane is now our single greatest and quickest strategy for slowing down warming by 2040.
Globally, livestock are projected to account for up to 81% of the emissions budget by 2050. The most recent report from the Intergovernmental Panel on Climate Change stresses the urgent need for “rapid, persistent, and substantial” cuts in methane emissions from livestock production, the bulk of which is emitted by grazing animals.
Given the significant contribution of livestock production to GHG emissions — especially methane from grazing animals — the scientific consensus is clear that massive reductions in meat and dairy production play a crucial and unavoidable role in climate mitigation.
Grazing livestock play a major role in driving climate change. Two-thirds of all GHG emissions from agriculture in 2018 came from grazing livestock in the form of enteric fermentation (ruminant animal digestion) and manure. Ruminant animal production, which includes all grazing livestock — cattle, sheep, goats, and buffalo — contributes 80% of total livestock emissions, with cattle alone responsible for 65%.
Methane is one of the fastest-growing GHGs, responsible for 40% of global warming since the Industrial Revolution. Animal agriculture is the largest human-caused source of methane in the United States, with cattle contributing the vast majority of these emissions.
Methane is a far more potent GHG than CO2 because it traps significantly more heat. Methane is 86 times more potent than carbon over a 20-year time frame. For this reason, products from grazing animals, such as beef, cheese and lamb, are ranked as the worst foods for climate.
All grazing livestock, or ruminants, such as cattle, goats, and sheep emit massive quantities of methane as a result of the ruminant digestive system. During this process, known as enteric fermentation, the GHG methane is produced and is emitted primarily through belching.
Grass-fed beef and dairy are even worse when it comes to methane. Cattle consuming a natural diet of grass, hay and other forages produce around four times more methane than cattle fed corn and grains, the traditional diet on intensive industrial or “factory” farms. Harvard researchers have found that shifting to exclusively grass-fed, pastured beef would require 30% more cattle just to keep up with current demand; methane emissions from beef would increase by 43%. This would increase total U.S. methane emissions by approximately 8%.
Scientists have recently discovered that methane levels in the atmosphere are dramatically on the rise. While methane emissions from fossil fuels decreased between the period of 1990 to 2015, methane from enteric fermentation and manure increased 1.5% and 78% respectively.
The Intergovernmental Panel on Climate Change’s previous proposed solutions to limit global warming to 2 degrees Celsius or below have relied on projections that methane levels would drop by 10 parts per billion between 2010 and 2050. Instead, global methane has risen by nearly that much each year since 2014.
Recent research has also suggested that the contribution of methane emissions to global warming is 25% higher than previous estimates. The shorter atmospheric lifetime of methane compared with CO2, along with its greater warming potential, means that reducing meat and dairy consumption and production — especially reducing ruminant animal production — and shifting to more plant-based diets can provide much-needed climate mitigation within a few decades. The reverse is also true: Ignoring or increasing agricultural methane would accelerate the climate crisis.
While ruminant digestion is the largest source of emissions from animal agriculture, manure from grazing animals also results in increased emissions of nitrous oxide (N2O). While there’s much less nitrous oxide in the atmosphere than CO2, it is a powerful GHG, with a warming potential 280 times greater than CO2 over a 20-year time frame.
In addition to its warming impact, nitrous oxide also depletes the ozone layer; it currently ranks as the most significant ozone-depleting substance in the atmosphere. Scientists predict that under a business as usual scenario, nitrous oxide emissions will increase 83% by 2050, underscoring the need for meaningful N2O reductions from agriculture, which is the largest source of human-caused N2O emissions.
The Food and Agriculture Organization notes that in 2018:
Proponents of “regenerative grazing” claim that properly managed grazing can be “carbon-neutral,” offsetting its own emissions by sequestering carbon in the soil. However, numerous studies have debunked this claim, showing that storage of carbon in soils is time-limited, reversible, and that even the most carefully managed targeted grazing systems are significant contributors of GHGs.
Soils reach “carbon equilibrium” within a few decades, after which no more carbon can be drawn down from the atmosphere without a corresponding loss of soil carbon.
Carbon Opportunity Cost
The extensive land use required to produce animal-based foods, especially pasture for grazing animals, also incurs a massive “carbon opportunity cost” due to the foregone potential for carbon sequestration through ecosystem restoration.
Harvard researchers found that shifts in global food production to plant-based diets by 2050 could free up enough land to sequester 332–547 Gt of CO2, with a 66% chance of limiting warming to 1.5 °C. Another major study found that a switch from beef to beans by the U.S. population would free up fields equivalent to 42% of U.S. cropland that could be used for rewilding. A U.N.-backed report published in 2021 concluded that if all pasture around the world that was once forest was returned to its native state, it would store 72 billion tons of carbon — roughly equivalent to seven years of global emissions from fossil fuels.
Deforestation is the second largest anthropogenic source of carbon dioxide emissions after fossil fuel combustion. Global deforestation accounts for almost 20% of all GHG emissions, and the number one driver of deforestation globally is the clearing of land for cattle pasture.
Trees are the world’s largest carbon sinks, sequestering carbon from the atmosphere through photosynthesis. Clearing forests for grazing pasture and to grow livestock feed crops may release as much as 2.4 billion metric tons of CO2 every year.
Earth’s dryland soils contain more than a quarter of all organic carbon stores, as well as nearly all of the world’s inorganic carbon. It’s estimated that 300 million tons of carbon are emitted into the atmosphere each year as a result of dryland desertification, with livestock grazing playing a significant role. Grazing-induced desertification is estimated to release up to 100 million tons of CO2 into the atmosphere annually.
In their report Grazed and Confused, Oxford researchers note: “Systems with grass-fed ruminants can be highly dependent on fossil fuels at levels comparable to intensive pork and poultry production.”
Dietary shifts are a key climate solution. In the largest global analysis ever conducted of the impacts of food and farming on the environment, Oxford researchers found that even the least sustainably grown plant-based proteins overwhelmingly have a much smaller carbon footprint than the most sustainably produced animal-based foods.
Compared to plant proteins such as beans, peas and lentils, beef requires six times more water, 20 times more land, and emits 20 times more GHG emissions per gram of edible protein. Meanwhile, one liter of cow’s milk emits three times more GHGs than one liter of soy milk and requires more than 22 times more water and 12 times more land.
Researchers at Johns Hopkins University recently modeled the climate impacts of different dietary choices and concluded that a plant-based diet is by far the most beneficial, noting 85% fewer GHG emissions compared to the average American diet that is heavy in meat and dairy.
The U.N. notes, “Improving production methods and reducing methane emissions from livestock could reduce emissions by up to 1.44 Gt CO2e per year, but much greater reductions could be achieved by shifting to healthier and more sustainable diets with a higher proportion of plant-based than animal-based foods, which could avoid emissions of up to 8 Gt CO2e each year.”
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