Scientists are seeing a troubling consequence of rising carbon dioxide emissions: a decrease in the nutritional value of staple crops in the global diet.

This drop in crops' key nutrients increases the risk for dietary deficiencies in the world's most vulnerable populations, according to a new study.

Samuel Myers, a senior research scientist in the department of environmental health at Harvard T.H. Chan School of Public Health, studies the effect of human-caused carbon dioxide emissions on crops.

He published a study in 2014 that found elevated levels of carbon dioxide in the atmosphere lower the concentration of key nutrients, including iron, zinc, and protein, in staple food crops like rice, wheat, and soybeans, among others.

Myers' new research focuses on quantifying the potential real-world health effects of these findings.

The study, published online in Environmental Health Perspectives, estimates that if carbon dioxide levels continue to rise at their projected levels, the populations of 18 countries may lose more than 5 percent of their dietary protein by 2050. That would place an additional 150 million people at risk of protein deficiency due to elevated carbon dioxide levels in the atmosphere.

Across the globe, about 76 percent of the population gets most of their daily protein from plants. The findings pose the biggest challenges for Sub Saharan Africa, where millions of people are already protein deficient, and South Asian countries, including India, where rice and wheat make up a large portion of daily protein.

"For you and I in North America eating a pretty diverse diet, we're probably getting well above the threshold of iron, zinc and protein in our diet," Myers told CBS News. "But it turns out that there are billions of people in lower income countries who don't have really diverse diets and don't have access to animal sourced food rich in these nutrients and are getting the majority of their iron, zinc, and protein from crops. And many of these people are close to the threshold."

The researchers estimate that India alone will lose 5.3 percent of the total protein in its diet, placing an additional 53 million people at risk for iron deficiency.

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