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

=== 5.2.4 Climate change impacts on food utilisation ===

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Food utilisation involves nutrient composition of food, its preparation, and overall state of health. Food safety and quality affects food utilisation.

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==== 5.2.4.1 Impacts on food safety and human health ====

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Climate change can influence food safety through changing the population dynamics of contaminating organisms due to, for example, changes in temperature and precipitation patterns, humidity, increased frequency and intensity of extreme weather events, and changes in contaminant transport pathways. Changes in food and farming systems, for example, intensification to maintain supply under climate change, may also increase vulnerabilities as the climate changes (Tirado et al. 2010 <sup>[[#fn:r411|411]]</sup> ).

Climate-related changes in the biology of contaminating organisms include changing the activity of mycotoxin-producing fungi, changing the activity of microorganisms in aquatic food chains that cause disease (e.g., dinoflagellates, bacteria like ''Vibrio'' ), and increasingly heavy rainfall and floods causing contamination of pastures with enteric microbes (like ''Salmonella'' ) that can enter the human food chain. Degradation and spoilage of products in storage and transport can also be affected by changing humidity and temperature outside of cold chains, notably from microbial decay but also from potential changes in the population dynamics of stored product pests (e.g., mites, beetles, moths) (Moses et al. 2015 <sup>[[#fn:r412|412]]</sup> ).

Mycotoxin-producing fungi occur in specific conditions of temperature and humidity, so climate change will affect their range, increasing risks in some areas (such as mid-temperate latitudes) and reducing them in others (e.g., the tropics) (Paterson and Lima 2010 <sup>[[#fn:r413|413]]</sup> ). There is ''robust evidence'' from process-based models of particular species ( ''Aspergillus'' /Aflatoxin B1, ''Fusarium'' /deoxynivalenol), which include projections of future climate that show that aflatoxin contamination of maize in Southern Europe will increase significantly (Battilani et al. 2016 <sup>[[#fn:r414|414]]</sup> ), and deoxynivalenol contamination of wheat in Northwestern Europe will increase by up to three times current levels (van der Fels-Klerx et al. 2012b, a) <sup>[[#fn:r1429|1429]]</sup>

Whilst downscaled climate models make any specific projection for a given geography uncertain (Van der Fels-Klerx et al. 2013) <sup>[[#fn:r1430|1430]]</sup> , experimental evidence on the small scale suggests that the combination of rising CO <sub>2</sub> levels, affecting physiological processes in photosynthetic organisms, and temperature changes, can be significantly greater than temperature alone (Medina et al. 2014 <sup>[[#fn:r415|415]]</sup> ). Risks related to aflatoxins are likely to change, but detailed projections are difficult because they depend on local conditions (Vaughan et al. 2016 <sup>[[#fn:r416|416]]</sup> ).

Foodborne pathogens in the terrestrial environment typically come from enteric contamination (from humans or animals), and can be spread by wind (blowing contaminated soil) or flooding – the incidence of both of which are likely to increase with climate change (Hellberg and Chu 2016 <sup>[[#fn:r417|417]]</sup> ). Furthermore, water stored for irrigation, which may be increased in some regions as an adaptation strategy, can become an important route for the spread of pathogens (as well as other pollutants). Contaminated water and diarrheal diseases are acute threats to food security (Bond et al. 2018 <sup>[[#fn:r418|418]]</sup> ). Whilst there is little direct evidence (in terms of modelled projections) the results of a range of reviews, as well as expert groups, suggest that risks from foodborne pathogens are likely to increase through multiple mechanisms (Tirado et al. 2010 <sup>[[#fn:r419|419]]</sup> ; van der Spiegel et al. 2012 <sup>[[#fn:r420|420]]</sup> ; Liu et al. 2013 <sup>[[#fn:r421|421]]</sup> ; Kirezieva et al. 2015 <sup>[[#fn:r422|422]]</sup> ; Hellberg and Chu 2016 <sup>[[#fn:r423|423]]</sup> ).

An additional route to climate change impacts on human health can arise from the changing biology of plants altering human exposure levels. This may include climate changing how crops sequester heavy metals (Rajkumar et al. 2013 <sup>[[#fn:r424|424]]</sup> ), or how they respond to changing pest pressure (e.g., cassava produces hydrogen cyanide as a defence against herbivore attack).

All of these factors will lead to regional differences regarding food safety impacts (Paterson and Lima 2011 <sup>[[#fn:r425|425]]</sup> ). For instance, in Europe it is expected that most important food safety-related impacts will be mycotoxins formed on plant products in the field or during storage; residues of pesticides in plant products affected by changes in pest pressure; trace elements and/or heavy metals in plant products depending on changes in abundance and availability in soils; polycyclic aromatic hydrocarbons in foods following changes in long-range atmospheric transport and deposition; and presence of pathogenic bacteria in foods following more frequent extreme weather, such as flooding and heat waves (Miraglia et al. 2009 <sup>[[#fn:r426|426]]</sup> ).

In summary, there is ''medium evidence,'' with ''high agreement'' that food utilisation via changes in food safety (and potentially food access from food loss) will be impacted by climate change, mostly by increasing risks, but there is ''low confidence'' , exactly how they may change for any given place.

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==== 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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