Increasing carbon dioxide is already impacting our world, and its effects will only get worse: rising and acidifying oceans, altered and more intense weather patterns, increased heat and habitat disruption for billions of animals. Nicola Davis at The Guardian reports there’s another major hiccup we need to add to the list. According to new research, rising carbon dioxide levels will sap some of the nutrients from our crops and lead to dietary deficiencies in millions of humans.

In 2014, field trials of common food crops including wheat, rice, corn and soybeans showed that as the amount of carbon dioxide in the atmosphere increased, the levels of iron, zinc and protein decreased in the dietary staples by 3 to 17 percent. While the decrease in a few nutrients may not seem important in food secure countries, it could have a big impact in poorer nations. Nutrient deficiencies are already a major problem faced by about 2 billion people across the globe, impacting the development of infants and children and causing harm to babies in the womb. Currently, 63 million years of life are lost annually due to zinc and iron deficiencies alone.

In the new study in the journal Nature Climate Change, researchers calculated the impact of declining nutrients on human health. According to a press release, the team looked at the impact of rising CO 2 on 225 different types of food. Based on population estimates for 2050 and an expected rise of carbon dioxide from about 400 parts per million today to 550 ppm by mid-century, the team found that the nutrient deficiencies of those already suffering will worsen, and 175 million more people could join the 1.2 billion who are zinc deficient and 122 million people would be added to the 622 million who don’t receive enough protein. About 1.4 billion women of childbearing age and children under 5 could see their iron intake drop by about 4 percent.

“This is another demonstration of how higher CO 2 could affect global health that may not be as well recognized,” co-author Matthew Smith of Harvard T.H. Chan School of Public Health tells Davis at The Guardian. “Continuing to keep up our vigilance around reducing CO 2 emissions becomes all the more important because of this research.”

In an editorial in The Hill, lead author Samuel Myers, also of Harvard, says these deficiencies are just the starting point for much bigger problems.

“What do these numbers mean? They mean more children dying of pneumonia, malaria, diarrhea, and other infections as their immune systems are compromised by lack of zinc. They mean more women dying in childbirth and infants failing to survive because of iron deficiency. They mean reduced IQs and chronic stunting and wasting in children, and reduced work capacity in adults.”

Charli Shield at Deutsche Welle reports that the hardest hit area would be India, where by 2050 the less nutritious food could lead to 50 million more people being zinc deficient, 38 million more protein deficient and 502 million women and children facing iron deficiency.

Researchers aren’t sure exactly why increased CO 2 decreases nutrients. “We still don't really understand why this is happening, but we think it's a lot more complicated than a simple ‘carbohydrate dilution effect,’” Myers tells Shield. “What we do know is that at higher CO 2 food crops become less nutritious.”

Until recently, it was believed that any nutrient loss in crops would be counterbalanced by increased quantity; more CO 2 , it was believed, would boost the growth of plants. But recent experiments have shown that this only works up to a point. Increased temperature begins to negatively effect plant growth, and by some accounts the Earth has already reached this point of diminishing returns. In his editorial, Myers points out that there’s another problem with CO 2 fertilization—if we have to eat more food to get the same amount of nutrients it could lead to other health issues like obesity and metabolic diseases.

Davis reports there are a few possible solutions to the nutrient problem. We could try to breed new, more nutritious crops or crops that can resist nutrient loss. We could try to fortify foods or increase the intake of animal protein, which has much higher levels of zinc, iron or protein. All of those have other consequences or require lots of time and investment. Or we could do the most logical thing and tackle climate change head on by developing policies and plans to reduce greenhouse gas emissions and strategies to limit the impact of the carbon in the air. If it’s not already too late.