SANE AND SELFISH REASONS TO NOT EAT PIECES OF ANIMALS.
1. IT IS ENERGY WISEMeat production requires 10 to 20 times more energy per edible tonne than grain production and has as high as a 54:1 protein inefficiency ratio (54 units of plant protein are required to produce a single unit of meat protein) . Each cow raised requires (directly and indirectly) 90 to 180 litres of water a day and passes 40kg of manure per kg of edible animal tissue. A study by the National Institute of Livestock and Grassland Science in Japan estimated that 1kg (2.2 pounds) of beef is responsible for the equivalent amount of carbon dioxide emitted by the average European car every 250 kilometers, and burns enough energy to light a 100-watt bulb for nearly 20 days .
Protein rich beans require only fertilization, water and land, with very little maintenance.
Once grown, there's a long list of energy expensive processes required to turn animals into legally consumable food; from transporting them to the abottoir, slaughtering them, cutting them into pieces, sanitizing and packaging the pieces (usually in plastic) and then delivering the result to shops where they are refrigerated until sale. Refrigeration alone is extremely energy expensive. Suffice to say very few people would be able to eat animals today were it not for this sprawling, around-the-clock, energy infrastructure.
The process required to turn beans, grains and nuts into pantry-apt food is minimal and has an extremely long shelf life, no need for energy expensive refrigeration.
2. GOT KIDS? IT IS AN ENVIRONMENTAL INVESTMENT IN THEIR FUTURE'Livestock production' uses more than 30% of the earth's entire land surface, with beef ranches driving 60-70% of Amazon deforestation today[5a][5b]. Conservative forecasts assume that over half of all arable land on earth will be dedicated to the production of cow parts, cow milk, chicken and pig parts by 2050.
Soya has 4 times more calories than red meat so the amount of soy that could be grown using the same amount of land would feed far more people than if used to raise cows. More so, a animal-tissue-based diet requires 7 times more land on average than a plant-based diet yet (somewhat ironically) much of the meat eaten world-wide is raised on soya grain. 98% of all soy grown in America, for instance, is fed to livestock rather than people directly. This makes American meat eaters the primary drivers of soy bean monocrops in that country . The trick here is to eat the bean before it gets to the cow. The more cows, pigs and chicken eaten, the more competition there is for wooded land. The more demand for animal parts, the more monocrops there are, significantly threatening the biodiversity upon which we all depend.
Agriculture has negative secondary effects. The Earth is increasingly saturated in animal waste, far more than it can readily process. Animal waste from agriculture accounts for 50-85% of all ammonia found on land and in water, contributing significantly to acid rain and air pollution worldwide .
According to The United Nations Food & Agriculture Organization, livestock production is at the heart of almost every environmental stress confronting the planet: rain forest destruction, growing deserts, loss of fresh water, air and water pollution, acid rain, floods and soil erosion. 
3. FISH EATING IS DESTROYING OCEAN LIFEHard to believe, given that we were all told the ocean is apparently abundant and endless, but it's true: 40% of the worlds oceans are considered by experts to be detrimentally affected by fishing. According to an FAO estimate, over 70% of the world's fish species are either exploited to unsustainable limits or depleted.
Species such as the Blue Fin Tuna are now endangered alongside 69 other species of fish in abundance just decades ago . It is safe to say much of the fish eaten by children today may be extinct by the time they are adults.
The global harvest for fish has more than quadrupled since 1950, from 22 million tonnes to 100 million tonnes over the same period. The environmental cost is already unimaginable, along with a real threat for consumers' health from the unnatural conditions of inland fish farms. A detailed account of both kinds of production can be found here and here.
If you like the ocean it's a good idea to stop funding the industries that harm it. It appears too late to hope for regulation, let alone waiting hundreds of years for coral reefs and underwater ecosystems to heal. You can help slow the decay by choosing not to buy fish. If you are a person that believes it's not possible to live without fish, catch it yourself with a hook and rod; this has significantly lower environmental impact than any other modern means of catching fish.
4. QUITTING ANIMAL TISSUE IS GOOD FOR YOU AND OTHER PEOPLEMeat eaters generally consume more than twice as much protein as they need, increasing likelihood of kidney failure, cholesterol, heart failure, hypertension, diabetes, stress. 
Legumes, especially soybeans, contain the largest percentage of protein among the vegetable foods and are in the same range as many meats. If legumes are a central part of a person's diet, there will be plenty of enough protein in the diet with no need for animal-tissue. For example, one cup of cooked soybeans contains approximately 20 grams of protein; that is equivalent to three hot dogs, a quarter-pound hamburger, three 8-ounce cups of milk, three ounces of cheese.
On the other hand, industrially produced meat and fish is famously full of nasty things, from bleaching agents to antibiotics, responsible for allergies, resistance to medicines, fatigue, dehydration and a long list of cancers. See here and here.
Cows consume 80% of all antibiotics produced in America [10a][10b][10c] and at least 45% in the European Union in order to combat the illnesses they get when fed grains (cows and pigs didn't evolve to eat corn and beans) and those from intensive farming.
Antiobiotics fed to animals are almost always in the same medical group as that of those fed to humans, and so when bacteria develops a resistance to antiobiotics on a farm it cannot be fought when encountered in people. This is the history of most epidemcis (like E-Coli) threatening modern human life.
Many scientists consider antibiotic-resistant bacteria to be the greatest threat to humans on the planet today. Grass-fed, 'organic' animal parts are no guarantee of safety either due to it so very often coming into contact with industrially produced animal parts.[10b]
Antiobiotics from animal parts also end up in the bodies of those that consume them, alongside doses of hormones known to have significantly detrimental impact on people, especially children . The hormone Oestradiol 17ß, used widely by major exporters of cow pieces, is considered a complete carcinogen. It exerts both tumour initiating and tumour promoting effects.
