Climate Change Is Quietly Changing the Nutritional Value of Food

A bowl of rice grown in the atmosphere of 2050 will look, taste, and cook exactly like a bowl of rice grown today. It will also carry measurably less protein, less zinc, and less iron, and nobody eating it will be able to tell. That invisibility is precisely what makes this one of the strangest problems in climate science: a slow, silent erosion of nutrition happening inside the food supply of billions of people, discovered not by public health surveys but by agronomists running experiments in open fields pumped full of carbon dioxide.

The scientist most responsible for surfacing this problem is Samuel Myers, who built the case for it as a researcher at Harvard's T.H. Chan School of Public Health and went on to found the Planetary Health Alliance. In 2014, Myers led a team that published a paper in Nature, "Increasing CO2 Threatens Human Nutrition," built on data from Free-Air CO2 Enrichment experiments, open-air plots in the United States, Japan, and Australia where crops are grown under the carbon dioxide levels expected later this century, roughly 550 parts per million, compared with today's roughly 430. The results reshaped how researchers think about the relationship between climate and hunger. Rising CO2 was not just changing where and how much food could be grown. It was changing what the food itself was made of.

The Rice That Feeds Asia Is Quietly Losing Its Protein

Rice is the test case that matters most, because more people depend on it for daily survival than on any other crop. A 2018 study in Science Advances, led by Chunwu Zhu and colleagues in China and reported alongside Myers's Harvard-based research network, grew eighteen genetically diverse rice strains under FACE conditions and found average declines of roughly 10 percent in protein, 8 percent in iron, and 5 percent in zinc, along with double-digit drops in several B vitamins, including a roughly 30 percent fall in folate. Vitamin E was the one nutrient that rose. Everything else that matters nutritionally in a grain of rice went down.

Those numbers sound abstract until you place them against where rice is actually eaten. In Bangladesh, Cambodia, Laos, Vietnam, and Myanmar, rice supplies more than half of daily caloric intake for hundreds of millions of people, and for the poorest households it also supplies a disproportionate share of daily protein and iron. A ten percent decline in protein content is not a rounding error in a diet with few other protein sources. It is the difference between adequate nutrition and a slow deficit that shows up years later as stunted growth in children or as chronic fatigue in adults who never learn the cause.

How More Carbon in the Air Means Less Nutrition in the Grain

The mechanism is not mysterious, and it is not really about pollution in the sense most people imagine. It is about photosynthesis working too well. Rice, wheat, barley, oats, and most legumes and tubers use what's called the C3 photosynthetic pathway, which becomes more efficient as atmospheric CO2 rises. Plants grown in CO2-enriched air produce more carbohydrate, more starch and sugar packed into every grain, at a faster rate than they can pull nitrogen, zinc, and iron out of the soil to match it. The result is a dilution effect: more grain, made of a higher proportion of empty carbohydrate and a lower proportion of protein and minerals.

There is a second, more direct effect layered on top of that. Research led by plant physiologist Arnold Bloom at UC Davis found that elevated CO2 actively interferes with a plant's ability to convert nitrate from the soil into amino acids and protein, independent of any dilution from extra starch. Elevated CO2 also causes plants to partially close their stomata, the pores that drive water uptake, which in turn slows the flow of water carrying dissolved zinc and iron up from the roots. Three separate processes, one shared outcome: less nutrition per calorie, at exactly the moment global calorie production is what most of the agricultural world is optimized to maximize.

Corn and Sorghum Are Mostly Escaping This Fate, and That Divide Matters

Not every crop is vulnerable. Maize, sorghum, millet, and sugarcane use a different photosynthetic pathway, C4, that is already effectively saturated with carbon dioxide at today's atmospheric levels, so raising CO2 further does little to their internal chemistry. This split between C3 and C4 crops draws an uncomfortable map across the developing world. Regions that lean on C3 staples, rice across South and Southeast Asia, wheat across South Asia and North Africa, are exposed. Regions with heavier reliance on C4 staples like maize and sorghum, common across parts of sub-Saharan Africa and Central America, are comparatively insulated from this particular mechanism, though many of those same regions face their own version of the problem through wheat and rice imports, and through separate climate stresses on maize yields and drought.

Two Billion People Are Living Downstream of a Chemistry Experiment

Myers and his Harvard collaborator Matthew Smith turned the FACE data into a global public health forecast in a 2018 paper in Nature Climate Change, "Impact of Anthropogenic CO2 Emissions on Global Human Nutrition." Using dietary data from more than 150 countries, they modeled what happens to a population's effective nutrient intake when the crops it eats quietly lose a few percentage points of protein and zinc. Their central estimate: by 2050, an additional 175 million people could become zinc deficient and 122 million could become protein deficient, purely as a consequence of rising CO2 acting on the crops already in the global food supply, with no change in farming practices, diets, or population assumed.

