finding 7.3 : rising-carbon-dioxide-lowers-nutritional-value-of-food

The nutritional value of agriculturally important food crops, such as wheat and rice, will decrease as rising levels of atmospheric carbon dioxide continue to reduce the concentrations of protein and essential minerals in most plant species [Very Likely, High Confidence].

This finding is from chapter 7 of The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment.

Process for developing key messages: The chapter was developed through technical discussions of relevant evidence and expert deliberation by the report authors at several workshops, teleconferences, and email exchanges. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, and Federal agencies. For additional information on the overall report process, see Appendices 2 and 3. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Accounts associated with each Key Finding.

Because the impacts of climate change on food production, prices, and trade for the United States and globally have been widely examined elsewhere, including in the most recent report from the Intergovernmental Panel on Climate Change,fcd24eab-974a-46aa-8434-78b8cd3f0ef0 c04c5716-c318-4a4c-9774-ae61ce97d305 d0c735f3-4b2c-4dec-907c-09e81818b288 67bff3c8-bddd-4bbb-975d-bec307df5f72 3baf471f-751f-4d68-9227-4197fdbb6e5d c390e13f-8517-40a9-a236-ac4dede3a7a0 this chapter focuses only on the impacts of climate change on food safety, nutrition, and distribution in the context of human health in the United States. Many nutritional deficiencies and food-related illnesses are of critical importance globally, particularly those causing diarrheal epidemics or mycotoxin poisoning, and affect U.S. interests abroad; but the primary focus of this chapter is to address climate impacts on the food safety concerns most important in the United States. Thus, the literature cited in this chapter is specific to the United States or of demonstrated relevance to developed countries. The placement of health threats from seafood was determined based on pre- and post-ingestion risks: while ingestion of contaminated seafood is discussed in this chapter, details on the exposure pathways of water-related pathogens (for example, through recreational or drinking water) are discussed in Chapter 6: Water-Related Illness.

Description of evidence base: The nutritional response of crops to rising carbon dioxide is well documented, particularly among C3 cereals such as rice and wheat, which make up the bulk of human caloric input. C3 species are about 95% of all plant species and represent those species most likely to respond to an increase in atmospheric CO2 concentrations.

There is strong evidence and consensus that protein concentrations in plants strongly correlate with nitrogen concentrations. CO2-induced declines in nitrogen concentrations have been observed in nearly a hundred individual studies and several meta-analyses.de07adc8-7f48-4455-8b2a-6707520acd59 25f24b69-e072-4bba-9a18-282938f62190 31ae7e0e-a0fc-44c4-ac4f-0070aae519a6 1e90a679-d2ce-4cd4-85f3-2cbb63939d35 1f461bf1-02cd-49d5-973b-32961301ddff A meta-analysis of the effect of CO2 on protein by crop covers 228 observations on wheat, rice, soybeans, barley and potato, 6f0fe842-95ce-481a-b3f6-473975719843 and was recently repeated for the United States, Japan, and Australia,7287b49d-8c0d-4f11-95f2-c565c2dd2ee9 covering 138 mean observations on nitrogen/protein in wheat, rice, peas, maize, and sorghum. There is very strong evidence that rising CO2 reduces protein content in non-leguminous C3 crops, including wheat, rice, potato, and barley. There is also good agreement across studies that the ongoing increase in CO2 elevates the overall carbohydrate content in C3 plants.de07adc8-7f48-4455-8b2a-6707520acd59

Another meta-analysis quantifies the role of increasing CO2 in altering the ionome (the mineral nutrient and trace element composition of an organism) of plants, including major crops.de07adc8-7f48-4455-8b2a-6707520acd59 This meta-analysis of 7,761 observations indicates that increasing CO2 also significantly reduces the mineral concentrations (calcium, magnesium, iron, zinc, copper, sulfur, potassium, and phosphorus) in C3 plants, including grains and edible parts of other crops, while also substantially increasing the ratio of total non-structural carbohydrates (starch and sugars) to minerals and to protein.

Furthermore, these studies show the quality of current crops to be lower relative to the crops raised in the past with respect to protein and minerals.de07adc8-7f48-4455-8b2a-6707520acd59 6f0fe842-95ce-481a-b3f6-473975719843 Direct experimental evidence shows that protein concentrations in wheat flour progressively declined with rising CO2 concentrations representing levels in 1900 (approximately 290 ppm), 2008 (approximately 385 ppm), and the CO2 concentrations projected to occur later in this century (approximately 715 ppm).d763a364-656a-4a46-96cc-82800edc3ac2

New information and remaining uncertainties: While the general response and the direction in the change of crop quality is evident; there is uncertainty in the extent of variation in both protein and ionome among different crop varieties. There is little evidence regarding the CO2 effects on complex micronutrients such as carotenoids (vitamin A, lutein, and zeaxanthin). Although protein, micronutrients, and ratio of carbohydrates to protein are all essential aspects of human dietary needs, the projected human health impacts of nutritional changes with increasing CO2 are still being evaluated. There remains a high level of uncertainty regarding how reductions in crop quality affect human nutrition by contributing to or aggravating existing chronic dietary deficiencies and obesity risks, particularly in the United States where dietary protein deficiencies are uncommon.

Assessment of confidence based on evidence: Based on the evidence, there is high confidence that the rapid increase in atmospheric CO2 has resulted in a reduction in the level of protein and minerals relative to the amount of carbohydrates present for a number of important crop species (including a number of globally important cereals such as wheat, barley and rice), and will very likely continue to do so as atmospheric CO2 concentration continues to rise.

References :

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