By this yardstick, livestock now accounts for 18 percent of man-made carbon emissions, driven by the surge in demand for meat and dairy products, FAO said.

Global meat production is set to more than double from 229 million tonnes in 2001 to 465 million tonnes in 2050, according to a UN projection. Milk output is projected to soar from 580 million to 1,043 million tonnes over the same period.

"When emissions from land use and land use change are included, the livestock sector accounts for nine percent of CO2 deriving from human-related activities, but produces a much larger share of even more harmful greenhouse gases."

It generates 65 percent of human-caused nitrous oxide, a gas that is 296 times more effective at trapping solar heat than carbon dioxide (CO2), the biggest greenhouse-gas by volume. Most of this pollution comes from manure.

Livestock also accounts for 37 percent of all human-induced methane, which is 23 times as warming as CO2 and is largely produced by the digestive system of ruminants, and for 64 percent of ammonia, a big contributor to acid rain.

Not only that, but livestock's demand for feed crops contributes to biodiversity loss. The report proposes to increase the efficiency of livestock production and feed crop agriculture, and to improve animals' diets to reduce fermentation and consequent methane emissions.

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