(Fischedick et al. 2014), we estimated their total contribution to be roughly 10% of total anthropogenic emissions (Table 5.4). There is no post-AR5 assessment at the global level in terms of absolute emissions. Rather, several studies have recently investigated how the combined emissions within and outside the farm gate are embedded in food products and thus associated with specific dietary choices (see next section). Below important components of food systems emissions beyond the farm gate are discussed based on recent literature. Refrigerated trucks, trailers, shipping containers, warehouses, and retail displays that are vital parts of food supply chains all require energy and are direct sources of GHG emissions. Upstream emissions in terms of feed and fertiliser manufacture and downstream emissions (transport, refrigeration) in intensive livestock production (dairy, beef, pork) can account for up to 24–32% of total livestock emissions, with the higher fractions corresponding to commodities produced by monogastric animals (Weiss and Leip 2012). The proportion of upstream/downstream emissions fall significantly for less-intensive and more-localised production systems (Mottet et al. 2017a).
Transport and processing. Recent globalisation of agriculture
has promoted industrial agriculture and encouraged value-added processing and more distant transport of agricultural commodities, all leading to increased GHG emissions. Although often GHG-intensive, food transportation plays an important role in food chains: it delivers food from producers to consumers at various distances, particularly to feed people in food-shortage zones from food-surplus zones. (Section 5.5.2.6 for assessment of local food production.)
To some extent, processing is necessary in order to make food supplies more stable, safe, long-lived, and in some cases, nutritious (FAO 2007). Agricultural production within the farm gate may contribute 80–86% of total food-related emissions in many countries, with emissions from other processes such as processing and transport being small (Vermeulen et al. 2012). However, in net food-importing countries where consumption of processed food is common, emissions from other parts of the food lifecycle generated in other locations are much higher (Green et al. 2015).
A study conducted by Wakeland et al. (2012) in the USA found that the transportation-related carbon footprint varies from a few percent to more than half of the total carbon footprint associated with food production, distribution, and storage. Most of the GHGs emitted from food processing are a result of the use of electricity, natural gas, coal, diesel, gasoline or other energy sources. Cookers, boilers, and furnaces emit carbon dioxide, and wastewater emits methane and nitrous oxide. The most energy-intensive processing is wet milling of maize, which requires 15% of total USA food industry energy (Bernstein et al. 2008); processing of sugar and oils also requires large amounts of energy.
5.4.6 Greenhouse gas emissions associated with different diets
There is now extensive literature on the relationship between food products and emissions, although the focus of the studies has been on high-income countries. Godfray et al. (2018) updated Nelson et al. (2016), a previous systematic review of the literature on environmental impacts associated with food, and concluded that higher consumption of animal-based foods was associated with higher estimated environmental impacts, whereas increased consumption of plant-based foods was associated with estimated lower environmental impact. Assessment of individual foods within these broader categories showed that meat – sometimes specified as ruminant meat (mainly beef) – was consistently identified as the single food with the greatest impact on the environment, most often in terms of GHG emissions and/or land use per unit commodity. Similar hierarchies, linked to well-known energy losses along trophic chains, from roots to beef were found in another recent review focussing exclusively on GHG emissions (Clune et al. 2017), and one on life-cycle assessments (Poore and Nemecek 2018). Poore and Nemecek (2018) amassed an extensive database that specifies both the hierarchy of emissions intensities and the variance with the production context (for example, by country and farming system). The emissions intensities of red meat mean that its production has a disproportionate impact on total emissions (Godfray et al. 2018). For example, in the USA 4% of food sold (by weight) is beef, which accounts for 36% of food-related emissions (Heller and Keoleian 2015). Food-related emissions are therefore very sensitive to the amount and type of meat consumed. However, 100 g of beef has twice as much protein as the equivalent in cooked weight of beans, for example, and 2.5 times more iron. One can ingest only about 2.5 kg of food per day and not all food items are as dense in nutrition.
There is therefore robust evidence with high agreement that the mixture of foods eaten can have a highly significant impact on per capita carbon emissions, driven particularly through the amount of (especially grain-fed) livestock and products.
Given the rising costs of malnutrition in all its forms, a legitimate question is often asked: would a diet that promotes health through good nutrition also be one that mitigates GHG emissions? Whilst sustainable diets need not necessarily provide more nutrition, there is certainly significant overlap between those that are healthier (e.g., via eating more plant-based material and less livestock-based material), and eating the appropriate level of calories. In their systematic review, Nelson et al. (2016) conclude that, in general, a dietary pattern that is higher in plant-based foods, such as vegetables, fruits, whole grains, legumes, nuts, and seeds, and lower in animal-based foods is more health-promoting and is associated with lesser environmental impact (GHG emissions and energy, land, and water use) than is the current average ‘meat-based’ diet.
