We are undoubtedly pumping ever more carbon dioxide into the air. But did you know that this is also silently injecting extra carbs into bread, cereals and salad, while the protein and minerals in your food take a hit.
This nutritional cost of changing Earth’s atmosphere is now worrying the world’s most powerful nation. For the first time it is a key finding in an official report on health impacts of climate change in the US, unveiled by the White House today.
Why would more CO2 mean poorer food? Photosynthetic organisms, such as plants, are the carbohydrate factories of the world. They convert CO2 and water into gigatonnes of starch and sugars every year. And every year, since the dawn of the industrial age, humans have been steadily feeding them more and more CO2.
Plants respond by building more carbohydrates but less protein into their tissues. The result is a higher ratio of carbohydrate to protein in most plants, including major crops such as wheat, rice and potato.
This is a double whammy: protein deficiencies afflict much of the developing world, while excess carbohydrate consumption is a worry in obesity-riven developed world.
This is not the only nutritional impact though. To capture CO2 plants open the pores in their leaves. The stomata let in CO2 but allow water to escape: plants compensate by sucking moisture from the soil with their roots. Transpiration, as this water movement is called, is a major hydrological force on Earth. It moves several minerals essential for life, such as calcium and magnesium, closer to the roots, nourishing plants and ultimately us. But plants respond to high CO2 by partially closing stomata and losing less water. This reduces the flow of nutrients to roots and into plants. Less minerals but more carbs creates a higher carbs-to-minerals ratio in crops and on our plates.
In an elevated CO2 world, every serving of bread, pasta, fruits and vegetables delivers more starch and sugar but less calcium, magnesium, potassium, zinc, protein and other essential nutrients. A small nutritional hit in one serving is not worrying, but it can contribute to weight gain when sustained over a lifetime of thousands of servings.
No free lunch
Hidden hunger is a widespread nutritional disorder stemming from diets rich in calories but poor in vital nutrients. It was mainly a worry for the developing world. But back in 2002, New Scientist predicted that “elevated CO2 levels threaten to bring the hidden-hunger problem to Europe and North America”. Scepticism made it difficult to secure funding for testing it and slowed progress on this issue by a decade.
However, the accumulated research evidence has now converged on an unequivocal conclusion: rising CO2 depletes protein and minerals in most foods that underpin human nutrition. This shift in plant quality is systemic through out tissues and pervasive across the world.
Sceptics like to claim that rising CO2 is a boon to humanity, because it boosts crop yields. However, “elevated CO2 could be junk food for a number of plant species,” says a USDA scientist, Lewis Ziska. There is no such thing as a free lunch with climate change: increase in crop quantity serves up a sustained drop in quality.