Editing IPCC:AR6/SRCCL/Chapter-5 (section)

==== 5.5.2.1 Mitigation potential of different diets ====

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A systematic review found that higher consumption of animal-based foods was associated with higher estimated environmental impact, whereas increased consumption of plant-based foods was associated with an estimated lower environmental impact (Nelson et al. 2016 <sup>[[#fn:r871|871]]</sup> ). Assessment of individual foods within these broader categories showed that meat – especially ruminant meat (beef and lamb) – was consistently identified as the single food with the greatest impact on the environment, on a global basis, most often in terms of GHG emissions and/or land use.

Figure 5.12 shows the technical mitigation potentials of some scenarios of alternative diets examined in the literature. Stehfest et al. (2009) <sup>[[#fn:r872|872]]</sup> were among the first to examine these questions. They found that under the most extreme scenario, where no animal products are consumed at all, adequate food production in 2050 could be achieved on less land than is currently used, allowing considerable forest regeneration, and reducing land-based GHG emissions to one third of the reference ‘business-as-usual’ case for 2050, a reduction of 7.8 GtCO <sub>2</sub> -eq yr <sup>-1</sup> . Springmann et al. (2016b) <sup>[[#fn:r873|873]]</sup> recently estimated similar emissions reduction potential of 8 GtCO <sub>2</sub> -eq yr <sup>–1</sup> from a vegan diet without animal-sourced foods. This defines the upper bound of the technical mitigation potential of demand side measures.

Herrero et al. (2016a) <sup>[[#fn:r874|874]]</sup> reviewed available options, with a specific focus on livestock products, assessing technical mitigation potential across a range of scenarios, including ‘no animal products’, ‘no meat’, ‘no ruminant meat’, and ‘healthy diet’ (reduced meat consumption). With regard to ‘credible low-meat diets’, where reduction in animal protein intake was compensated by higher intake of pulses, emissions reductions by 2050 could be in the4.3–6.4GtCO <sub>2</sub> -eqyr <sup>-1</sup> , compared to a business-as-usual scenario.

Of this technical potential, 1–2 GtCO <sub>2</sub> -eq yr <sup>–1</sup> come from reductions of mostly non-CO <sub>2</sub> GHG within the farm gate, while the remainder was linked to carbon sequestration on agricultural lands no longer needed for livestock production. When the transition to a low-meat diet reduces the agricultural area required, land is abandoned, and the re-growing vegetation can take up carbon until a new equilibrium is reached. This is known as the land-sparing effect.

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'''Technical mitigation potential of changing diets by 2050 according to a range of scenarios examined in the literature. Estimates indicate technical potential only and include additional effects of carbon sequestration from land-sparing. Data without error bars are from one study only. All diets need to provide a full complement of nutritional quality, including micronutrients (FAO […]'''
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Technical mitigation potential of changing diets by 2050 according to a range of scenarios examined in the literature. Estimates indicate technical potential only and include additional effects of carbon sequestration from land-sparing. Data without error bars are from one study only. All diets need to provide a full complement of nutritional quality, including micronutrients (FAO et al. 2018 <sup>[[#fn:r1452|1452]]</sup> ).Vegan: Completely plant-based (Springmann et al. 2016b <sup>[[#fn:r1453|1453]]</sup> ; Stehfest et al. 2009 <sup>[[#fn:r1454|1454]]</sup> ).Vegetarian: Grains, vegetables, fruits, sugars, oils, eggs and dairy, and generally at most one serving per month of meat or seafood (Springmann et al. 2016b <sup>[[#fn:r1455|1455]]</sup> ; Tilman and Clark 2014 <sup>[[#fn:r1456|1456]]</sup> ; Stehfest et al. 2009 <sup>[[#fn:r1457|1457]]</sup> ).Flexitarian: 75% of meat and dairy replaced by cereals and pulses; at least 500 g per day fruits and vegetables; at least 100 g per day of plant-based protein sources; modest amounts of animal-based proteins and limited amounts of red meat (one portion per week), refined sugar (less than 5% of total energy), vegetable oils high in saturated fat, and starchy foods with relatively high glycaemic index (Springmann et al. 2018a <sup>[[#fn:r1458|1458]]</sup> ; Hedenus et al. 2014 <sup>[[#fn:r1459|1459]]</sup> ).Healthy diet: Based on global dietary guidelines for consumption of red meat, sugar, fruits and vegetables, and total energy intake (Springmann et al. 2018a <sup>[[#fn:r1460|1460]]</sup> ; Bajželj et al. 2014 <sup>[[#fn:r1461|1461]]</sup> ).Fair and frugal: Global daily per-capita calorie intake of 2800 kcal/cap/day (11.7 MJ/cap/day), paired with relatively low level of animal products (Smith et al. 2013 <sup>[[#fn:r1462|1462]]</sup> ).Pescetarian: Vegetarian diet that includes seafood (Tilman and Clark 2014 <sup>[[#fn:r1463|1463]]</sup> ).Climate carnivore: 75% of ruminant meat and dairy replaced by other meat (Hedenus et al. 2014 <sup>[[#fn:r1464|1464]]</sup> ).Mediterranean: Vegetables, fruits, grains, sugars, oils, eggs, dairy, seafood, moderate amounts of poultry, pork, lamb and beef (Tilman and Clark 2014 <sup>[[#fn:r1465|1465]]</sup> ).