The paper's most sobering finding was not the aggregate number but its concentration. The burden falls almost entirely on countries that were already nutritionally vulnerable before this effect was ever measured. India, with its enormous population dependent on rice and wheat and its already-high rates of anemia and childhood stunting, emerged as the single largest contributor to projected new zinc deficiency, with researchers estimating tens of millions of additional cases concentrated there alone. Sub-Saharan Africa and parts of Southeast Asia followed close behind.

Zinc Deficiency Is a Child Development Problem Wearing an Agronomy Disguise

Zinc rarely makes headlines the way calories or protein do, but its absence is far from cosmetic. It is essential to immune function, wound healing, and the cell division that drives physical growth in early childhood. Populations with marginal zinc intake, which already includes hundreds of millions of people across South Asia, already carry elevated rates of childhood stunting, diarrheal disease, and susceptibility to respiratory infection. A model published by Smith and Myers's research network is explicit that the projected CO2-driven decline does not need to push anyone from adequate intake to zero. It only needs to push people who were already near the threshold slightly further below it, and at population scale, that threshold effect is what generates tens of millions of new cases.

India's Iron Problem Is Set to Get Worse Before It Gets Better

Iron deficiency and its downstream consequence, anemia, is already one of the most widespread nutritional problems on Earth, concentrated among women of reproductive age and young children. A 2017 GeoHealth study led by Smith, along with Christopher Golden and Myers, estimated that roughly 1.4 billion women and children in countries already at elevated risk of iron deficiency could see their dietary iron intake fall by more than 4 percent as CO2 concentrations rise, with South Asia and parts of the Middle East and North Africa facing the steepest increases in anemia-related disease burden. India carries a disproportionate share of this risk twice over, both because of its existing anemia prevalence, which national health surveys have long ranked among the highest of any major country, and because wheat and rice together make up such a large share of the Indian diet that even a small percentage decline in grain iron content translates into a large absolute reduction in national iron intake.

The Public Health System Built to Catch This Barely Knows It Exists

What makes this threat unusual, and genuinely hard to manage, is that it evades almost every tool public health agencies normally use to track nutrition. Famine monitoring watches calories and crop yields, both of which can rise even as nutrient density falls, since elevated CO2 tends to increase overall biomass and grain yield while degrading its composition. Fortification programs address specific deficiencies but were not designed around a threat that degrades the baseline nutrient content of the staple crops those programs are built on top of. A 2026 review in Frontiers in Plant Science, alongside continuing coverage from outlets including the Johns Hopkins Bloomberg School of Public Health's magazine and Civil Eats, has pushed for breeding programs aimed specifically at nutrient retention under elevated CO2 and for national dietary surveys to begin incorporating projected nutrient decline rather than treating today's crop composition as a fixed baseline.

That policy shift has been slow, and it is running against a clock set by atmospheric chemistry rather than political cycles. The CO2 concentrations used in the original FACE experiments, once treated as a distant midcentury benchmark, are now only a few decades away on current emissions trajectories. The nutritional profile of rice and wheat is not a side effect of climate change waiting to happen. It is already changing, grain by grain, in fields being harvested this year, and the people who will feel it first are the ones with the least room left to absorb another deficit.

Sources: Nature, "Increasing CO2 Threatens Human Nutrition" (Myers et al., 2014); Harvard Gazette / Harvard T.H. Chan School of Public Health, coverage of Samuel Myers's CO2-nutrition research; Science Advances, "Carbon Dioxide (CO2) Levels This Century Will Alter the Protein, Micronutrients, and Vitamin Content of Rice Grains" (Zhu et al., 2018); Nature Climate Change, "Impact of Anthropogenic CO2 Emissions on Global Human Nutrition" (Smith and Myers, 2018); GeoHealth, "Potential Rise in Iron Deficiency Due to Future Anthropogenic Carbon Dioxide Emissions" (Smith, Golden, and Myers, 2017); Johns Hopkins Bloomberg School of Public Health Magazine, "Less Nutritious Crops: Another Result of Rising CO2" (2024); ScienceDirect, "Nutritional Challenges of Staple Crops Due to Increasing Atmospheric Carbon Dioxide Levels: Case of Sub-Saharan Africa" (2024); Frontiers in Plant Science, "Elevated CO2 and the Hidden Hunger Crisis: Mechanisms, Magnitudes, and Mitigation of Micronutrient Dilution in Staple Crops" (2026); Civil Eats, "Why Crops Are Becoming Less Nutritious" (2026); The Washington Post, "Carbon Pollution Is Making Food Less Nutritious and Risking Health of Billions" (2026)