Recent FAO projections of food and agriculture to 2050 under alternative scenarios characterised by different degrees of sustainability, provide global-scale evidence that rebalancing diets is key to increasing the overall sustainability of food and agricultural
5
systems world-wide. A 15% reduction of animal products in the diets of high-income countries by 2050 would contribute to containing the need to expand agricultural output due to upward global demographic trends. Not only would GHG emissions and the pressure on land and water be significantly reduced but the potential for low-income countries to increase the intake of animal-based food, with beneficial nutritional outcomes, could be enhanced (FAO 2018a). Given that higher-income countries typically have higher emissions per capita, results are particularly applicable in such places.
However, Springmann et al. (2018a) found that there are locally applicable upper bounds to the footprint of diets around the world, and for lower-income countries undergoing a nutrition transition, adopting ‘Westernised’ consumption patterns (over-consumption, large amounts of livestock produce, sugar and fat), even if in culturally applicable local contexts, would increase emissions. The global mitigation potential of healthy but low-emissions diets is discussed in detail in Section 5.5.2.1.
In summary, food system emissions are growing globally due to increasing population, income, and demand for animal-sourced products (high confidence). Diets are changing on average toward greater consumption of animal-based foods, vegetable oils and sugar/sweeteners (high confidence) (see also Chapter 2), with GHG emissions increasing due to greater amounts of animal-based products in diets (robust evidence, medium agreement).
5.5
Mitigation options, challenges
and opportunities
The IPCC AR5 WG III concluded that mitigation in agriculture, forestry, and land use (AFOLU) is key to limit climate change in the 21st century, in terms of mitigation of non-CO2 GHGs, which are predominately emitted in AFOLU, as well as in terms of land-based carbon sequestration. Wollenberg et al. (2016) highlighted the need to include agricultural emissions explicitly in national mitigation targets and plans, as a necessary strategy to meet the 2°C goal of the Paris Agreement. This chapter expands on these key findings to document how mitigation in the entire food system, from farm gate to consumer, can contribute to reaching the stated global mitigation goals, but in a context of improved food security and nutrition. To put the range of mitigation potential of food systems in context, it is worth noting that emissions from crop and livestock are expected to increase by 30–40% from present to 2050, under business-as-usual scenarios that include efficiency improvements as well as dietary changes linked to increased income per capita (FAO 2018a; Tubiello et al. 2014). Using current emissions estimates in this chapter and Chapter 2, these increases translate into projected GHG emissions from agriculture of 8–9 Gt CO2-eq yr–1 by 2050 (medium confidence). The AR5 ranked mitigation measures from simple mechanisms such as improved crop and livestock management (Smith et al. 2014) to more complex carbon dioxide reduction interventions, such as afforestation, soil carbon storage and biomass energy projects with carbon capture and storage (BECCS). The AR5 WGIII AFOLU chapter
(Smith et al. 2014) identified two primary categories of mitigation pathways from the food system:
Supply side: Emissions from agricultural soils, land-use change, land
management, and crop and livestock practices can be reduced and terrestrial carbon stocks can be increased by increased production efficiencies and carbon sequestration in soils and biomass, while emissions from energy use at all stages of the food system can be reduced through improvements in energy efficiency and fossil fuel substitution with carbon-free sources, including biomass.
Demand side: GHG emissions could be mitigated by changes in diet,
reduction in food loss and waste, and changes in wood consumption for cooking.
In this chapter, supply-side mitigation practices include land-use change and carbon sequestration in soils and biomass in both crop and livestock systems. Cropping systems practices include improved land and fertiliser management, land restoration, biochar applications, breeding for larger root systems, and bridging yield gaps (Dooley and Stabinsky 2018). Options for mitigation in livestock systems include better manure management, improved grazing land management, and better feeding practices for animals. Agroforestry also is a supply-side mitigation practice. Improving efficiency in supply chains is a supply-side mitigation measure.
Demand-side mitigation practices include dietary changes that lead to reduction of GHG emissions from production and changes in land use that sequester carbon. Reduction of food loss and waste can contribute to mitigation of GHGs on both the supply and demand sides. See Section 5.7 and Chapter 7 for the enabling conditions needed to ensure that these food system measures would deliver their potential mitigation outcomes.
5.5.1 Supply-side mitigation options
The IPCC AR5 identified options for GHG mitigation in agriculture, including cropland management, restoration of organic soils, grazing land management and livestock, with a total mitigation potential of 1.6–4.6 GtCO2-eq yr–1 by 2030 (compared to baseline emissions in the same year), at carbon prices from 20 to 100 USD per tCO2-eq (Smith et al. 2014). Reductions in GHG emissions intensity (emissions per unit product) from livestock and animal products can also be a means to achieve reductions in absolute emissions in specific contexts and with appropriate governance (medium confidence). Agroforestry mitigation practices include rotational woodlots, long-term fallow, and integrated land use.
Emissions from food systems can be reduced significantly by the implementation of practices that reduce carbon dioxide, methane, and nitrous oxide emissions from agricultural activities related to the production of crops, livestock, and aquaculture. These include implementation of more sustainable and efficient crop and livestock production practices aimed at reducing the amount of land needed per output (reductions in GHG emissions intensity from livestock and animal production can support reductions in absolute emissions if