Agriculture as a source of emissions

Emerging scientific evidence on temperature thresholds has injected greater urgency into discussions about how to avoid the consequence of dangerous climate change (IPCC, 2007). This agenda has been supported by The Stern Review of the Economics of Climate Change (Stern, 2006), which provides a compelling if contested economic basis for advancing greater spending on mitigation strategies. In most OECD countries there is now a proactive programme to determine where emissions reductions should take place.

Agriculture is a major source of global greenhouse emissions, accounting for an estimated emission of 5.1 to 6.1 Gt CO2-eq/yr in 2005. This represents 10-12% of total global anthropogenic emissions of greenhouse gases (GHGs) (Smith et al., 2007), although scientific uncertainly also suggests this could be as high as 18-31%. Methane (CH4), mainly from enteric fermentation, rice cultivation and manure handling, contributes 3.3 Gt CO2-eq/yr,: nitrous oxide (N2O), from a range of soil and land management practices, contributes 2.8 Gt CO2-eq/yr. Of global anthropogenic emissions agriculture is estimated to account for about 60% of N2O and about 50% of CH4. 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 Gt CO2/yr only (emissions from electricity and fuel-use are covered in the buildings and transport sector, respectively).

Agriculture and land-use also have large potential to act as sinks of carbon. Forests hold an enormous amount of carbon; however, significant volumes are also stored in soils and peatland. Changes in land-use and tillage practices can result in this carbon being released to the atmosphere.

1 Methane and nitrous oxide can be converted to carbon dioxide equivalents (CO2-eq) by multiplying by their global warming potentials of 21 and 310, respectively.

In addition, climate change itself may lead to the degradation of these resources and their subsequent release of carbon (Pielke et al., 2002) so it is vital to understand the role of land-use (including agriculture, horticulture and forestry) as both an emissions source and sink, and how this could change over time and with increasing levels of climate change.

Globally, agricultural CH4 and N2O emissions have increased by nearly 17% from 1990 to 2005, an average annual emission increase of about 60 Mt CO2-eq/yr. During that period, the five regions composed of NonAnnex I countries showed a 32% increase, and were, by 2005, responsible for about three quarters of total agricultural emissions. The other five regions, mostly Annex I countries, collectively showed a decrease of 12% in the emissions of these gases. OECD (2008) provides a breakdown for member states since 1990.

Without abatement measures, emissions are likely to climb steadily by 1.1% per year, from 6.2 Gt of CO2 equivalent, to 8.2 Gt CO2e in 2030 -equal to a 31% increase in emissions over the period, according to McKinsey & Company (2009). The increase is driven mainly by population growth and greater world demand for meat, linked to increased per capita GDP. These projections are, however, speculative, depending on demand-side changes (Fiala, 2008). Increasing concern about the magnitude of these emissions has been expressed in relation to the need to distribute mitigation between developing and developed countries (FAO, 2007). In some countries, estimated emissions have already fallen, largely due to falling livestock numbers and, in some regions, further spontaneous cuts are anticipated to deliver similar savings over the next decade or so. However, more aggressive emissions targets need to be developed with some consideration of the economic potential for mitigation within agriculture relative to other sectors. Current estimates suggest that this potential is approximately 1.5-1.6 Gt CO2e/year (by 2030), which is less than the total technical potential, of around 5.5-6 Gt CO2e/year (UNFCCC, 2008).

Ultimately there is a need to address agricultural emissions without compromising other objectives for the sector such as food security, environmental sustainability and poverty alleviation.

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