Rising CO2 levels may boost crop calories but reduce nutrients, study finds

Higher levels of carbon dioxide (CO2) in the atmosphere may be making food more calorific but less nutritious, and could also increase toxic elements in crops, according to a new study by researchers at Leiden University in the Netherlands.

The research, led by Sterre ter Haar, a lecturer at Leiden University, developed a method to compare results from multiple studies examining how plants respond to rising CO2 levels. The analysis found that while elevated CO2 can increase crop yields, it is associated with a decline in nutrient density. Zinc levels were found to drop significantly in several crops, while lead levels increased.

Ter Haar said the findings challenged the assumption that nutrient losses were due only to a “dilution effect” caused by faster plant growth. The study suggests a broader change in the composition of food crops as CO2 levels rise.

Scientists have studied the impact of atmospheric CO2 on plants for more than a decade, but differences in experimental conditions have made comparisons difficult. The Leiden team addressed this by establishing a baseline CO2 concentration of 350 parts per million (ppm), often described as the last “safe” level, and comparing it with 550 ppm — a level some projections suggest could be reached by around 2065.

Using this approach, the researchers analysed almost 60,000 measurements across 32 nutrients and 43 crops, including rice, wheat, potatoes and tomatoes. They found that most nutrients showed a negative response to higher CO2 levels, with an average decline of 3.2 per cent.

The impact was more pronounced in some cases. Zinc levels in chickpeas were projected to fall by up to 37.5 per cent, while essential crops such as rice and wheat showed significant reductions in protein, zinc and iron. The researchers warned this could contribute to “hidden hunger”, where people consume enough calories but insufficient nutrients.

The study noted that current atmospheric CO2 levels have already reached about 425 ppm, which it said has likely begun to affect plant nutrition.

Other scientists said the findings provided a useful basis for further research. Courtney Leisner of Virginia Tech said the study highlighted how environmental conditions influence crop nutritional quality, an issue central to future food security.

However, Jan Verhagen of Wageningen University said factors such as fertiliser use and farming practices also play a major role, and more research would be needed to isolate the effects of CO2 alone.