There isn’t any specific scientific consensus on the precise impact of livestock on the climate. It is a contentious issue, partly because it’s so difficult to measure. We can say, however, that the impact is likely colossal.
Moving towards plant-based diets will not, by itself, solve the climate problem. We still need to end our reliance on fossil fuels. However, it is necessary to solve the climate problem.
Of course, just because something is “unsustainable” doesn’t mean we can’t do it anyway! Long before it becomes physically impossible to raise more cattle, though, we encounter increasingly unpleasant consequences, such as soil erosion, groundwater depletion, and rising medical costs. Halting the runaway consequences of livestock agriculture requires a sustainable, steady state economy, encompassing sustainable scale in the livestock industry along with all other sectors.
But let’s focus on one particularly nasty consequence of livestock production: climate change. The scientific community overwhelmingly acknowledges the reality and urgency of climate change. The American public also acknowledges it, though less overwhelmingly.
However, there is much less discourse—scientific or public—about livestock’s contribution to the problem. It is a contentious topic for complex reasons. And while mainstream science focuses almost exclusively on direct emissions from livestock production, there may be more to the livestock-climate story.
A Complex Problem
A key reason livestock’s impact on the climate is hotly debated is that it is difficult to assess land-use impact.
The main human use of land is for agriculture. Agriculture dwarfs urban development, roads, and buildings in the sheer area of land involved. And of that land, about 80 percent is for livestock production. So if we’re talking about land use, for the most part we’re talking about livestock.
Land use affects the number and type of plants and animals, and plants and animals are key factors in the natural carbon cycle. Plants absorb carbon dioxide (CO2), and animals respire CO2. Due to human land use, plants are decreasing, and animals are increasing, in terms of biomass. This creates an imbalance that impacts the amount of CO2 in the atmosphere.
To measure these impacts, scientists are turning to the relatively new concept of “carbon opportunity cost.” In the livestock-production context, this refers to the additional carbon the land and its vegetation would absorb if not converted to grazing land or cropland for livestock feed. This concept can also be applied to cropland used to feed humans directly. This would enable comparison between the carbon opportunity cost of producing the same number of calories or grams of protein via animal- versus plant-based foods. Such analyses get complex quickly, especially when one considers the drastic regional differences in livestock and crop productivity.
A Contentious Problem
Methane is another complex and contentious factor regarding livestock production’s impact on the climate. Agriculture is the single largest anthropogenic source of methane, and most of that is from livestock. But there is no agreement on the best way to assess methane’s impact.
Methane has a much greater impact than CO2 in terms of its warming potential, but it also breaks down fairly quickly in the atmosphere. The net impact depends on the time frame we choose, and scientists and policymakers have not agreed on what time frame is most appropriate.
Finally…politics. The Food and Agriculture Organization (FAO) of the United Nations is influenced, if not effectively controlled, by the livestock industry. In 2012 they announced an official partnership with the meat and dairy industries.
Even basic data like the number of cows is often contested. In the early 2000s, many non-governmental organizations reported double the number of cattle that the FAO did. Even the FAO’s own data on poultry production differs from report to report by a factor of two. Their April 2003 Food Outlook puts the amount of poultry produced in 2002 at 72.9 million metric tons, while Livestock’s Long Shadow provides a figure of 33.0 million metric tons.
President Trump has exacerbated the problem with his attacks on scientific research, but the lack of solid livestock data pre-dates the Trump Administration by decades.
What’s with the Carbon Cycle?
To untangle the complexity surrounding land use, an overview of the short-term carbon cycle helps.
CO2 is circulating into and out of the atmosphere due to natural processes. Most emissions are not human-caused; anthropogenic CO2 emissions amount to only three percent of the emissions from natural sources. This is not three percent of CO2 in the atmosphere, but an extra three percent of CO2 emissions. In the natural world, carbon sources (such as decaying organic matter and animal respiration) are roughly counter-balanced by carbon sinks (soils, oceans, and photosynthesis).
Photosynthesis—through which (among other things) plants absorb CO2 from the atmosphere and emit oxygen—is a key process in the short-term carbon cycle. When plants die, microbes in the soil consume them and release CO2 back into the atmosphere. However, some of the carbon from plant matter is stabilized in the soil, as well, for long-term storage.
Earth’s soils hold more carbon than its atmosphere and vegetation combined. Oceans are also key in the short-term carbon cycle. They are currently massive carbon sinks, but their ability to absorb CO2 is limited.
Historically, these processes—photosynthesis, decay, respiration, and absorption and emissions from oceans—have typically balanced each other out. There are also long-term carbon cycles. The ice-age cycle, and the even longer-term geological carbon cycle, can last hundreds of thousands or millions of years. For our purposes, we can ignore these. (For the very long-term thinkers: Watch out for that next ice age.)
Carbon Opportunity Cost
The most obvious way to disrupt the short-term carbon cycle is to put extra CO2 into the atmosphere, such as by burning fossil fuels. But a different way is to reduce the amount of photosynthesis. Let’s consider the very real example of someone burning the Amazon rainforest to create grazing land in Brazil. The direct CO2 emissions can be considerable.
But the burning itself is a one-time event. What about next year? Left to itself, in many cases the forest would begin to regrow, drawing CO2 out of the air and incorporating the carbon into tree growth. But in this case, cattle grazing obstructs reforestation.
