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Harvard researchers say climate change will impact diets of millions worldwide

Matthew Cavanaugh for The Boston Globe

Wheat from Four Stars Farm in Northfield, Mass. Wheat and other crops will become less nutritious as carbon dioxide levels rise, Harvard researchers said.

By Globe Staff 

Harvard researchers say rising levels of carbon dioxide are going to have an impact in a place you might not expect: hundreds of millions of people’s diets worldwide, which will become less nutritious.

Crops such as rice and wheat become less nutritious when carbon dioxide levels are higher, the researchers from the Harvard T.H. Chan School of Public Health said in a statement.

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The researchers said that humans tend to get most of their key nutrients from plants — 63 percent of their protein, 81 percent of their iron, and 68 percent of their zinc. Crops provide less of those nutrients when carbon dioxide is higher.

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An Afghan farmer harvests wheat on the outskirts of Mazar-i-Sharif

Under current conditions, carbon dioxide levels are just above 400 parts per million. But by the middle of this century, carbon dioxide concentrations, which are rising due to human activity, are expected to reach around 550 parts per million, researchers said.

The researchers estimated that, at that point, 175 million people could become deficient in zinc, and 122 million people could become protein-deficient. Researchers also said 1.4 billion women of child-bearing age and children under 5 who are now at high risk of iron deficiency could have their iron intakes reduced by 4 percent or more.

“Our research makes it clear that decisions we are making every day — how we heat our homes, what we eat, how we move around, what we choose to purchase — are making our food less nutritious and imperiling the health of other populations and future generations,” Sam Myers, lead author of the study and principal research scientist at the school, said in the statement.

The study, which was published Aug. 27 in the journal Nature Climate Change, built on previous research that looked at fewer foods and fewer countries, researchers said.

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The rise in carbon dioxide “is likely to reduce the dietary supply of nutrients for many populations and increase the prevalence of global nutritional insufficiency. . . . This is particularly concerning as over two billion people are currently estimated to be deficient in one or more nutrients,” the study said.

India would be the hardest-hit area, along with other countries in Asia, Africa, and the Middle East, researchers said.

“We cannot disrupt most of the biophysical conditions to which we have adapted over millions of years without unanticipated impacts on our own health and well-being,” said Myers.

The impact on the nutritional value of crops is a less-discussed impact of climate change, which is expected to, among other things, increase temperatures, lengthen growing seasons, change precipitation patterns, create more droughts and heat waves, intensify hurricanes, melt the ice in the Arctic, and raise sea levels.

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Tour de France riders zoom through a field of wheat