Annex 7.g Emissions from the agriculture sector

¶This annex describes emissions from agriculture now, historical and projected business as usual trends, drivers behind emissions growth, and prospects for emission cuts.

Now

¶Agriculture was responsible for 14% of global greenhouse gas (GHG) emissions in 2000¹¹ Data for 2000, sources: WRI (2006) and EPA (forthcoming).. Agriculture emissions are from the following sources, as shown in figure 1:

Fertilisers are the largest single source (38%) of emissions from agriculture. Agricultural soils release nitrous oxide (N2O) during the natural processes of nitrification and denitrification. Fertilisers (both man made and natural) increase the output of nitrous oxide from these processes.
Livestock is the second largest source of emissions, accounting for 31% of agriculture emissions. Methane (CH4) is produced as a waste product of digestion by ruminants, particularly cattle, and this process is known as enteric fermentation. Cattle, buffalo, sheep, goats and camels account for the majority of methane emissions produced.
Wetland rice cultivation emits 11% of agricultural emissions. The flooded rice fields mean that the organic matter cannot decompose in the presence of oxygen (i.e. anaerobic decomposition takes place) and methane is produced as a result. The level of emissions from rice cultivation is dependent upon the specific water management practices and quantity of organic matter involved.
Manure management methods, including the handling, storage and treatment of livestock waste, causes 7% of agricultural emissions. Methane is emitted when the manure is not stored in a sufficiently oxygenated environment, leading to anaerobic decomposition, while the nitrogen in livestock manure and urine encourages nitrification and denitrification, releasing nitrous oxide.
Burning of savannah and agricultural residues, and open burning from forest clearing contribute to other non-CO2 emissions from agriculture (accounting for 13% of emissions from the sector).

¶Figure 1 Sources of non-CO2 emissions from the agriculture sector (2000)²² Data source: EPA (forthcoming).

Agriculture is a producer of CO2 emissions via soil and biomass management practices that disturb the natural carbon sinks. This effect could be significant, but there are no robust global estimates of it. This effect is considered in annex 7.f: emissions from land use change and forestry sector.
The agriculture sector is also indirectly responsible for emissions in other sectors. Agriculture is a key driver for land use change such as deforestation, which generates emissions (as discussed in annex 7.f). Also, production of fertiliser, use of agricultural equipment that requires an energy source, and transportation of agricultural inputs and outputs leads to emissions from the industry, power, and transport sectors respectively. These effects are not included in the emission estimates quoted in this annex.

¶Developing countries account for the majority (almost three quarters) of agricultural emissions. In the case of rice, almost 90% of emissions currently come from China and South East Asia. Much of agricultural output is traded, such that agricultural output accounted for 9% of the value of all world trade in 2003 (totalling $674bn)³³ WRI (2005).. Therefore, if the environmental footprint of agriculture emissions was calculated according to consumption, the developed / developing country split would look quite different.

Historic and Business as Usual Projected Trends

¶Agriculture emissions increased 10% between 1990 and 2000, most of which came from increased emissions from other agricultural sources (such as burning agricultural residues)⁴⁴ EPA (forthcoming)..

¶Agriculture emissions are expected to rise almost 30% in the period to 2020; almost two thirds of this increase is expected to come from Africa, Latin America and China. Around half of the projected growth in emissions is expected to come from the use of fertiliser on agricultural soils. There are no available estimates of agriculture emissions to 2050. In recent years, developing countries have accounted for an increasingly large share of agricultural emissions: from two thirds in 1990, to three quarters in 2000, to a projected four fifths in 2020.

¶Figure 2 Agriculture non-CO2 emissions by country (1990-2020)

Drivers behind emissions growth

¶Income and population growth are the key drivers behind growth in agriculture emissions. For example, between 1983-2003, world population rose by 35%, world GDP by 90% and global agricultural output by 52%.⁵⁵ FAOSTAT (2006) Also, as developing countries become richer, more meat is likely to be demanded to the extent that livestock numbers are expected to double by 2020⁶⁶ IPCC (2001); and livestock production is associated with higher emissions than other forms of agriculture. For example, emissions from livestock (enteric fermentation) in China are expected to triple between 1990 and 2020⁷⁷ EPA (forthcoming)..

