Human impact on nature Plan: Human impact on nature

Meat production[edit]
Main article: Environmental impact of meat production
Worldwide, the animal industry provides only 18% of calories, but uses 83% of agricultural land and emits 58% of food's greenhouse gas emissions.^[77]
Biomass of mammals on Earth^[78]
  Livestock, mostly cattle and pigs (60%)
  Humans (36%)
  Wild mammals (4%)
A village palm oil press "malaxeur" in Bandundu, Democratic Republic of the Congo
Environmental impacts associated with meat production include use of fossil energy, water and land resources, greenhouse gas emissions, and in some instances, rainforest clearing, water pollution and species endangerment, among other adverse effects.^[79][80] Steinfeld et al. of the FAO estimated that 18% of global anthropogenic GHG (greenhouse gas) emissions (estimated as 100-year carbon dioxide equivalents) are associated in some way with livestock production.^[79] FAO data indicate that meat accounted for 26% of global livestock product tonnage in 2011.^[81]
Globally, enteric fermentation (mostly in ruminant livestock) accounts for about 27% of anthropogenic methane emissions,^[82] Despite methane's 100-year global warming potential, recently estimated at 28 without and 34 with climate-carbon feedbacks,^[82] methane emission is currently contributing relatively little to global warming. Although reduction of methane emissions would have a rapid effect on warming, the expected effect would be small.^[83] Other anthropogenic GHG emissions associated with livestock production include carbon dioxide from fossil fuel consumption (mostly for production, harvesting and transport of feed), and nitrous oxide emissions associated with the use of nitrogenous fertilizers, growing of nitrogen-fixing legume vegetation and manure management. Management practices that can mitigate GHG emissions from production of livestock and feed have been identified.^{[84][85][86][87][88]}
Considerable water use is associated with meat production, mostly because of water used in production of vegetation that provides feed. There are several published estimates of water use associated with livestock and meat production, but the amount of water use assignable to such production is seldom estimated. For example, "green water" use is evapotranspirational use of soil water that has been provided directly by precipitation; and "green water" has been estimated to account for 94% of global beef cattle production's "water footprint",^[89] and on rangeland, as much as 99.5% of the water use associated with beef production is "green water".
Impairment of water quality by manure and other substances in runoff and infiltrating water is a concern, especially where intensive livestock production is carried out. In the US, in a comparison of 32 industries, the livestock industry was found to have a relatively good record of compliance with environmental regulations pursuant to the Clean Water Act and Clean Air Act,^[90] but pollution issues from large livestock operations can sometimes be serious where violations occur. Various measures have been suggested by the US Environmental Protection Agency, among others, which can help reduce livestock damage to streamwater quality and riparian environments.^[91]
Changes in livestock production practices influence the environmental impact of meat production, as illustrated by some beef data. In the US beef production system, practices prevailing in 2007 are estimated to have involved 8.6% less fossil fuel use, 16% less greenhouse gas emissions (estimated as 100-year carbon dioxide equivalents), 12% less withdrawn water use and 33% less land use, per unit mass of beef produced, than in 1977.^[92] From 1980 to 2012 in the US, while population increased by 38%, the small ruminant inventory decreased by 42%, the cattle-and-calves inventory decreased by 17%, and methane emissions from livestock decreased by 18%;^[70] yet despite the reduction in cattle numbers, US beef production increased over that period.^[93]
Some impacts of meat-producing livestock may be considered environmentally beneficial. These include waste reduction by conversion of human-inedible crop residues to food, use of livestock as an alternative to herbicides for control of invasive and noxious weeds and other vegetation management,^[94] use of animal manure as fertilizer as a substitute for those synthetic fertilizers that require considerable fossil fuel use for manufacture, grazing use for wildlife habitat enhancement,^[95] and carbon sequestration in response to grazing practices,^[96][97] among others. Conversely, according to some studies appearing in peer-reviewed journals, the growing demand for meat is contributing to significant biodiversity loss as it is a significant driver of deforestation and habitat destruction.^{[98][99][100][33]} Moreover, the 2019 Global Assessment Report on Biodiversity and Ecosystem Services by IPBES also warns that ever increasing land use for meat production plays a significant role in biodiversity loss.^[101][102] A 2006 Food and Agriculture Organization report, Livestock's Long Shadow, found that around 26% of the planet's terrestrial surface is devoted to livestock grazing.^[103]