The UN body also cautioned that existing levels could increase by as much as 30% by 2050 without greater efforts to reduce them.
This is the first time that FAO has released its own global estimates of greenhouse gas emissions from agriculture as part of the latest assessment report of the Intergovernmental Panel on Climate Change (IPCC).
Agricultural emissionsfrom crop and livestock production grew from 4.7bn tonnes of carbon dioxide equivalents in 2001 to over 5.3bn tonnes in 2011, a 14% increase. The increase occurred mainly in developing countries, due to an expansion of total agricultural outputs.
Meanwhile, net greenhouse gas emissions due to land use change and deforestation registered a close to 10% decrease over the 2001-2010 period, averaging some 3bn tonnes of CO2 equivalent per year over the decade. This was the result of reduced levels of deforestation and increases in the amount of atmospheric carbon being sequestered in many countries.
China and India lead the way by quite a distance globally as the top greenhouse gas producers from agriculture.
Sources of agricultural emissions
The largest source of greenhouse emissions within agriculture is enteric fermentation - when methane is produced by livestock during digestion and released via belches - this accounted in 2011 for 39% of the sector's total greenhouse gas outputs. Emissions from enteric fermentation increased 11% between 2001 and 2011.
Emissions generated during the application of synthetic fertilisers accounted for 14% of agricultural emissions in 2011, and is the fastest growing emissions source in agriculture, having increased some 37% since 2001.
Greenhouse gases resulting from biological processes in rice paddies that generate methane make up 10% of total agricultural emissions.
In 2011, 45% of agriculture-related greenhouse outputs occurred in Asia, followed by the Americas (25%), Africa (15%), Europe (11%), and Oceania (4%), according to FAO's data. This regional distribution was fairly constant over the last decade. In 1990, however, Asia's contribution to the global total (38%) was smaller than at present, while Europe's was much larger at 21%.
Figures for energy use
The new FAO data also provides a view of emissions from energy use in the agriculture sector generated from traditional fuel sources, including electricity and fossil fuels burned to power agricultural machinery, irrigation pumps and fishing vessels.
These emissions exceeded 785m tonnes of CO2 equivalents in 2010, having increased by 75% since 1990.
"FAO's new data represent the most comprehensive source of information on agriculture's contribution to global warming made to date," said Francesco Tubiello of the organisation's Climate, Energy and Tenure Division.
"Up to now, information gaps have made it extremely difficult for scientists and policymakers to make strategic decisions regarding how to respond to climate change and has hampered efforts to mitigate agriculture's emissions.”