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Other studies have found similar results for potential mitigation linked to diets. For instance, Smith et al. (2013) analysed a dietary change scenario that assumed a convergence towards a global daily per-capita calorie intake of 2800 kcal per person per day (11.7 MJ per person per day), paired with a relatively low level of animal product supply, estimated technical mitigation potential in the range 0.7–7.3 GtCO <sub>2</sub> -eq yr <sup>–1</sup> for additional variants including low or high-yielding bioenergy, 4.6GtCO <sub>2</sub> -eqyr <sup>–1</sup> if spare land is afforested.

Bajželj et al. (2014) <sup>[[#fn:r875|875]]</sup> developed different scenarios of farm systems change, waste management, and dietary change on GHG emissions coupled to land use. Their dietary scenarios were based on target kilocalorie consumption levels and reductions in animal product consumption. Their scenarios were ‘healthy diet’; healthy diet with 2500 kcal per person per day in 2050; corresponding to technical mitigation potentials in the range 5.8 and 6.4 GtCO <sub>2</sub> -eq yr <sup>-1</sup> .

Hedenus et al. (2014) explored further dietary variants based on the type of livestock product. ‘climate carnivore’, in which 75% of the baseline-consumption of ruminant meat and dairy was replaced

by pork and poultry meat, and ‘flexitarian’, in which 75% of the baseline-consumption of meat and dairy was replaced by pulses and cereal products. Their estimates of technical mitigation potentials by 2050 ranged 3.4–5.2 GtCO <sub>2</sub> -eq yr <sup>-1</sup> , the high end achieved under the flexitarian diet. Finally, Tilman and Clark (2014) used stylised diets as variants that included ‘peseatarian’, ‘Mediterranean’, ‘vegetarian’, compared to a reference diet, and estimated technical mitigation potentials within the farm gate of 1.2–2.3 GtCO <sub>2</sub> -eq yr <sup>-1</sup> , with additional mitigation from carbon sequestration on spared land ranging 1.8–2.4 GtCO <sub>2</sub> -eq yr <sup>-1</sup> .

Studies have defined dietary mitigation potential as, for example, 20 kg per person per week CO <sub>2</sub> -eq for Mediterranean diet, versus 13 kg per person per week CO <sub>2</sub> -eq for vegan (Castañé and Antón 2017 <sup>[[#fn:r876|876]]</sup> ). Rosi et al. (2017) <sup>[[#fn:r877|877]]</sup> developed seven-day diets in Italy for about 150 people defined as omnivore 4.0 ± 1.0; ovo-lacto-veggie 2.6 ± 0.6; and vegan 2.3 ± 0.5 kg CO <sub>2</sub> -eq per capita per day.

Importantly, many more studies that compute the economic and calorie costs of these scenarios are needed. Herrero et al. (2016a) <sup>[[#fn:r878|878]]</sup> estimated that once considerations of economic and calorie costs of their diet-based solutions were included, the technical range of 4.3–6.4 GtCO <sub>2</sub> -eq yr <sup>–1</sup> in 2050 was reduced to 1.8–3.4 GtCO <sub>2</sub> -eq yr <sup>–1</sup> when implementing a GHG tax ranging from 20–100 USD tCO <sub>2</sub> . While caloric costs where low below 20 USD tCO <sub>2</sub> , they ranged from 27–190 kcal per person per day under the higher economic potential, thus indicating possible negative trade-offs with food security.

In summary, demand-side changes in food choices and consumption can help to achieve global GHG mitigation targets ( ''high confidence'' ). Low-carbon diets on average tend to be healthier and have smaller land footprints. By 2050, technical mitigation potential of dietary changes range from 2.7–6.4 GtCO <sub>2</sub> -eq yr <sup>–1</sup> for assessed diets ( ''high confidence'' ). At the same time, the economic potential of such solutions is lower, ranging from 1.8–3.4 GtCO <sub>2</sub> -eq yr <sup>–1</sup> at prices of 20–100 USD tCO <sub>2</sub> , with caloric costs up to 190 kcal per person per day. The feasibility of how to create economically viable transitions to more sustainable and healthy diets that also respect food security requirements needs to be addressed in future research.

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