Of course, plants still grow on pastureland. Forests may have immense carbon-storage capacity, but how do their rates of ongoing carbon sequestration compare with grazing lands? It depends. Grasslands with deep root systems can be powerful sequesterers, and cattle grazing can degrade or augment that power, depending on management practices.
In our Brazilian-Amazon example, the grazing land would almost certainly have a lower rate of carbon sequestration than the forest it replaced. That’s because the Brazilian Amazon biome has the highest carbon sequestration potential of all the world’s forests. It is also one of the world’s most deforested biomes, currently, though forests have long been victims of economic activity.
Humans have reduced the number of trees on Earth by almost half. Yet, forests still constitute 80 to 90 percent of Earth’s plant biomass. Though difficult to measure across varying habitats and management practices, the impact of replacing these invaluable carbon sinks with pastureland could be immense.
And yet, forests aren’t the only ecosystems being converted into grazing land. Likely due in part to the attention forests receive, natural grasslands and wetlands are being lost to agriculture at a rate four times higher than forests. Over half of this conversion has been to raise livestock or their feed. This phenomenon is happening on such a large scale, that it would be foolish not to seek to better understand its carbon opportunity cost.
More Animals, Fewer Plants
Even before trying to estimate carbon opportunity costs, there are two reasons to believe it’s quite big: Large mammal biomass (and total animal biomass) is substantially increasing, and plant biomass is crashing. This is despite declines in populations of wild large animals, or megafauna.
North America provides a tragic example of these declines. The American bison population plummeted from 60 million in the 1850s to only a few thousand in the 1880s. Globally, elephant (carbon) biomass declined an estimated 90 percent in the 20th century. 70 percent of the world’s wild megafauna species are declining in numbers.
But increases in humans and our livestock have far outstripped decreases in wild megafauna. Cattle (carbon) biomass increased 250 percent in the 20th century. In 2000, humans and our domesticated animals constituted an incredible 97 percent of all terrestrial animal (including human) biomass. And about two-thirds of large-animal biomass is livestock, which has about double the mass of the human population! The large animals on Earth are now mostly cows and people.
As bad as the increase in animal biomass—and resultant increase in respired CO2—is, it’s gone hand in hand with another, perhaps more alarming, biological problem. In a “full world,” more land dedicated to animals means less available for plants. Phytomass (plant biomass) has dramatically declined under human influence. Vaclav Smil at the University of Manitoba estimates it has declined by half in the last 5,000 years.
This is corroborated by a more recent study. Researchers estimated that, without human influence, Earth would contain 916 billion metric tons of plant matter. In reality, it only contains 450 billion. How do you think the destruction of half of Earth’s plant life might impact photosynthesis and, in turn, CO2 levels?
To be clear, not all of this plant destruction has been for the sake of livestock production. But recall that agriculture dwarfs other human land uses and livestock production dwarfs other agricultural land uses. Sure, producing less in animal products would mean producing more in plant products for human consumption. But it takes an estimated 50 to 100 times more land to produce a gram of protein from beef compared to peas or tofu.
Of course, not all land is suitable for crops. But when some researchers say plant-based diets could cut agricultural land use by 75 percent, it’s time to rethink how we’re using Earth’s carbon sequestration potential.
Measuring the Impact
We have good reason to believe the climate impact of expanding animal biomass and decreasing plant matter is large. Yet some experts steadfastly ignore the idea of carbon opportunity cost. The FAO made no mention of it in their 2024 report. This may be due to the involvement of the meat and dairy industries in the FAO. These industries have spent millions to influence public and scientific opinion and have plausibly been accused of hijacking the FAO.
There’s no consensus in favor of the FAO’s figures on livestock’s climate impact. According to some researchers, the FAO figures are substantially understated and we must take more drastic action than they imply. Measuring carbon opportunity cost is hard, but some scientists are attempting to provide alternatives to the FAO figures.
Searchinger et al. concluded, “…standard methods for evaluating the effects of land use on greenhouse gas emissions systematically underestimate the opportunity of land to store carbon if it is not used for agriculture.” In a follow-up report, they incorporated these opportunity costs into their estimates: “…western diets overall have much higher greenhouse gas costs than conventionally estimated.” They also found “that the total greenhouse gas costs of beef and dairy globally are 3–4 times those found by the Food and Agriculture Organization…shifting consumption of ruminant meat and dairy to other foods would reduce emissions [from western diets] by 70 percent.”
Hayek et al. concluded a worldwide move towards plant-based diets would sequester an additional 152.5 billion metric tons of CO2. Eisen and Brown published an article for which the title tells it all: “Rapid global phaseout of animal agriculture has the potential to stabilize greenhouse gas levels for 30 years and offset 68 percent of CO2 emissions this century.”
Factoring in carbon opportunity costs only adds to the evidence about direct emissions that has led many experts to back immediate action. A 2024 survey of climate scientists and food experts revealed general agreement that livestock emissions must peak in 2025 and “fall rapidly” in high-income and middle-income countries.
To be clear, to stop climate change this shift toward plant-based diets needs to be in addition to, not instead of, phasing out fossil fuels.
But we will only be successful if we restore populations of the plants that pull CO2 from the air. To restore those populations, we must give back some of the land we’ve claimed for ourselves and our livestock. That’s a key ingredient of a steady-state economy: leaving enough resources for the economy of nature, on which the human economy depends, to thrive. Shifting towards plant-based diets is one small price to pay—one that can have myriad benefits for the consumer—for true sustainability.
