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

==== 5.6.3.1 Can dietary shifts provide significant benefits? ====

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Many studies now indicate that dietary shifts can significantly reduce GHG emissions. For instance, several studies highlight that if current dietary trends are maintained, this could lead to emissions from agriculture of approximately 20 GtCO <sub>2</sub> -eq yr <sup>–1</sup> by 2050, creating significant mitigation potential (Pradhan et al. 2013b <sup>[[#fn:r1036|1036]]</sup> ; Bajželj et al. 2014 <sup>[[#fn:r1037|1037]]</sup> ; Hedenus et al. 2014 <sup>[[#fn:r1038|1038]]</sup> ; Bryngelsson et al. 2017 <sup>[[#fn:r1039|1039]]</sup> ). Additionally in the USA, a shift in consumption towards a broadly healthier diet, combined with meeting the USDA and Environmental Protection Agency’s 2030 food loss and waste reduction goals, could increase per capita food-related energy use by 12%, decrease blue water consumption by 4%, decrease green water use by 23%, decrease GHG emissions from food production by 11%, decrease GHG emissions from landfills by 20%, decrease land use by 32%, and increase fertiliser use by 12% (Birney et al. 2017 <sup>[[#fn:r1040|1040]]</sup> ). This study, however, does not account for all potential routes to emissions, ignoring, for example, fertiliser use in feed production. Similar studies have been conducted, for China (Li et al. 2016 <sup>[[#fn:r1041|1041]]</sup> ), where adoption of healthier diets and technology improvements have the potential to reduce food systems GHG emissions by &gt;40% relative to those in 2010; and India (Green et al. 2017 <sup>[[#fn:r1042|1042]]</sup> ; Vetter et al. 2017 <sup>[[#fn:r1043|1043]]</sup> ), where alternative diet scenarios can affect emissions from the food system by –20 to +15%.

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Springmann et al.(2018a) modelled the role of technology, waste reduction and dietary change in living within planetary boundaries (Rockström et al. 2009 <sup>[[#fn:r1044|1044]]</sup> ), with the climate change boundary being a 66% chance of limiting warming to less than 2°C. They found that all are necessary for the achievement of a sustainable food system. Their principal conclusion is that only by adopting a ‘flexitarian diet’, as a global average, would climate change be limited to under two degrees. Their definition of a flexitarian diet is fruits and vegetables, plant-based proteins, modest amounts of animal-based proteins, and limited amounts of red meat, refined sugar, saturated fats, and starchy foods.

Healthy and sustainable diets address both health and environmental concerns (Springmann et al. 2018b <sup>[[#fn:r1045|1045]]</sup> ). There is high agreement that there are significant opportunities to achieve both objectives simultaneously. Contrasting results of marginal GHG emissions, that is, variations in emissions as a result of variation in one or more dietary components, are found when comparing low to high emissions in self-selected diets (diets freely chosen by consumers). Vieux et al. (2013) <sup>[[#fn:r1046|1046]]</sup> found self-selected healthier diets with higher amounts of plant-based food products did not result in lower emissions, while (Rose et al. 2019) <sup>[[#fn:r1047|1047]]</sup> found that the lowest emission diets analysed were lower in meat but higher in oil, refined grains and added sugar. Vieux et al. (2018) <sup>[[#fn:r1048|1048]]</sup> concluded that setting nutritional goals with no consideration for the environment may increase GHG emissions.

Tukker et al. (2011) <sup>[[#fn:r1049|1049]]</sup> also found a slight increase in emissions by shifting diets towards the European dietary guidelines, even with lower meat consumption. Heller and Keoleian (2015) <sup>[[#fn:r1050|1050]]</sup> found a 12% increase in GHG emissons when shifting to iso-caloric diets, defined as diets with the same caloric intake of diets currently consumed, following the USA guidelines and a 1% decrease in GHG emissions when adjusting caloric intake to recommended levels for moderate activity. There is scarce information on the marginal GHG emissions that would be associated with following dietary guidelines in developing countries.

Some studies have found a modest mitigation potential of diet shifts when economic and biophysical systems effects are taken into account in association with current dietary guidelines. Tukker et al. (2011) <sup>[[#fn:r1051|1051]]</sup> , considering economic rebound effects of diet shifts (i.e., part of the gains would be lost due to increased use at lower prices), found maximum changes in emissions of the EU food system of 8% (less than 2% of total EU emissions) when reducing meat consumption by 40 to 58%. Using an economic optimisation model for studying carbon taxation in food but with adjustments of agricultural production systems and commodity markets in Europe, Zech and Schneider (2019) found a reduction of 0.41% in GHG emissions at a tax level of 50 USD per tCO <sub>2</sub> -eq. They estimate a leakage of 43% of the GHG emissions reduced by domestic consumption, (i.e., although reducing emissions due to reducing consumption, around 43% of the emissions would not be reduced because part of the production would be directed to exports).

Studying optimised beef production systems intensification technologies in a scenario of no grasslands area expansion de Oliveira Silva et al. (2016) <sup>[[#fn:r1052|1052]]</sup> found marginal GHG emissions to be negligible in response to beef demand in the Brazilian Cerrado. This was because reducing productivity would lead to increased emission intensities, cancelling out the effect of reduced consumption.

In summary, there is significant potential mitigation ( ''high confidence'' ) arising from the adoption of diets in line with dietary recommendations made on the basis of health. These are broadly similar across most countries. These are typically capped at the number of calories and higher in plant-based foods, such as vegetables, fruits, whole grains, legumes, nuts and seeds, and lower in animal-sourced foods, fats and sugar. Such diets have the potential to be both more sustainable and healthier than alternative diets (but healthy diets are not necessarily sustainable and vice versa). The extent to which the mitigation potential of dietary choices can be realised requires both climate change and health being considered together. Socio-economic (prices, rebound effects), political, and cultural contexts would require significant consideration to enable this mitigation potential to be realised.

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