Plants love carbon dioxide. Higher levels of CO2 in the air increase the rate of photosynthesis—it’s why planting more trees helps to clean the air, after all. For a time, that love had some scientists convinced that the world’s greenery could keep CO2 levels in the atmosphere in check—but research has now shown not only that plants alone can’t halt the rise of CO2 but that the increase will make food crops less healthy for human consumption. According to one new study, higher carbon dioxide levels could turn healthy fruits and veggies into junk food.

According to a report released in early April by the U.S. Global Change Research Program, the level of CO2 we’re predicted to reach by 2100 could result in plants that are high in carbohydrates but low in proteins and important micronutrients. In areas with high levels of food insecurity, this could result in even higher levels of malnutrition and micronutrient deficiencies. In parts of the world that retain a more consistent food supply, people would have to eat considerably more just to get the same levels of nutrition—increasing the prevalence of obesity in the process.

Overall, the report states, “This direct effect of rising CO2 on the nutritional value of crops represents a potential threat to human health.”

The report notes that even today, between 38 and 45 percent of citizens in the prosperous United States “fall below the estimated average requirements for calcium and magnesium, respectively.” Zinc deficiencies may only affect 12 percent of the population at large, but up to 40 percent of elderly Americans have low levels of the nutrient. In addition to lowering overall immunity, diets low in zinc can cause skin sores, slowed growth, and trouble seeing in the dark. Pregnant women, children, and the elderly will continue to be most at risk from the effects of malnutrition and other dietary deficiencies.

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While the report focuses on CO2 levels decades in the future, Lewis Ziska, a plant physiologist for the USDA and one of the report’s lead authors, said CO2 doesn’t increase at a linear rate. “Most of the changes happened in the last couple of decades,” he explained. Though levels of CO2 today are high—potentially the highest in human history—it doesn’t seem to have significantly affected plant nutrients. But that CO2 increases have been happening at higher rates in recent years means the change could happen sooner rather than later.

The relationship between CO2 and the nutritional value of plants is well documented, and the report uses terms like “very likely” and “high confidence” to describe the likelihood of the changes occuring. The USDA is confident enough that the nutritional nosedive will happen that it is now involved in mitigating its effects. Ziska estimated that over 90 percent of plant species will see carb content rise and nutrients and protein decline. Because of different photosynthetic pathways, corn, sorghum, and legumes “won’t lose protein to the same extent,” he said.

Researchers are already hard at work figuring out how to mitigate a potential nutritional wasteland. Rice, one of the most important source of calories for much of the world’s population, is the main test case. Some varieties of rice have 11 percent protein, and other have only 4 percent, Ziska said. Through documenting how these types of rice react to increased levels of CO2, researchers might be able to find and cultivate types that retain their nutritional makeup.

Breeding plants better suited to climate change might prevent the worst-case scenario. But the implications of high CO2 levels transforming our healthiest food into substances only slightly better than a bag of Doritos shouldn’t be ignored. With more than a hint of sarcasm, Ziska said, “Other than the fact that the rising CO2 by itself is likely to result in plants becoming junk food for all living species, it’s no big deal.”