When people talk about the most serious effects of climate change, they typically mention hotter temperatures, severe storms, rising sea levels, economic instability, and food security. Typically, the latter threat is measured in terms of the amount of calories produced by world agriculture, to quantify projected changes in maize, soy, wheat, and rice production under new climate conditions. But in a new editorial for Nature Climate Change, CI fellow Joshua Elliott and two co-authors explain how new research on changes in nutritional value of food grown in high-CO2 conditions suggests that calories alone may insufficiently describe the food security threat.
Because carbon dioxide promotes plant growth and photosynthesis, some scientists believe that increased atmospheric CO2 may have both positive and negative effects on agriculture. While temperature and water supply changes would be expected to negatively affect crops, higher CO2 could counteract some of that damage by boosting plant fertilization. But a new study in Nature by researchers from Harvard and several other institutions finds that plants grown in high-CO2 conditions contain reduced amounts of zinc, iron, and protein. As Elliott, a research scientist at the Center for Robust Decision Making on Climate and Energy Policy (RDCEP), and his co-authors write, "This leads to the possibility that assessments that focus on food quantity could be comparing apples to oranges. In other words, even if CO2 fertilization has the potential to compensate much of the negative climate change effects on agricultural yield, nutritional value may nevertheless be compromised."
A subsequent analysis using global gridded crop models from the Inter-Sectoral Impact Model Intercomparison Project (ISI-MIP) found that increasing carbon dioxide scenarios produce significantly lower world supplies of iron, zinc, and protein -- a particular issue for the billions of people around the world that already struggle with "hidden hunger" -- scarce supplies of nutrition-rich food.
As long as food commodities are priced by weight or volume and only rough categories are used to distinguish quality (for example, the use of protein content to determine baking quality in wheat), a decrease in essential minerals will go largely unnoticed by consumers and effectively increase the prices of nutrients essential to human nutrition.
Elliott and colleages conclude that current crop models must be improved to represent these more complex effects of climate on the nutritional content of staple crops, as well as expanded to include other crops such as legumes and grains that may be more important in the future of agriculture under climate change.