¶Increased productivity in agriculture is another driver behind emissions growth. In the last 40 years, the area of global agricultural land has grown by 10% but in per capita terms, agricultural land area has been in decline.⁸⁸ FAOSTAT (2006) This trend is expected to continue because there is only limited additional land available (just 11% of world land can be farmed without improvements such as irrigation⁹⁹ FAO (2003).). Also, agriculture will face competition with other potential uses, such as growing of biocrops. This will make it necessary to intensify production by making more use of inputs such as fertilizers. For example, in Asia, synthetic nitrogen fertiliser use increased by a factor of c.19 and nitrous oxide emissions rose around 250%.¹⁰¹⁰ Mosier and Zhu (2000) Requirements for greater productivity and the increased commercialization of production in Asia and Latin America¹¹¹¹ EPA (forthcoming) make it likely that upstream CO2 emissions from electricity and other energy consumption may increase. Note that it can be possible to increase agricultural productivity and reduce emissions at the same time using sustainable farming practices; this is discussed in chapter 25, box 25.4 and annex 7.f on land use change.

Prospects for cutting emissions

¶Compared to the other sectors, relatively little work has been done on how to cut emissions from the agriculture sector. The IPCC has identified around 1 GtCO2e of non-CO2 emission savings from the sector by 2020 at $25/tCO2e¹²¹² IPCC (2001). As quoted in chapter 9, table 9.1., but more recent work suggests this could be lower, around 0.2 GtCO2e per annum in 2030 at $20/tCO2e¹³¹³ Smith et al (forthcoming).. The means of achieving these non-CO2 emission reductions are discussed below:• Methane emissions from rice can be cut by reducing the levels of decomposition occurring in anaerobic conditions. This can be done using measures such as controlled irrigation and better nutrient management. In the next decade or so exploitation of new, higher yielding, crop varieties could also contribute to methane reductions. The IPCC identified about 0.5 GtCO2e per annum savings from rice by 2020 at $27/tCO2e¹⁴¹⁴ IPCC (2001)..

¶• Nitrous oxide emissions from fertilisers could be reduced by making more efficient use of fertilisers.

¶• Methane emissions from livestock could be cut using nutritional supplements, preventing overgrazing, different feeding patterns (such as smaller but more frequent feeding), and research into different livestock breeds¹⁵¹⁵ IPCC (2001) and FAO (2003)..

¶• Methane emissions from manure could be cut by switching to waste management practices that favour aerobic decomposition. Alternatively, capturing methane emissions by storing wastes in an anaerobic environment can be a particularly good way of making emissions savings because the methane (biogas) can be used as an energy source (see chapter 17, box 17.7).¹⁶¹⁶ ECI (2002).

¶• Stopping burning of crop residues would reduce methane and nitrous oxide emissions from this practice.

¶Agricultural land management practices (e.g. crop tilling practices) could be an important source of CO2 emission savings. The IPCC estimate that savings here could amount to 1 to 2 GtCO2 in 2020 at up to $27/tCO2¹⁷¹⁷ IPCC (2001) estimated that 1 GCO2 per annum could be saved from land management practices at $27/tCO2 in 2020. Smith et al (2006, forthcoming) estimated it could save 1.8 GtCO2 per annum at $20/tCO2 in 2030..

¶The contribution of agriculture to climate change can also be reduced by tackling its indirect effect on emissions from the power, industry and transport sectors. For example, more efficient machinery and more efficient use of fertiliser will reduce upstream emissions from the power and industry sectors.

¶Also, giving consumers more information about their food and how far it has travelled to reach them may change their preferences towards buying locally sourced produce, and so reduce upstream transport emissions.

