Crop Nutrient Decrease from CO2 Concentration—Graph : Climate Interactive

Big messages:

The graph shows the average reductions in three key dietary nutrients (protein, iron and zinc) across four major staple crops.
In laboratory experiments, crops grown under higher atmospheric CO₂ concentrations show lower levels of these nutrients, providing strong evidence that rising CO₂ can reduce crop nutritional quality.
Dietary deficiencies of these key nutrients are already a major global public health problem. Worldwide, over half of children under the age of five are deficient in iron, zinc, or vitamin A. Inadequate nutrient levels can lead to stunted growth, higher susceptibility to disease, and anemia (Our World in Data).
Wheat, rice, soybeans, and maize are significant sources of these nutrients in people's diets, so a reduction in nutrient content threatens human health. Wheat, for example, contributes about 20% of total protein in human diets globally, reaching nearly 40% in some regions, such as northern Africa and the Middle East (Erenstein et al., 2022). Around 2.3 billion people live in countries in which 60% of dietary zinc or iron comes from grains and legumes such as soybeans (Myers et al., 2014).
Reducing CO₂ emissions is crucial to prevent a higher atmospheric CO₂ concentration from harming human nutrition and health.

Increasing risk. These three nutrients have already decreased by 1-2% from their 1995 levels in crops, and a rising atmospheric CO₂ concentration is expected to cause an even greater decline by 2100.
Double threat. The risk of this impact is multiplied by the decrease in crop yields shown in the “Crop Yield Decrease from Warming” graph. Lower yields combined with lower nutrient content in key crops can pose a major threat to food security in the future.
Delayed response to action. Due to delays in the energy and climate systems, climate policies implemented today will only begin to show noticeable impact on CO₂ concentration, and therefore on crop nutrients, in the 2040s.
Hope for a better future. Reducing CO₂ concentration below today’s level could lead to an increase in crop nutrient content compared to today. To reduce atmospheric CO₂ concentration, CO₂ emissions need to be lower than CO₂ removals. The metaphor of a bathtub helps explain this system dynamic of the climate. Read more in the En-ROADS Dynamics section of the En-ROADS User Guide.

Pair this graph with the "Crop Yield Decrease from Warming" graph to highlight the compounding risk of these two impacts.
Unlike most other climate impacts shown in En-ROADS, crop nutrient decline—like ocean acidification—is driven by rising CO₂ levels in the atmosphere rather than temperature.
The research behind this graph (Myers et al., 2014) focused on three key nutrients: protein, iron, and zinc. Protein is a macronutrient, while iron and zinc are micronutrients. Macronutrients, like protein, fat, and carbohydrates, are nutrients we need in larger amounts for energy. Micronutrients, such as vitamins and minerals, are also important but required in much smaller amounts. For simplicity, this graph shows the average decrease across all three nutrients in this study, as deficiencies in any of them can seriously impact health.
Maize is less affected by increasing CO₂ concentrations than the other crops shown in this graph. Research suggests that this is due to differences in their photosynthesis process. Most plants, including wheat, rice, and soybeans, use C3 photosynthesis, where the first carbon compound formed contains three carbon atoms. In contrast, maize relies on C4 photosynthesis, which produces a four-carbon compound and is more common in hot, dry environments. C4 plants like maize appear to be less sensitive to increased CO₂ concentrations.

Food and nutrition security are more widespread problems in lower-income regions of the world, making these regions especially vulnerable to worsening conditions (Global Nutrition Report, 2022).
People in lower-income regions often rely more on plant-based diets, putting them at greater risk from the effects of reduced crop nutrients (Our World in Data, 2023).
Efforts to mitigate climate change may also negatively affect food security. For example, a carbon tax is likely to increase prices of agricultural products and food in both direct and indirect ways. The negative impacts would be most prevalent in vulnerable, low-income regions such as Sub-Saharan Africa and South Asia. Such impacts are not modelled in En-ROADS, but need to be monitored when implementing policies in the real world.