Dear V.,

I get, basically, the health and ethical reasons we’re told not to eat meat. But at least chickens and cows don’t have to be sprayed with fertilizers and pesticides. Are there any real environmental reasons not to eat meat?

— Chris (New Hampshire)

Dear Chris,

Yes! The environmental impacts of eating meat on an over-crowded planet are very real, and very profound. I hate to have to tell you, but meat production uses more fertilizers and pesticides than any other industry (sprayed directly on the animals, and on the crops that feed them). Here’s an overview of just some of the other repercussions:

Meat production is "one of the top two or three most significant contributors to the most serious environmental problems, at every scale from local to global" according to the United Nations report, Livestock’s Long Shadow. The report, like many other studies, identifies an array of environmental consequences of animal agriculture: land degradation, climate change, air and water pollution, water shortages, deforestation and loss of biodiversity.

Climate change: Meat production accounts for about 20 percent of greenhouse gas emissions, more than the emissions from planes, trains, cars and boats combined. These emissions are largely in the form of CO2 — the main source of global warming — and from some of the lesser-known greenhouse gases.

About 65 percent of our nitrous oxide emissions — which is 296 times more potent than CO2 — are generated by animal agriculture. The Environmental Protection Agency, or EPA, says animal agriculture is the number one source of methane emissions in the U.S. Like nitrous oxide, methane has greater global warming potential than CO2, in this case 23 times more. Researchers at the University of Chicago found that the average American diet produces 1.5 tons more greenhouse gases than a no-meat diet.

Meat production serves up a double whammy in terms of global warming: Not only does it produce one-fifth of our greenhouse gas emissions, meat production also devours the plants and stable land that would otherwise absorb CO2.

Water shortages: An astounding amount of water — more than it takes to grow all our fruits and vegetables — is used to raise meat. It is estimated that worldwide, half of all fresh water is used for livestock. Keep in mind that 2.6 billion people lack access to drinking water, and 1,000 children die every day for lack of it.

In 2000, annual consumption of meat in the U.S. was 180 pounds per person, including 65 pounds of beef (the numbers have increased since then, and continue to rise). The water necessary to produce one pound of steak is equal to the annual water consumption of an average household. So the average American is using the equivalent of 65 households’ worth of water by their beef consumption alone.

Water pollution: Most of the water not consumed by animal agriculture is polluted by animal agriculture. Even the EPA recognizes that animal waste pollutes our waterways more than all other industrial sources combined.

As I mentioned, vast amounts of petrochemicals, pesticides and chemical fertilizers are used in meat production. Enter the term "dead zones." These are huge, oxygen-depleted areas of ocean that can no longer support aquatic life. Growing feed for land-based meat is effectively destroying water-based meat. As Richard Manning pointed out in 2004, “the dead zone has seriously damaged what was once a productive fishery, meaning that a high-quality source of low-cost protein is being sacrificed so that a source of low-quality, high-input subsidized protein can blanket the Upper Midwest.” He was referring to the Dead Zone — now the size of New Jersey — at the mouth of the Mississippi, caused by fertilizer run-off from Midwest farms.

Add to the fertilizers and other toxins the astounding amount of animal waste generated by factory farms and it comes as no surprise that animal production is the primary source of damage to coastal waters in North and South America, Europe and Asia, with more than 60 percent of coastal waters in the U.S. “moderately” to “severely” polluted by factory farms.

Land degradation: Meat in our diets takes its toll on Earth’s surface in two main ways: over-grazing and use of land to grow feed for animals. As demand for animal products rise, demand on the lands that support grazing or feed production becomes overwhelming (that is, unsustainable).

Lester Brown, my personal hero and founder of the Worldwatch Institute, calculated that the needs of 230 million cattle, 246 million sheep and 175 million goats grazing on the African continent exceed the lands’ capacity by at least half. In 2000, feed demand for India’s cattle herd — the world’s largest — was an estimated 700 million tons, but the sustainable supply was 540 million tons.

Clearing land to graze animals or to grow animal feed leads to erosion, food shortages (as land to grow other crops is reduced, and eventually left barren), and global warming (from loss of plant life that would otherwise absorb CO2). ''Overgrazing of rangelands,” notes Brown, “initially reduces their productivity but eventually it destroys them, leaving desert.” Enter the term "desertification": the process whereby fertile and stable lands become — you got it — deserts. We lose billions of tons of topsoil every year to rising demands for meat and irresponsible growing and grazing practices — a rate that, putting it lightly, far outpaces the 100 to 500 years it takes to produce one inch of topsoil. (Industrial farming loses up to six inches of topsoil a year.)

Deforestation and biodiversity: Globally, we are using more and more land to make room for more and more animals and the crops needed to feed them. An estimated 30 percent of the earth’s ice-free land is involved in livestock production, according to the U.N.’s Food and Agriculture Organization. Forests are a precious means of removing CO2 from the atmosphere, supporting biodiversity and maintaining soil health and climate stability, but rain forests (Brazil) and ancient pine forests (China) — entire ecosystems worldwide — are being destroyed to feed the animals that feed us. The expanding use of land for grazing and growing animal feed crops is now a dominant reason for deforestation in most countries. Deforestation contributes to global warming, topsoil depletion, drought, plant and animal extinction, and loss of biodiversity. Basically, we are devouring trees to make way for an ever-increasing number of farmed animals. These animals, in turn, devour vast amounts of energy, natural resources and food calories, so that we can, in turn, devour their meat.

To give you some sense of the vast tracts of land needed to graze or otherwise feed the animals that feed us, scientists at the Smithsonian Institute figure that the equivalent of seven football fields of land is bulldozed every minute. Every minute. According to the U.S. General Accounting Office, more plant species are threatened or annihilated by livestock grazing than by any other cause.

We’ve just covered six of the most significant environmental consequences of feeding our desire for animal products. There are at least three more I want to recount in order to answer your question: dangers to human health, food shortages and impacts of confined animal feeding operations, or CAFOs. So tune in next week for part two of my answer.

Stay Green (and eat mostly greens),