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Agriculture Mitigation Opportunities Global
Sources: Climate change 2001 Synthesis Report p. 323, Climate Change 2001 Working Group III: Mitigation section 3.6
Agriculture contributes only 4% of global carbon emissions from energy use, but 20% of greenhouse gas emissions.
The greenhouse gases are:
- CH4 (55%60% of total CH4 emissions) from rice paddies, land use change, biomass burning, digestive system fermentation, and animal wastes
- N2O (65%80% of total N2O emissions) mainly from nitrogen fertilizers and animal wastes
- CO2 (21%25% of total CO2 emissions) mainly from deforestation and clearing land and some fossil fuels used on farms
Biotechnology developments could result in increased energy efficiency if concerns about adverse environmental effects are addressed.
It takes much more energy to produce meat for human consumption than plants. With each step up the food chain there is energy loss. If corn is used to feed cattle, only 10% of the energy in the corn is converted into beef. More people can be fed by eating the corn directly rather than converting it to beef first. A shift toward a greater proportion of plants in our diet could greatly increase energy efficiency and decrease greenhouse gas emissions.
In developing countries such as India, emissions mainly arise from cattle methane, field burning of agricultural residues, and paddy cultivation. Methane is produced in the digestive tract of cattle. Rice paddies release methane as bacteria decompose organic material under water. Research into more frequent draining of paddy fields, reduction in the use of nitrogenous fertilizers, and improved diets of cattle is ongoing. However, cattle numbers are expected to increase 50% by 2020, which would largely offset any gains in reducing methane.
In many developing countries, traditional agriculture still depends on human labour and animal power together with firewood for cooking.
In industrialized countries, agriculture relies on burning fossil fuel directly as well as energy used in fertilizer production, and for transportation of products to markets. In the USA each food item purchased has been transported an average of over 2500 km. It is even further in Europe and Australasia. In developed countries the energy required to produce our food and drink is 42 GJ (GigaJoules) per person per year, being 10 times the energy content of the food!
Changes in Agricultural Practices
Major reductions in greenhouse gases can be achieved by 2010 by doing the following:
- Conservation tillage and reducing land use intensity. Conventional tillage burns 60% of the tractor fuel used in industrialized crop production. Minimum and zero cultivation techniques save tractor fuel, conserve soil moisture, and reduce soil erosion.
Overuse of soils leads to degradation, salinization, erosion, and desertification. This reduces the organic matter and increases carbon emissions from the soil. Reducing the intensity of soil cultivation could result in increased organic matter and carbon sequestration (capturing carbon in the soil).
- Methane reduction by rice paddy management and lower emissions from grazing animals. Emissions from rice paddies can be reduced by intermittent flooding and greater use of inorganic fertilizers.
Average methane emissions of grazing animals in temperate regions are 76.8 kg/head/yr for dairy cattle; beef cattle, 67.5kg; deer, 30.6kg; goats, 16.5kg; and sheep, 15.1kg. Emissions can be reduced by chemical, antibiotic control (vaccines) or biological methods (bacteriocins) without affecting animal performance. Poor animal diet in developing countries produces higher methane per unit of production. Selective breeding and magnesium licks may be cheap options. Reduction in livestock numbers because of reduced demand for meat and wool would lower emissions.
- Nitrous oxide reduction. N2O emissions exceed carbon emission from fossil fuels in agriculture. Nitrous oxide emissions (over 800MtC/yr) are released after application of N fertilizers. They can be avoided by using slow release fertilizers, organic manures, nitrification inhibitors and potentially genetically engineered leguminous plants. These strategies could cut emissions by 30% on a global scale.
Increasing energy inputs to meet the growing needs for food and fibre are shown in Figure 1.
Figure 1. Energy use in the agricultural sector from 1971 to 1995. EJ: EtaJoule = 1018 Joules. Source: Climate Change 2001 Working Group III: Mitigation section 3.6
1. Which regions show the greatest increase in agricultural energy use in recent years? Try to account for this increase.
2. What has happened to the energy use in countries with economies in transition? Why do you think this trend has changed? (Economies in Transition are in the process of changing from a planned economic system to a market economy. They include Russia, Poland Ukraine, Czech Republic and others.)