Rise in CO2 levels cutting dietary protein in staple crops

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If CO2 levels continue to rise as projected, the populations of 18 countries may lose more than 5% of their dietary protein by 2050 due to a decline in the nutritional value of rice, wheat, and other staple crops, according to findings from Harvard TH Chan School of Public Health. Researchers estimate that roughly an additional 150m people may be placed at risk of protein deficiency because of elevated levels of CO2 in the atmosphere. This is the first study to quantify this risk.

“This study highlights the need for countries that are most at risk to actively monitor their populations’ nutritional sufficiency, and, more fundamentally, the need for countries to curb human-caused CO2 emissions,” said Samuel Myers, senior research scientist in the department of environmental health.

Globally, 76% of the population derives most of their daily protein from plants. To estimate their current and future risk of protein deficiency, the researchers combined data from experiments in which crops were exposed to high concentrations of CO2 with global dietary information from the United Nations and measures of income inequality and demographics.

They found that under elevated CO2 concentrations, the protein contents of rice, wheat, barley, and potatoes decreased by 7.6%, 7.8%, 14.1%, and 6.4%, respectively. The results suggest continuing challenges for sub Saharan Africa, where millions already experience protein deficiency, and growing challenges for South Asian countries, including India, where rice and wheat supply a large portion of daily protein. The researchers found that India may lose 5.3% of protein from a standard diet, putting a predicted 53 million people at new risk of protein deficiency.

A companion paper co-authored by Myers, found that CO2-related reductions in iron content in staple food crops are likely to also exacerbate the already significant problem of iron deficiency worldwide. Those most at risk include 354m children under 5 and 1.06bn women of childbearing age – predominantly in South Asia and North Africa – who live in countries already experiencing high rates of anaemia and who are expected to lose more than 3.8% of dietary iron as a result of this CO2 effect.

These two studies, taken alongside an earlier study showing that elevated CO2 emissions are also likely to drive roughly 200m people into zinc deficiency, quantify the significant nutritional toll expected to arise from human-caused CO2 emissions.

“Strategies to maintain adequate diets need to focus on the most vulnerable countries and populations, and thought must be given to reducing vulnerability to nutrient deficiencies through supporting more diverse and nutritious diets, enriching the nutritional content of staple crops, and breeding crops less sensitive to these CO2 effects. And, of course, we need to dramatically reduce global CO2 emissions as quickly as possible,” Myers said.

Funding for the study was provided by the Bill & Melinda Gates Foundation and by the Winslow Foundation.

Abstract
Background: Crops grown under elevated atmospheric CO2 concentrations (eCO2) contain less protein. Crops particularly affected include rice and wheat, which are primary sources of dietary protein for many countries.
Objectives: We aimed to estimate global and country-specific risks of protein deficiency attributable to anthropogenic CO2 emissions by 2050.
Methods: To model per capita protein intake in countries around the world under eCO2, we first established the effect size of eCO2 on the protein concentration of edible portions of crops by performing a meta-analysis of published literature. We then estimated per-country protein intake under current and anticipated future eCO2 using global food balance sheets (FBS).
We modeled protein intake distributions within countries using Gini coefficients, and we estimated those at risk of deficiency from estimated average protein requirements (EAR) weighted by population age structure.
Results: Under eCO2, rice, wheat, barley, and potato protein contents decreased by 7.6%, 7.8%, 14.1%, and 6.4%, respectively. Consequently, 18 countries may lose >5% of their dietary protein, including India (5.3%). By 2050, assuming today’s diets and levels of income inequality, an additional 1.6% or 148.4 million of the world’s population may be placed at risk of protein deficiency because of eCO2. In India, an additional 53 million people may become at risk.
Conclusions: Anthropogenic CO2 emissions threaten the adequacy of protein intake worldwide. Elevated atmospheric CO2 may widen the disparity in protein intake within countries, with plant-based diets being the most vulnerable.

Authors
Danielle E Medek, Joel Schwartz, Samuel S Myers

Abstract 2
Iron deficiency reduces capacity for physical activity, lowers IQ, and increases maternal and child mortality, impacting roughly a billion people worldwide. Recent studies have shown that certain highly consumed crops—C3 grains (e.g., wheat, rice, and barley), legumes, and maize—have lower iron concentrations of 4–10% when grown under increased atmospheric CO2 concentrations (550 ppm). We examined diets in 152 countries globally (95.5% of the population) to estimate the percentage of lost dietary iron resulting from anthropogenic CO2 emissions between now and 2050, specifically among vulnerable age-sex groups: children (1–5 years) and women of childbearing age (15–49 years), holding diets constant. We also cross-referenced these with the current prevalence of anemia to identify most at-risk countries. We found that 1.4 billion children aged 1–5 and women of childbearing age (59% of global total for these groups) live in high-risk countries, where the prevalence of anemia exceeds 20% and modeled loss in dietary iron would be in the most severe tertile (>3.8%). The countries with the highest anemia prevalence also derive their iron from the fewest number of foods, even after excluding countries consuming large amounts of unaccounted wild-harvest foods. The potential risk of increased iron deficiency adds greater incentive for mitigating anthropogenic CO2 emissions and highlights the need to address anticipated health impacts via improved health delivery systems, dietary behavioral changes, or agricultural innovation. Because these are effects on content rather than yield, it is unlikely that consumers will perceive this health threat and adapt to it without education.

Authors
MR Smith, CD Golden, SS Myers

Harvard TH Chan School of Public Health material
Environmental Health Perspectives abstract
GeoHealth abstract


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