Veganism

A vegan is a vegetarian who does not eat any animal products or by-products, including eggs, dairy, honey, and any meat or seafood. A vegan usually does not use animal products such as leather or wool either.

Impact on resource use and climate change
The production of animal products, not only meat, but also eggs and milk, needs much more energy than food from plants. Estimations are a factor between 7 and 10.

Because the methane they belch is 23 times more effective at trapping heat than, livestock causes more global warming than all the human transportation systems combined. 

Impact on Human Health
Animal products are implicated in all kinds of human health problems. The obvious ones are things like obesity (meat and dairy are more calorie-dense than vegetative matter), and heart and artery disease (no cholesterol in plants). But the largest study of the connection between health and diet ever conducted (The China Study) concludes that animal protein is a carcinogen, and is implicated in everything from diabetes to lupus.

Resources and the environment


People who adopt veganism for environmental reasons often do so because it consumes fewer resources and causes less environmental damage. Organizations such as PETA point out that animal agriculture is linked to climate change, water pollution, land degradation, a decline in biodiversity, and that a commercially available animal-based diet uses more land, water, and energy than a strictly vegetarian one.

The United Nations Food and Agriculture Organization released a report in November 2006 linking animal agriculture to environmental damage. The report, Livestock's Long Shadow, concluded that the livestock sector (primarily cows, chickens, and pigs) was one of the two or three most significant contributors to the planet's most serious environmental problems, at every scale from local to global. According to the report, it is responsible for at least 18 percent of the world's greenhouse gas emissions, as measured in CO2 equivalents. Livestock sources (including enteric fermentation and manure) account for about 3.1 percent of US anthropogenic GHG emissions expressed as carbon dioxide equivalents. This EPA estimate is based on methodologies agreed to by the Conference of Parties of the UNFCCC, with 100-year global warming potentials from the IPCC Second Assessment Report used in estimating GHG emissions as carbon dioxide equivalents. In June 2010, a report from United Nations Environment Programme declared that a global shift towards a vegan diet was needed to save the world from hunger, fuel shortages and climate change.

Greenhouse gas emissions are not limited to animal husbandry. Plant-based sources such as rice cultivation cause similar problems. A 2007 study that simulated the land use for various diets for the geography of New York State concluded that, although vegetarian diets used the smallest amount of land per capita, a low-fat diet that included some meat and dairy—less than 2 oz of meat/eggs per day – significantly less than that consumed by the average American – could support slightly more people on the same available land than could be fed on some high-fat vegetarian diets, since animal food crops are grown on lower-quality land than are crops for human consumption.

Debate over animals killed in crop harvesting


Steven Davis, a professor of animal science at Oregon State University, argued in 2001 that the least-harm principle does not require giving up all meat, because a plant-based diet would not kill fewer animals than one containing beef from grass-fed ruminants. Davis wrote that cultivating crops also kills animals, because when a tractor traverses a field, animals are accidentally destroyed. Based on a study finding that wood mouse populations dropped from 25 per hectare to five per hectare after harvest (attributed to migration and mortality), Davis estimated that 10 animals per hectare are killed from crop farming every year. If all 120000000 acre of cropland in the continental United States were used for a vegan diet, then approximately 500 million animals would die each year. But, if half the cropland were converted to ruminant pastureland, he estimated that only 900,000 animals would die each year—assuming people switched from the eight billion poultry killed each year to beef, lamb, and dairy products.

if one acre of cropland in the continental United States were used for a vegan diet, then approximately 25/6 animals would die each year

if one square kilometer of cropland in the continental United States were used for a vegan diet, then approximately 50,000/49 animals would die each year

Davis's analysis was criticized in 2003 by Gaverick Matheny and Andy Lamey in the Journal of Agricultural and Environmental Ethics. Matheny argued that Davis had miscalculated the number of animal deaths based on land area rather than per consumer, and incorrectly equated "the harm done to animals ... to the number of animals killed." Matheny argued that per-consumer, a vegan diet would kill fewer wild animals than a diet adhering to Davis's model, and that vegetarianism "likely allows a greater number of animals with lives worth living to exist." Lamey argued that Davis's calculation of harvesting-related deaths was flawed because based on two studies; one included deaths from predation, which is "morally unobjectionable" for Regan, and the other examined production of a nonstandard crop, which Lamey argued has little relevance to deaths associated with typical crop production. Lamey also argued, like Matheny, that accidental deaths are ethically distinct from intentional ones, and that if Davis includes accidental animal deaths in the moral cost of veganism, he must also evaluate [claimed] increased human deaths associated with his proposed diet, which Lamey argued leaves "Davis, rather than Regan, with the less plausible argument."