There are two things you want to get from a harvest. First there’s yield, the amount of grains, beans, or fruit you pull from the fields—and that’s where the focus is placed much of the time, both from the farmer’s perspective and in terms of plant breeding and global development conversations. The other, which isn’t so apparent on the farm, is nutrition. A study published this week in Nature suggests that as CO2 levels in the atmosphere increase in the coming decades, yields may increase. But even as farmers have more wheat, rice, and beans to harvest and eat, the nutrition levels in those staple crops—namely, zinc and iron—are going to drop.
Just last year, the world crossed the dubious threshold of 400 parts per million of carbon dioxide in the atmosphere. By using CO2 jets placed around test plots, the study created growing conditions that approximate a future in which those levels creep upward of 500 parts per million. The grains and legumes grown in this environment had anywhere between 5 and 10 percent less iron, zinc, and protein too. The increase in nutritional deficiencies these drops could cause “represents the most significant health threat ever shown to be associated with climate change,” according to a Harvard press release.
In the United States, where iron is something we control in our diets with pricey steaks or supplements and where zinc is barely an active nutritional concern, a drop in these nutrients doesn’t sound all that troubling. But globally, 2 billion people suffer from zinc and iron deficiencies, amounting to the loss of 63 million life-years annually, according to the study, which was led by the Harvard School of Public Health. Zinc deficiency can lead to an increase in infectious diseases because of its effect on the immune system, and anemia caused by low iron levels contributes to 20 percent of maternal deaths, according to the World Health Organization. That’s at current CO2 levels.
In countries that rely on rice, which is naturally low in iron and zinc, as a staple crop instead of wheat, these deficiencies are already more pronounced. But the only potential upside of the study is that the drop in nutrients varied depending on the variety of rice grown in the future-climate test plots. As such, researchers see an opportunity for plant breeders to develop varieties that, like some of the rice cultivars used in the test, will be less sensitive to the increase of CO2, instead of focusing on breeding to increase yields. There are also breeding efforts focused on increasing the nutrient levels in staple crops through selective breeding and genetic modification.