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

==== 5.2.4.2 Impacts on food quality ====

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There are two main routes by which food quality may change. First, the direct effects of climate change on plant and animal biology, such as through changing temperatures changing the basic metabolism of plants. Secondly, by increasing carbon dioxide’s effect on biology through CO <sub>2</sub> fertilisation.

'''Direct effects on plant and animal biology''' . Climate affects a range of biological processes, including the metabolic rate in plants and ectothermic animals. Changing these processes can change growth rates, and therefore yields, but can also cause organisms to change relative investments in growth vs reproduction, and therefore change the nutrients assimilated. This may decrease protein and mineral nutrient concentrations, as well as alter lipid composition (DaMatta et al. 2010 <sup>[[#fn:r427|427]]</sup> ). For example, apples in Japan have been exposed to higher temperatures over 3–4 decades and have responded by blooming earlier. This has led to changes in acidity, firmness, and water content, reducing quality (Sugiura et al. 2013 <sup>[[#fn:r428|428]]</sup> ). In other fruit, such as grapes, warming-induced changes in sugar composition affect both colour and aroma (Mira de Orduña 2010 <sup>[[#fn:r429|429]]</sup> ). Changing heat stress in poultry can affect yield as well as meat quality (by altering fat deposition and chemical constituents), shell quality of eggs, and immune systems (Lara and Rostagno 2013 <sup>[[#fn:r430|430]]</sup> ).

'''Effects of rising CO <sub>2</sub> concentrations''' . Climate change is being driven by rising concentrations of carbon dioxide and other GHG’s in the atmosphere. As plants use CO <sub>2</sub> in photosynthesis to form sugar, rising CO <sub>2</sub> levels, all things being equal, enhances the process unless limited by water or nitrogen availability. This is known as ‘CO <sub>2</sub> fertilisation’. Furthermore, increasing CO <sub>2</sub> allows stomata to partially close during gas exchange, reducing water loss through transpiration. These two factors affect the metabolism of plants, and, as with changing temperatures, affects plant growth rates, yields and their nutritional quality. Studies of these effects include meta-analyses, modelling, and small-scale experiments (Franzaring et al. 2013 <sup>[[#fn:r431|431]]</sup> ; Mishra and Agrawal 2014 <sup>[[#fn:r432|432]]</sup> ; Myers et al. 2014 <sup>[[#fn:r433|433]]</sup> ; Ishigooka et al. 2017 <sup>[[#fn:r434|434]]</sup> ; Zhu et al. 2018 <sup>[[#fn:r435|435]]</sup> ; Loladze 2014 and Yu et al. 2014 <sup>[[#fn:r436|436]]</sup> ).

With regard to nutrient quality, a meta-analysis from seven Free-Air Carbon dioxide Enrichment (FACE), (with elevated atmospheric CO <sub>2</sub> concentration of 546–586 ppm) experiments (Myers et al. 2014), found that wheat grains had 9.3% lower zinc (CI 5.9–12.7%), 5.1% lower iron (CI 3.7–6.5%) and 6.3% lower protein (CI 5.2–7.5%), and rice grains had 7.8% lower protein content (CI 6.8–8.9%). Changes in nutrient concentration in field pea, soybean and C4 crops such as sorghum and maize were small or insignificant. Zhu et al. (2018) <sup>[[#fn:r437|437]]</sup> report a meta-analysis of FACE trials on a range of rice cultivars. They show that protein declines by an average of 10% under elevated CO <sub>2</sub> , iron and zinc decline by 8% and 5% respectively. Furthermore, a range of vitamins show large declines across all rice cultivars, including B1 (–17%), B2 (–17%), B5 (–13%) and B9 (–30%), whereas vitamin E increased. As rice underpins the diets of many of the world’s poorest people in low-income countries, especially in Asia, Zhu et al. (2018) estimate that these changes under high CO <sub>2</sub> may affect the nutrient status of about 600 million people.

Decreases in protein concentration with elevated CO <sub>2</sub> are related to reduced nitrogen concentration possibly caused by nitrogen uptake not keeping up with biomass growth, an effect called ‘carbohydrate dilution’ or ‘growth dilution’, and by inhibition of photorespiration which can provide much of the energy used for assimilating nitrate into proteins (Bahrami et al. 2017 <sup>[[#fn:r438|438]]</sup> ). Other mechanisms have also been postulated (Feng et al. 2015 <sup>[[#fn:r439|439]]</sup> ; Bloom et al. 2014 <sup>[[#fn:r440|440]]</sup> ; Taub and Wang 2008 <sup>[[#fn:r441|441]]</sup> ). Together, the impacts on protein availability may take as many as 150 million people into protein deficiency by 2050 (Medek et al. 2017 <sup>[[#fn:r442|442]]</sup> ). Legume and vegetable yields increased with elevated CO <sub>2</sub> concentration of 250 ppm above ambient by 22% (CI 11.6–32.5%), with a stronger effect on leafy vegetables than on legumes and no impact for changes in iron, vitamin C or flavonoid concentration (Scheelbeek et al. 2018 <sup>[[#fn:r443|443]]</sup> ).

Increasing concentrations of atmospheric CO <sub>2</sub> lower the content of zinc and other nutrients in important food crops. Dietary deficiencies of zinc and iron are a substantial global public health problem (Myers et al. 2014 <sup>[[#fn:r444|444]]</sup> ). An estimated two billion people suffer these deficiencies (FAO 2013a <sup>[[#fn:r445|445]]</sup> ), causing a loss of 63million life-years annually (Myers et al. 2014 <sup>[[#fn:r446|446]]</sup> ). Most of these people depend on C3 grain legumes as their primary dietary source of zinc and iron. Zinc deficiency is currently responsible for large burdens of disease globally, and the populations who are at highest risk of zinc deficiency receive most of their dietary zinc from crops (Myers et al. 2015 <sup>[[#fn:r447|447]]</sup> ). The total number of people estimated to be placed at new risk of zinc deficiency by 2050 is 138 million. The people likely to be most affected live in Africa and South Asia, with nearly 48 million residing in India alone. Differences between cultivars of a single crop suggest that breeding for decreased sensitivity to atmospheric CO <sub>2</sub> concentration could partly address these new challenges to global health (Myers et al. 2014 <sup>[[#fn:r448|448]]</sup> ).

In summary, while increased CO <sub>2</sub> is projected to be beneficial for crop productivity at lower temperature increases, it is projected to lower nutritional quality (e.g., less protein, zinc, and iron) ( ''high confidence'' ).

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