¶By-products from agriculture can also contribute to emission reductions. For example, biomass can be used directly in agriculture as a fertiliser, or it can be used as a source of energy for the power, buildings, industry or transport sectors (as discussed in chapter 9, box 9.5). Biogas from animal wastes could also be used as an energy source (as discussed in chapter 17, box 17.7). Agricultural by-products could also potentially displace some fossil-fuel based inputs for the chemicals, pharmaceuticals, manufacturing and buildings industries.

References

¶EPA (forthcoming) 'Global Anthropogenic non-CO2 greenhouse gas emissions: 1990-2020', US Environmental Protection Agency, Washington DC. Emissions data obtained from correspondence with EPA team.

¶Environmental Change Institute (2004), 'Methane UK', Environmental Change Institute: Oxford, United Kingdom. Available at: http://www.eci.ox.ac.uk/research/energy/methaneuk.php

¶FAO (2003) 'World Agriculture: towards 2015/2030', Earthscan: United Kingdom. Available at: http://www.fao.org/docrep/005/y4252e/y4252e00.htm

¶FAOSTAT (2006) FAO Statistics on-line database, available at http://faostat.fao.org/site/291/default.aspx

¶Intergovernmental Panel on Climate Change (2001): Climate Change 2001: 'Mitigation', Contribution of Working Group III to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Metz B, Davidson O, Swart R and Pan J (eds.)], Cambridge: Cambridge University Press

¶Mosier, A. R. and Zhu, Z. L. (2000) 'Changes in patterns of fertiliser nitrogen use in Asia and its consequences for N2O emissions from agriculture systems', Nutrient Cycling in Agroecosystems, vol 57, no 1, pp107-117.

¶Smith, P., D. Martino, Z. Cai, et al (2006 in press): 'Greenhouse-gas mitigation in agriculture', Philosophical Transactions of the royal Society, B. WRI (2005) 'Navigating the Numbers', World Resources Institute, Washington DC

¶WRI (2006) Climate Analysis Indicators Tool (CAIT) on-line database version 3.0., Washington DC: World Resources Institute, available at http://cait.wri.org

Notes not linked in the text

These notes appear in the source but the pipeline could not place their reference in the body. They are listed here so nothing is lost.

¹ The comments have reached us in various ways – via remarks at seminars, e-mails and press comments. We focus here on the most commonly expressed concerns.
² Discussed in Section 1.4
³ Note that TR in the model is actually the 'vulnerable' temperature increase, as it is assumed that most regions can adapt to some degree of temperature rise. The regional temperature increase is dependent on the global temperature increase (a linear relationship) and the regional sulphate aerosol concentration.
⁴ The parameter can be interpreted as switched 'off' for models where no account is taken of revenues (effectively only the changes in relative prices are modelled) and 'on' for models where the revenues are recycled in some way. Unfortunately, the data underpinning this parameter are thin: among the IMCP models, only E3MG models the use of revenues at all.
⁴ Warren et al. (2006)
⁵ This is on top of the sharply increasing relationship between sea surface temperature and hurricane wind speed.
⁶ This measures how fast the value of an increment in consumption falls as consumption rises, for example when it is equal to one, an extra unit to Person A, with three times the consumption of Person B, would have one third the value to that if the extra unit went to Person B. If the elasticity were equal to two, the extra unit would have one ninth of the value.
⁷ Pearce and Ulph (1999); Stern (1977).
⁸ It is possible to argue that this type of risk should be embodied in the measurement of costs and benefits but it would play a similar computational role and this type of discounting and pure time preferences seems often to be combined.
⁹ In 1990 US $
⁹ http://www.ft.com/cms/s/444ff4ae-783c-11db-be09-0000779e2340.html
¹⁰ Problematic as based on Market Exchange Rates
²⁵ For explanation of how BAU emissions were calculated, see Chapter 7.