Crops becoming less nutritious due to rise of CO₂ levels

The nutritional quality of staple foods is declining as rising atmospheric carbon dioxide alters plant biology, with potentially far-reaching consequences for global health and food systems. Research synthesized by scientists at Leiden University shows that crops such as wheat, rice, beans, and chickpeas now contain fewer essential nutrients than they did several decades ago, a trend expected to continue through 2040 and beyond.

A typical meal of chickpeas and rice, for example, provided roughly 22% of daily zinc requirements in the late 1980s but now delivers closer to 20%, with projections suggesting a decline to around 17% by 2040. While the changes appear incremental, scientists warn that even small reductions in nutrient density could significantly increase the prevalence of “hidden hunger,” particularly in regions heavily dependent on plant-based staples.

The “carbon dilution” effect

Scientists attribute much of this decline to what is known as the “dilution effect.” Elevated CO₂ concentrations stimulate photosynthesis, increasing carbohydrate production in plants. However, this accelerated growth is not matched by a proportional uptake of minerals such as zinc, iron, and magnesium.

As a result, crops may grow larger and yield more biomass, but their nutritional value per serving declines. “The diets we eat today have less nutritional density than those of previous generations,” said Kristie Ebi, highlighting the systemic nature of the shift.

Plant physiology under rising CO₂

Higher CO₂ concentrations also affect plant water use. Crops absorb carbon dioxide through microscopic leaf pores known as stomata. When CO₂ levels rise, plants partially close these pores, reducing water loss—but also limiting the uptake of waterborne nutrients from the soil.

According to Lewis Ziska, this increased efficiency comes at a nutritional cost. Reduced water flow through plants leads to lower transport of dissolved minerals, compounding the dilution effect.

Additional climate-related factors further complicate nutrient uptake. Warmer soils can alter microbial activity, reducing nitrogen availability, while increased temperatures may raise concentrations of harmful substances such as arsenic in crops like rice.

Health risks and global exposure

The decline in nutrient density is expected to exacerbate existing deficiencies worldwide. Estimates suggest that by mid-century:

• An additional 175 million people could become zinc-deficient
• 122 million more may face protein deficiency
• Up to 1.4 billion women and children could experience worsening iron intake

According to World Health Organization, between 30% and more than half of the global population already suffers from inadequate micronutrient intake.

Iron deficiency, in particular, poses severe risks. In countries such as Nigeria, anemia among women of reproductive age contributes to complications during childbirth, including increased mortality risk.

Limited mitigation options

While high-income countries may offset nutrient losses through dietary diversification, supplementation, and fortified foods, lower-income regions face structural constraints. Diets in these areas often rely heavily on a narrow set of staples, limiting the ability to compensate for declining nutrient content.

Policy interventions such as food fortification and crop diversification have shown partial success but remain insufficient to counteract ongoing nutrient dilution. Research also suggests that agricultural policies emphasizing high-yield crops over nutrient-rich varieties may worsen the problem.

Outlook for agriculture and food systems

Experts emphasize that reducing greenhouse gas emissions remains the most effective long-term solution. While elevated CO₂ can enhance plant growth, its broader impacts—including nutrient dilution, extreme weather, and declining yields—are expected to outweigh any benefits.

Without intervention, the combination of lower nutrient density and climate-related yield losses could significantly strain global food systems, particularly in vulnerable regions.

Source: The Washington Post