Around the world, food security is being threatened by man-made carbon dioxide (CO2) emissions. Some of the threats to our food system are relatively clear: warmer temperatures and changing climates bring about droughts, heat waves, sea level rise and more frequent and intense extreme weather events —all of which can disrupt food production.
But hidden in the biochemistry of the crops themselves lies another major threat to our public health and food supply. As CO2 concentrations rise, the levels of some key nutrients in staple food crops are lowered. In other words, by emitting historically high levels of carbon pollution, we are literally making our food less nutritious.
Food crops grown at higher carbon dioxide levels have lower amounts of protein, zinc, and iron, all of which are essential nutrients for human health. Specifically, on average, food grown at CO2 levels expected by 2050 will contain 10 percent less protein, 6 percent less iron, and 7 percent less zinc.
This is particularly concerning as over 2 billion people worldwide are already thought to be deficient in one or more of these nutrients with very significant consequences for their health.
Our new research, published in Nature Climate Change, puts the massive scale of these nutrient deficiencies into stark perspective. We found that, as concentrations of CO2 approach 550 parts per million by midcentury, hundreds of millions of people are likely to become newly susceptible to chronic deficiencies of protein and zinc. And billions more are likely to suffer from a worsening of their existing nutrient deficiencies.
In the most tragic of ironies, the poorest, who have been least responsible for elevating CO2 levels, will be most vulnerable to these nutrient losses because their diets are less diverse and generally contain lower levels of iron, zinc, and protein.
Just how bad could it be for the most vulnerable populations? By 2050, we estimate that nearly 2 percent of the global population, or 175 million people, could be pushed by anthropogenic CO2 emissions into zinc deficiency. That’s on top of 1.5 billion who are already deficient in zinc intake. Another 122 million (or 1.3 percent) would join the 662 million who are already protein deficient. And while it’s more complicated to project iron deficiencies, we found that nearly 1.4 billion highly vulnerable people — children under the age of 5 and women of childbearing age — will live in regions that we identified as having the highest risk.
What do these numbers mean? They mean more children dying of pneumonia, malaria, diarrhea, and other infections as their immune systems are compromised by lack of zinc. They mean more women dying in childbirth and infants failing to survive because of iron deficiency. They mean reduced IQs and chronic stunting and wasting in children, and reduced work capacity in adults.
The most vulnerable people are those who are consuming simple, plant-based diets. Specifically, the populations of Africa, Southeast Asia, and the Middle East are most vulnerable to CO2-driven nutrient losses. But the impacts of nutrient loss would be felt all over the world, even in the United States, where core crops like wheat and rice would deliver less nutrition per calorie after being processed into bread, pasta, cereals, and other products that wind up in cabinets and on kitchen tables.
Some critics may argue that CO2 is “plant food” and claim the loss in nutrients will be balanced out by increased crop production. This works in theory — a phenomenon often referred to as CO2 fertilization — but not in reality. This small anticipated increase is more than offset by the very real impacts of climate change, which are already disrupting systems of food production and lowering crop yields, through changes in temperature, soil moisture, and extreme weather events.
Additionally, even if a population were able to increase caloric intake enough to offset CO2-driven nutrient losses, the change in the ratio of calories-to-nutrients consumed would ensure new health problems including obesity and metabolic diseases.
This isn’t to say that all hope is lost. We hope that our research will be used by countries to better prepare for what could be a dangerous drop in nutrition from their typical diets. Governments can and should monitor their crops over time to track nutrient levels as CO2 emissions increase. Beyond that, there’s potential for encouraging dietary diversification or the use of different cultivars of certain crops — such as rice and legumes — some of which have shown different sensitivities to elevated CO2. Focusing on these more nutrient-resilient cultivars could help lessen the health risks to local populations, as could bio-fortification of crops with added nutrients and the simple (but expensive) deployment of nutrient supplementation programs for particularly vulnerable populations.
Stepping up research in each of these areas is imperative for governments around the world, particularly those with the highest carbon footprints who have been most responsible for creating this new public health threat.
Of course, the best and most certain way to ensure the healthiest and most nutrient-rich crops, and to protect the most vulnerable populations, is to rapidly reduce CO2 emissions from human activity.
Samuel S. Myers, MD, MPH, is a principal research Scientist at the Harvard TH Chan School of Public Health and the director of the Planetary Health Alliance. His research focuses on the many ways that human-caused changes to the natural environment impact human health — a field called planetary health.