Agriculture accounted for an estimated emission of 5.1 to 6.1 GtCO2-eq/yr in 2005 (10-12% of total global anthropogenic emissions of greenhouse gases (GHGs)). CH4 contributes 3.3 GtCO2-eq/yr and N2O 2.8 GtCO2-eq/yr. Of global anthropogenic emissions in 2005, agriculture accounts for about 60% of N2O and about 50% of CH4 (medium agreement, medium evidence). Despite large annual exchanges of CO2 between the atmosphere and agricultural lands, the net flux is estimated to be approximately balanced, with CO2 emissions around 0.04 GtCO2/yr only (emissions from electricity and fuel use are covered in the buildings and transport sector, respectively). Globally, agricultural CH4 and N2O emissions have increased by nearly 17% from 1990 to 2005, an average annual emission increase of about 60 MtCO2-eq/yr.
Future farming must contribute to the highest degree of sustainable resources management and to sufficient production and supply of high quality nutrients and energy. Carbon dioxide neutral systems will be a key issue for future farming since this will open the energy market for farmers and contribute to sustainability at the same time. Biofuels are sometimes described as green fuels. Most biofuels are made from crops. As the crops grow, they absorb carbon dioxide from the atmosphere. So the carbon dioxide that escapes when biofuels are burnt is subsequently absorbed by new plants growing to produce more biofuels – it’s a ‘virtuous’ circle.
Methane is the second most important greenhouse. Once emitted, methane remains in the atmosphere for approximately 9-15 years an is about 21 times more effective in trapping heat in the atmosphere than carbon dioxide over a 100-year period. In fact, according to a report published by the United Nations Food and Agriculture Organization, the livestock sector generates more greenhouse gas emissions as measured in CO2 equivalent – 18 percent, expected to double by 2050 according to IPCC – than transport. Says Henning Steinfeld, Chief of FAO’s Livestock Information and Policy Branch and senior author of the report: “Livestock are one of the most significant contributors to today’s most serious environmental problems. Urgent action is required to remedy the situation.”
The harmful environmental effects of livestock production are becoming increasingly serious at all levels—local, regional, national and global—and urgently need to be addressed, according to researchers from Stanford University, the United Nations Food and Agriculture Organization (FAO) and other organizations.
Globally, livestock are the most important source of anthropogenic methane emissions. Among domesticated livestock, ruminant animals produce significant amounts of methane as part of their normal digestive processes. In the rumen of these animals, microbial fermentation converts fibrous feed into products that can be digested and utilized by the animal. The microbial fermentation process, referred to as enteric fermentation, produces methane as a by-product, which is exhaled by the animal. And it accounts for respectively 37 percent of all human-induced methane, around 900 billion tonnes every year, and 64 percent of ammonia, which contributes significantly to acid rain.