The eating of meat affects other people, contributing significantly to food shortages worldwide. In the U.S., animals are fed more than 80 percent of the corn and 95 percent of the oats grown. The world's cattle alone consume a quantity of food once estimated (Gold and Porrit) to be equal to the caloric needs of 8.7 billion people, more than the entire human population on Earth. Instead, a vast proportion of the world's forests have been felled to grow the grains fed to cattle. A report from the United Nations Framework Convention on Climate Change considers agriculture to be the single most prevalent cause of deforestation throughout human history , depleting world oxygen supply, threatening and/or extinguishing animal and insect life, tipping surrounding ecosystems and devastating indigenous communities and their cultures.
Consider also the impact on supplies of freshwater. To produce 1kg of feedlot beef requires 7kg of feed grain, which takes around 7000 litres of water throughput to grow. The demand for water to grow food to feed cows is resulting in vast areas of arid, dying land throughout the world as water is pumped out to feedlot farms elsewhere. Reference adapted to metric, from here.
While the increasing demand for 'organic' meat in 1st world countries has a less negative impact on the soil itself, cows still require water and cleared land on which to graze. More so, as organic meat cannot be grown as quickly as hormone engineered meat these animals consume more land and require a larger amount of plant matter over the course of a lifetime.
The Agriculture industry is full of many clever and well researched people, all looking to profit where possible: there would be more grass fed cows if it was as or more efficient than industrial methods. Replacing industrialised meat with grass-fed alternatives would rely on vastly greater rates of deforestation than currently experienced while prohibitively raising the cost of animal parts themselves (see Author's note, below). 'Organic meat' is thus not a drop-in solution at the current rates of meat consumption. It is safe to say meat is no longer an environmentally or socially responsible source of protein at today's population levels. It was 'sustainable' once, but not at all now.
If you are a person that believes it's not possible to live without eating meat you may consider exploring a more immediate relationship with your choice of diet, with the origin of what you choose to put into your body. Rather than paying someone to kill on your behalf, find a local farmer and arrange to learn to kill the animal you select for eating, preparing the parts for transportation once done; the parts you freeze will last you a very long time.
Julian, one of the authors of this document, grew up on a small farm and attests to the awakening importance of learning to do this, a perspective those that wish to sell you animal parts (and the large agricultural corporations they work for) would rather you do not have.
A LIST OF INTERESTING CITATIONS TO RUMINATE UPONMost of us are aware that our cars, our coal-generated electric power and even our cement factories adversely affect the environment. Until recently, however, the foods we eat had gotten a pass in the discussion. Yet according to a 2006 report by the United Nations Food and Agriculture Organization (FAO), our diets and, specifically, the meat in them cause more greenhouse gases carbon dioxide (CO2), methane, nitrous oxide, and the like to spew into the atmosphere than either transportation or industry. 
Approximately 10 billion animals a year are killed in the USA so that some parts of them can be eaten by people. 
According to a 2006 report by the Livestock, Environment And Development Initiative, the livestock industry is one of the largest contributors to environmental degradation worldwide, and modern practices of raising animals for food contributes on a "massive scale" to air and water pollution, land degradation, climate change, and loss of biodiversity. The initiative concluded that "the livestock sector emerges as one of the top two or three most significant contributors to the most serious environmental problems, at every scale from local to global." In 2006 FAO estimated that meat industry contributes 18% of all emissions of greenhouse gasses. This figure was revised in 2009 by two World Bank scientists and estimated at 51% minimum.
Though some 800 million people on the planet now suffer from hunger or malnutrition, the majority of corn and soy grown in the world feeds cattle, pigs and chickens. This despite the inherent inefficiencies: about two to five times more grain is required to produce the same amount of calories through livestock as through direct grain consumption, according to Rosamond Naylor, an associate professor of economics at Stanford University. It is as much as 10 times more in the case of grain-fed beef in the United States. 
98% of all Soy grown in the United States is fed to livestock rather than people directly. 
"People who are comfortable eating meat, should be equally comfortable killing animals" - The Meat License proposal.
Food and Agriculture Organization of the United Nations report summary:
REFERENCES1. How meat contributes to Global Warming. Scientific American, 2009
2. Williams, Erin E. and DeMello, Margo. Why Animals Matter. Prometheus Books, 2007, p. 73.
3. The Environmental impact of Meat Production, Wikipedia page
4. New York Times analysis.
5. Livestock's Long Shadow, UN Food and Agricultural Organisation, 2006.
5a.Deforestation in the Amazon
6. U.S. could feed 800 million people with grain that livestockNews.cornell.edu. 1997-08-07. Retrieved 2010-05-01.
7. Overfishing: a threat to marine biodiversity
8. Guardian report on Compass ban of fish in restaurants
9. Meat and Health, UN Food and Agricultural Organisation.
10a. Farm Animals Get 80 Percent of Antibiotics Sold in U.S.
10b. Politics of the Plate: Drug Bust, Barry Estabrook, 2009
10c. Whether you buy grass-fed or 'natural' meat safety isn't guaranteed
11. Meat hygiene 10th edition, Von J. F. Gracey, D. S. Collins, Robert J. Huey, Harcourt Brace and Company, 1999.
12. Barnard ND, Nicholson A, Howard JL. The medical costs attributable to meat consumption. Prev Med. 1995;24:646-655.
13. UNFCCC (2007). "Investment and financial flows to address climate change". unfccc.int. UNFCCC. p. 81.
14. Encyclopedia Britannica entry for 'Soybean'.
15. Ammonia Emissions and Animal Agriculture, Virginia Tech.
N/A. A favourite meat-free recipes blog. Here's another and another.
This page was written by Marta Peirano and Julian Oliver.