Query: Burning fuel to produce fertiliser to grow feed, to  produce meat and to transport it - and clearing vegetation for grazing -  produces 9 per cent of all emissions of carbon dioxide, the most common  greenhouse gas.

Relevant passages:
Carbon dioxide <=SEP=> Carbon dioxide ( chemical formula ) is a colorless gas with a density about 60 % higher than that of air ( 1.225 g/L ) that is odorless at normally encountered concentrations . Carbon dioxide consists of a carbon atom covalently double bonded to two oxygen atoms . It occurs naturally in Earth 's atmosphere as a trace gas at a concentration of about 0.04 percent ( 400 ppm ) by volume . Natural sources include volcanoes , hot springs and geysers , and it is freed from carbonate rocks by dissolution in water and acids . Because carbon dioxide is soluble in water , it occurs naturally in groundwater , rivers and lakes , ice caps , glaciers and seawater . It is present in deposits of petroleum and natural gas .   As the source of available carbon in the carbon cycle , atmospheric carbon dioxide is the primary carbon source for life on Earth and its concentration in Earth 's pre-industrial atmosphere since late in the Precambrian has been regulated by photosynthetic organisms and geological phenomena . Plants , algae and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water , with oxygen produced as a waste product .   Carbon dioxide is produced by all aerobic organisms when they metabolize carbohydrates and lipids to produce energy by respiration . It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals , including humans . Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread , beer and winemaking . It is produced by combustion of wood and other organic materials and fossil fuels such as coal , peat , petroleum and natural gas .   It is a versatile industrial material , used , for example , as an inert gas in welding and fire extinguishers , as a pressurizing gas in air guns and oil recovery , as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying . It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence . The frozen solid form of , known as `` dry ice '' is used as a refrigerant and as an abrasive in dry-ice blasting .   Carbon dioxide is the most significant long-lived greenhouse gas in Earth 's atmosphere . Since the Industrial Revolution anthropogenic emissions - primarily from use of fossil fuels and deforestation - have rapidly increased its concentration in the atmosphere , leading to global warming . Carbon dioxide also causes ocean acidification because it dissolves in water to form carbonic acid .

Agriculture <=SEP=> Agriculture or farming is the cultivation and breeding of animals , plants and fungi for food , fiber , biofuel , medicinal plants and other products used to sustain and enhance human life . Agriculture was the key development in the rise of sedentary human civilization , whereby farming of domesticated species created food surpluses that nurtured the development of civilization . The study of agriculture is known as agricultural science . The history of agriculture dates back thousands of years , and its development has been driven and defined by greatly different climates , cultures , and technologies . Industrial agriculture based on large-scale monoculture farming has become the dominant agricultural methodology .   Modern agronomy , plant breeding , agrochemicals such as pesticides and fertilizers , and technological developments have in many cases sharply increased yields from cultivation , but at the same time have caused widespread ecological damage and negative human health effects . Selective breeding and modern practices in animal husbandry have similarly increased the output of meat , but have raised concerns about animal welfare and the health effects of the antibiotics , growth hormones , and other chemicals commonly used in industrial meat production . Genetically modified organisms are an increasing component of agriculture , although they are banned in several countries . Agricultural food production and water management are increasingly becoming global issues that are fostering debate on a number of fronts . Significant degradation of land and water resources , including the depletion of aquifers , has been observed in recent decades , and the effects of global warming on agriculture and of agriculture on global warming are still not fully understood .   The major agricultural products can be broadly grouped into foods , fibers , fuels , and raw materials . Specific foods include cereals ( grains ) , vegetables , fruits , oils , meats and spices . Fibers include cotton , wool , hemp , silk and flax . Raw materials include lumber and bamboo . Other useful materials are also produced by plants , such as resins , dyes , drugs , perfumes , biofuels and ornamental products such as cut flowers and nursery plants . Over one third of the world 's workers are employed in agriculture , second only to the service sector , although the percentages of agricultural workers in developed countries has decreased significantly over the past several centuries .

Greenhouse gas <=SEP=> A greenhouse gas ( abbrev . GHG ) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range . This process is the fundamental cause of the greenhouse effect . The primary greenhouse gases in Earth 's atmosphere are water vapor , carbon dioxide , methane , nitrous oxide , and ozone . Without greenhouse gases , the average temperature of Earth 's surface would be about -18 ° C , rather than the present average of 15 ° C . In the Solar System , the atmospheres of Venus , Mars and Titan also contain gases that cause a greenhouse effect .   Human activities since the beginning of the Industrial Revolution ( taken as the year 1750 ) have produced a 40 % increase in the atmospheric concentration of carbon dioxide , from 280 ppm in 1750 to 406 ppm in early 2017 . This increase has occurred despite the uptake of a large portion of the emissions by various natural `` sinks '' involved in the carbon cycle . Anthropogenic carbon dioxide emissions ( i.e. , emissions produced by human activities ) come from combustion of fossil fuels , principally coal , oil , and natural gas , along with deforestation , soil erosion and animal agriculture .   It has been estimated that if greenhouse gas emissions continue at the present rate , Earth 's surface temperature could exceed historical values as early as 2047 , with potentially harmful effects on ecosystems , biodiversity and the livelihoods of people worldwide . Recent estimates suggest that on the current emissions trajectory the Earth could pass a threshold of 2 ° C global warming , which the United Nations ' IPCC designated as the upper limit to avoid `` dangerous '' global warming , by 2036 .