A recent story on NPR reviewed a new body of emerging research on the nutritional impact on food crops of the higher carbon dioxide levels in the atmosphere that are the driving force of global climate change.
Atmospheric CO2 levels are up and continuing to rise, and scientists are working to understand how this will effect plant life, and agriculture in particular. To test the effects of this changing atmosphere, researchers are growing important food crops in controlled conditions with varying levels of CO2. Results generally show the same pattern– as carbon dioxide goes up, nutritional quality goes down.
However, higher CO2 growing conditions do not affect all plants in the same way. An international group of researchers (Zhu et al., 2018) found that, for example, high CO2 rice was lower in protein, iron, zinc and B vitamins (decreased by 10, 8, 5, and 12-30 percent respectively). But, earlier research by a team at Harvard found that carbon dioxide levels similar to what we expect to see 40 to 60 years from now showed a 5-10% reduction in iron, zinc and protein in crops like wheat, soybeans, and field peas, while maize and sorghum were less affected (Myers et al., 2014).
Scientists are unsure of the answer to both why this happens and what impact it will have on human health.
One theory as to the mechanism is that plants grown in high CO2 are, as one researcher puts it, “carbon-rich but nutrient poor” (Kennedy, 2018). An environment rich in carbon dioxide does seem to result in vigorous growth — plants are generally larger in size and the Myers et al. study (2014) found that yields were around 10% higher in their experimental plots.
So, this could be a simple dilution effect – same amount of nutrients spread across more plant tissue. But, this theory doesn’t quite hold water, high CO2 appears to only impact some types of nutrients and reductions are not seen across all nutritional measures.
The human health impacts are also an unknown. Given what we already know about the poor quality of the modern American diet, we can’t help but feel that less nutrition in many staple crops could have a more significant impact than we think.
After all, rice is a central part of the diet for over 2 billion people worldwide, many of them in developing nations where other options could be limited. If the rice they eat is 5-30% less nutritious, there will be health impacts. Given the seemingly unstoppable runaway train of climate change, we are pretty likely to find out just what those may be.
Merritt Kennedy, “As Carbon Dioxide Levels Rise, Major Crops Are Losing Nutrients,” NPR, June 19, 2018.
Samuel S. Myers, Antonella Zanobetti, Itai Kloog, Peter Huybers, Andrew D. B. Leakey, Arnold J. Bloom, Eli Carlisle, Lee H. Dietterich, Glenn Fitzgerald, Toshihiro Hasegawa, N. Michele Holbrook, Randall L. Nelson, Michael J. Ottman, Victor Raboy, Hidemitsu Sakai, Karla A. Sartor, Joel Schwartz, Saman Seneweera, Michael Tausz & Yasuhiro Usui, “Increasing CO2 threatens human nutrition,” Nature, 2014, 510, DOI: 10.1038/sdata.2015.36.
Chunwu Zhu, Kazuhiko Kobayashi, Irakli Loladze, Jianguo Zhu, Qian Jiang, Xi Xu, Gang Liu, Saman Seneweera, Kristie L. Ebi, Adam Drewnowski, Naomi K. Fukagawa and Lewis H. Ziska, “Carbon dioxide (CO2) levels this century will alter the protein, micronutrients, and vitamin content of rice grains with potential health consequences for the poorest rice-dependent countries,” Science Advances, 2018, 4:5, DOI: 10.1126/sciadv.aaq1012.