The environmental impact of what you eat and how much it matters.
In Part 1, we covered what trophic levels are and how different organisms obtain energy to live. Now, we will look at our personal trophic levels and determine how our food choices impact resource use and environmental health. Can our personal food choices really make a difference? We will answer this question by looking at land use, fresh water use, greenhouse gas emissions, and eutrophying pollution.
Food is energy. It's chemical energy that we humans need to power our biological systems to survive and thrive. At the most basic level, all of the resource costs of food production increase as we eat higher on the trophic pyramid because primary energy cost goes up about tenfold at each level. So, while eating primary producers (plants) is generally less resource-intensive than eating primary consumers (animals), there are nuances to consider. In the following analysis, we will discuss resource use per 1000 kilocalories since each person's energy requirement is in kilocalories, not food weight.
Land Use
About half of the world's habitable land is used for agriculture. 80% of that land is used to raise animals for human consumption, but those animals only provide 17% of the calories that humans eat. Humans get the remaining 83% of calories from plants, which only require 16% of agricultural land.
If humans only ate meat from the current mix of livestock, we would need 224 million square kilometers of land to raise those animals—much more than the total amount of land on Earth. Even if we cut down every last acre of forest and used glaciers and deserts for meat production, we still would not be able to feed the 8 billion people on Earth on a carnivore diet. If we took all of Earth's agricultural land and used it for meat production, we could feed a population of only 1.7 billion people—we currently have 8 billion, and rising.
If humans only ate plants, 10 million square kilometers of land would be needed to grow those plants for all human consumption. That would free up 78% of the land currently used for food production. If we did use all of Earth's agricultural land to grow plants for human consumption, we could feed a population of 38 billion people. (That's only considering land use. A human population that large is nowhere near sustainable.)
According to the U.S. Department of Agriculture, about one-third of Americans' calories come from animal foods. If the world adopted the American diet, we would need about 81 million square kilometers of agricultural land, which would require cutting down 88% of Earth's remaining forests.
Cows and sheep require by far the most amount of land to produce a calorie of food, followed by pigs and poultry. Almost all plant foods require a small fraction of the land that animal foods do. Beef, for example, requires 92 times as much land as tofu (from soybeans) for the same amount of calories and 74 times as much land for the same amount of protein.
On average, animal foods require 18 times more land than plant foods. Alternatively, plant foods require only 5.7% of the land as animal foods do.
Fresh Water Use
As a civilization, we are using water at an increasing rate. Our rate of groundwater extraction now exceeds nature's ability to replenish it. Using less water is critical to our long-term viability.
70% of global freshwater withdrawals are used for agriculture. Among the foods we eat, the highest fresh water users are shrimp and fish, followed by dairy, beef, and pork. Poultry is the most water-efficient meat product. Among the plant foods, nuts and rice use the most fresh water, and potatoes, tofu, and corn use the least.
On average, animal-based foods use about 4 times the amount of fresh water as plant foods.
Greenhouse Gas Emissions
Food production accounts for 26% of global greenhouse gas emissions. Perhaps surprisingly, food processing, transport, packaging, and retail accounts for a small fraction of the emissions from food production. Most emissions come from farming, animal feed, and land use change. So what we eat has a much more significant effect on emissions than where it comes from, i.e. local beef is much worse than bananas shipped across the world.
Beef creates the most greenhouse gas emissions by far, mostly from cows producing methane and the land use change required to raise them. As we saw in part 1, cows are inefficient at converting their food into edible meat for humans. They require a lot of feed, which requires a lot of native forest and other land to be cleared to grow that feed. Beef results in 7 times the emissions of poultry, 31 times the emissions of tofu, and 96 times the emissions of corn.
Across the board, animal-based foods create way more CO2 and equivalent emissions than plant-based foods. The animal foods with the lowest emissions are poultry and eggs.
On average, animal-based foods tend to create 10-50 times the greenhouse gas emissions of plant foods.
Pollution
From pesticides, fertilizer, and animal waste, pollution from food production's waste streams comes in many forms and is hard to measure precisely. One of the most prevalent forms of pollution is fertilizer runoff, which causes eutrophication. Synthetic fertilizers containing nutrients, such as nitrogen and phosphate, wash off agricultural land and into waterways where they cause algal blooms. That reduces the oxygen in the water and kills fish and other marine life, setting off a harmful chain reaction in ecosystems. 78% of global ocean and freshwater eutrophication is caused by agriculture.
Shrimp and fish are large offenders when raised in large concentrations in fisheries, where their nutrient-rich waste is directly released into the surrounding water. Beef production, no surprise, contributes highly to eutrophication, too. Even disregarding the direct cow waste washing into waterways, the fertilizer runoff from growing all the food for cows is significant.
Essentially all plant-based foods cause significantly less eutrophying emissions than animal-based foods. Beef produces 58 times the eutrophication of tofu and 149 times that of corn.
Generally, animal-based foods produce 19 times the eutrophication of plant-based foods.
The Significance
Through many unique factors—bipedalism, large brains, cooking, agriculture, fossil fuel energy, etc.—we humans have been able to grow our populations to levels that couldn't otherwise be achieved. Much of the surface of the Earth and its resources now go towards producing food to feed us. +Livestock outweigh wild mammals by a factor of 15 to 1. Food production occurs on a massive scale and has major environmental impacts. Agriculture is now flirting with the limits of what Earth can provide.
Recognizing the impact of our diet can help us make better food decisions for the preservation of the systems that sustain our lives. Plant-based diets do indeed require far fewer resources than animal-based ones.
Eating less meat and dairy can have a significant impact. Americans get 33% of our calories from animal products. That puts us at a trophic level of around 2.33. If we cut that in half and drop our trophic level to 2.17 to match the world average of 17% of calories from animals, we could reduce the amount of land required to produce our food by 42% and save 31,000 gallons per year per person of our dwindling freshwater resources. And we'd cut our diet-related greenhouse gas emissions and eutrophying pollution by over 40%.
"That's great, but what about my health?" I, too, was convinced that a vegan diet was not healthy. For a couple of years now, I've been personally testing the health and fitness effects of different diets with comprehensive bloodwork, VO2 max tests, and Dexa scans. One of the consistent findings is that the less meat I eat, the healthier I am. It seems what's good for our health is good for the planet's too.
Of the many things you can personally do to help create a sustainable civilization and preserve the health of our threatened ecosystems, eating less meat may be the most significant. Resources generally have an economic cost. That means the lower resource intensity of plant-based foods makes them cheaper, too.
We have reached a point in human development where we can choose what we eat, and those choices have ripple effects on the environment. By understanding trophic levels and the flow of energy through ecosystems, we can make more informed decisions about our diets. Eating lower on the trophic pyramid—more plants and fewer animals—can significantly reduce the water, energy, and land we use and the pollution we create.
With every meal comes a choice and a responsibility. By reducing meat consumption and switching to plant-based foods, we can help build a more sustainable future for ourselves and the ecosystems that support us.
Author's note: This article is part 2. Part 1Â is about the physics of how energy flows through ecosystems and provides more context for the conclusions drawn here.
Question for you:
How will you change your diet, knowing the impact?
What else can be done to limit the environmental impacts of eating?
If you haven't checked out the food production page on Our World in Data, it's worth exploring.
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