By Seth Millstein for Sentient.
Broadcast version by Eric Galatas for Colorado News Connection reporting for the Sentient-Public News Service Collaboration
In the 10,000 years since humans first developed animal agriculture, livestock farming has become central to modern society. Unfortunately, it's also become one of the biggest drivers of climate change and environmental destruction. Animal farms create a staggering amount of air, water and land pollution, and with the consequences of climate change worsening by the year, addressing the environmental impacts of livestock farming is more important than ever.
Global warming is an enormous part of climate change, but it's not the only part. The concept of climate change encompasses not only rising global temperatures, but all sorts of other changes to the natural composition of Earth and its atmosphere, such as water pollution and land degradation. Here are some of the ways livestock farming contributes to those changes.
But First, a Brief Summary of Greenhouse Gasses
One of the biggest ways livestock farming contributes to climate change is through the emission of greenhouse gasses, which trap heat in the Earth's atmosphere and cause global temperatures to rise. Insofar as livestock is concerned, there are three greenhouse gasses in particular of note.
- Carbon dioxide (CO2): The "main" greenhouse gas, carbon dioxide comprises around 80 percent of all greenhouse gas emissions. CO2 exists naturally in the atmosphere and regularly circulates from the Earth to the air as part of the carbon cycle; however, the burning of fossil fuels and other human activities releases additional CO2, throwing off that cycle and increasing global temperatures. CO2 can stay in the atmosphere for hundreds of years.
- Methane (CH4): Methane only accounts for 11 percent of global greenhouse emissions, and unlike CO2, disappears after a relatively brief 12 years. However, it's much more effective at trapping heat in the atmosphere: over a 100-year period, one pound of CH4 has 28 times the global warming potential as one pound of CO2.
- Nitrous oxide (N2O): Nitrous oxide only makes up six percent of greenhouse gas emissions, and exists naturally on Earth as part of the nitrogen cycle. It remains in the atmosphere for about 121 years on average after it's emitted, and its global warming potential is a whopping 265 times greater than that of CO2 over a 100-year period.
Because there are multiple greenhouse gasses with different warming potentials, greenhouse emissions are commonly converted to and measured in CO2-equivalents, or CO2-eq.
In various ways and to varying degrees, livestock farming emits all of the aforementioned greenhouse gasses. Here's how.
How Livestock Farming Creates Methane Emissions
Livestock are a significant source of methane emissions, thanks to a natural biological process called enteric fermentation. Cows, sheep, goats and other ruminant livestock have microbes in their digestive systems that decompose and ferment the food they eat, and
methane is a byproduct of this fermentation process.
That methane is released into the atmosphere when the animals burp or fart, and it's also contained in their urine and manure. One cow can produce up to
264 pounds of methane every year, and it's estimated that in total, enteric fermentation from ruminant livestock is responsible for 30 percent of
global anthropogenic methane emissions.
How Livestock Farming Leads to Pollution from Manure
Farm animals produce around
450 million tons of manure every year, and figuring out what to do with it is a major challenge for livestock farmers. Some farms
store manure in large piles, landfills or lagoons - known as "settlement ponds" - while others simply dump it onto cropland and use it as untreated fertilizer.
All of these management methods result in the release of methane and nitrous oxide, which manure also contains. When manure is stored in an environment with insufficient oxygen, as is often the case with landfills and lagoons, it undergoes a
process known as anaerobic decay, and releases nitrous oxide and methane into the air as a result. In addition, structural failures or extreme weather events often cause the
manure in settlement ponds to leak into nearby soil and waterways.
When manure is used as fertilizer, it releases nitrogen into the soil. That's the point of fertilizer, as plants need a certain amount of nitrogen to grow. But when farms use this type of fertilization as a disposal method for excess manure, they often over-apply it to the crops in question, which causes the soil to absorb more nitrogen than is necessary.
You might wonder why it matters if soil contains too much nitrogen. There are two intertwined reasons: nutrient runoff and soil erosion.
Nutrient Runoff
Nutrient runoff occurs when rain, wind or other environmental forces disrupt soil and carry it into nearby waterways. When that soil has been fertilized with untreated manure, it pollutes the water in question, both with nitrogen and other toxins that are common in manure, like phosphorus.
Nitrogen and phosphorus both stimulate algae growth, and excessive algae growth in a body of water leads to harmful algal blooms.
As their name implies,
harmful algal blooms have a host of damaging environmental consequences. They release toxins that kill aquatic life and poison the drinking water, which can cause serious illness
and even death in humans. Algal blooms reduce the amount of dissolved oxygen in the water, which aquatic life relies on, and prevent light from penetrating the water's surface, thus choking the life out of coral reefs and other aquatic plants that are crucial to Earth's ecosystems.
Soil Erosion
Nutrient runoff is exacerbated by another consequence of livestock farming: soil erosion. This is when topsoil particles become loosened and detached, which diminishes the quality of the soil and makes it much more susceptible to nutrient runoff.
A degree of soil erosion occurs naturally, but livestock farming greatly accelerates it in a few ways. One is overgrazing, which is when livestock graze on pastures for extended periods without the pastures being given time to recover.
The hooves of cows, goats and other ruminant livestock can erode the soil as well, especially when many of them are grazing in one place.
In addition to making nutrient runoff more likely,
eroded soil is less fertile and can support fewer forms of plant life. It is also worse at retaining water, which can
increase the risk of drought.
Deforestation Due to Livestock Farming
It's impossible to assess the environmental impacts of livestock farming without also discussing deforestation - the practice of permanently clearing out trees from forested land and repurposing the land for other uses.
Humans deforest around 10 million hectares of land every year, and
41 percent of tropical deforestation is carried out to make way for cattle pastures.
Deforestation is a monumentally damaging practice, and exacerbates all of the aforementioned impacts of livestock farming: greenhouse emissions, nutrient runoff and soil erosion.
Greenhouse Emissions Caused by Deforestation
When forested land is cut down, greenhouse emissions increase in two ways - one temporary, one permanent.
Trees absorb and store carbon dioxide from the atmosphere, which makes them an indispensable resource for reducing global temperatures. When they're cut down, however, all of that carbon dioxide is released back into the air. What's more, the absence of trees in a previously forested area means that, for an indefinite period of time, any atmospheric carbon dioxide that would otherwise have been sequestered by the trees remains in the atmosphere instead.
The greenhouse gasses emitted during livestock-driven deforestation, combined with the gasses emitted by livestock farms themselves, account for
11-20 percent of all greenhouse gas emissions worldwide. In the Amazon, which has traditionally been one of the world's largest sequesterers of carbon, so much land has been deforested that the rainforest is in danger of
becoming a net emitter of carbon instead.
Soil Erosion and Nutrient Runoff Caused by Deforestation
In forested land, trees play an important role in protecting and preserving the soil. The canopy they provide protects the soil from the sun and rain, while the trees' roots help hold the soil in place.
Needless to say, clearing all of the trees in a forested area means that the soil doesn't get any of these benefits. As a result, the soil becomes eroded even before any livestock might step foot on it, which in turn increases the likelihood of nutrient runoff and water pollution.
The Bottom Line
The environmental impact of livestock farming can't be ignored. The sector's contribution to deforestation, habitat loss and pollution of all kinds significantly exacerbates climate change. Absent a
significant reduction in global meat consumption, it will continue to present a formidable challenge to the long-term health of Earth and its many inhabitants.
Seth Millstein wrote this article for Sentient.
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