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More carbon dioxide in the environment is making food more calorific but less nutritious – and also potentially more toxic, a study has found.
Sterre ter Haar, a lecturer at Leiden University in the Netherlands, and other researchers at the institution created a method to compare multiple studies on plants’ responses to increased CO2 levels. The results, she said, were a shock: although crop yields increase, they become less nutrient-dense. While zinc levels in particular drop, lead levels increase.
“Seeing how dramatic some of the nutritional changes were, and how this differed across plants, was a big surprise,” she told the Guardian. “We aren’t seeing a simple dilution effect but rather a complete shift in the composition of our foods … This also raises the question of whether we should adjust our diets in some way, or how we grow or produce our food.”
While scientists have been looking at the effects of more CO2 in the atmosphere on plants for a decade, their work has been difficult to compare. The new research established a baseline measurement derived from the observation that the gas appears to have a linear effect on growth, meaning that if the CO2 level doubles, so does the effect on nutrients. This made it possible to compare almost 60,000 measurements across 32 nutrients and 43 crops, including rice, potatoes, tomatoes and wheat.
“Although there was a lot of data from previous studies, there were few answers,” said Ter Haar. “These studies used paired experiments, where plants were grown under identical conditions except for one thing: the CO2 level. This gives insight into possible changes, but the sample sizes were usually too small to draw conclusions from. Comparing these individual studies with each other was difficult because, as we know, the baseline of CO2 is continuously increasing in our atmosphere, meaning that the baseline in these experiments is also increasing.”
Their “baseline” measurement was a gas concentration of 350 parts per million – sometimes referred to as the last “safe” level. They compared this with a concentration of 550 parts per million, which some scientists expect to be reached by 2065. Most nutrients would respond negatively to the rise in concentration, they said, with an average drop of 3.2%.
However, zinc in chickpeas would be expected to plummet by up to 37.5%, with a “significant” decrease in protein, zinc and iron in essential crops such as rice and wheat. The researchers warned of “devastating health consequences” including “hidden hunger, where people have sufficient food calorically but insufficient nutrients”.
The CO2 level is now 425.2 parts per million, the paper said, which had already resulted in “lowered levels of plant nutrition due to CO2 rise”.
The study is part of a growing body of research on the impact of climate breakdown on crops, not only outdoors but also in artificial conditions. The Netherlands is one of the world’s largest agricultural exporters, with three-quarters of its production for export and more than 4,100 hectares of greenhouses, where crops are grown in CO2-enriched environments to increase the yield.
“Climate change isn’t a faraway problem,” said Ter Haar. “The effects are already on our dinner plate.”
Other experts welcomed the Dutch study, saying it was a good basis for further investigation. Courtney Leisner, an assistant professor at the school of plant and environmental sciences at Virginia Tech in the US, coauthored a study earlier this year on how crop improvement strategies could counteract the negative effects of CO2 on crop quality. “This study offers critical insights into how environmental conditions affect crop nutritional quality, which is essential for sustaining future food security,” she said.
There are, however, other factors such as fertiliser application that play an important role in how nutritious our crops are, said Jan Verhagen, a researcher on climate change and sustainable agriculture at Wageningen University.
“Indeed, nutrient levels in plants are changing,” he said. “Whether this is only related to CO2 is, I believe, less clear … we know that nutrition is a key factor in food security and health in general, so it makes sense to shift the focus on this topic.”
He said more experiments would be needed to help design breeding programmes for crops with certain nutrient levels under different environmental stresses to better understand the effects of agricultural practices.
The meta-analysis raises as many questions as it answers, said Ter Haar – who wants to do further study on climate change and nutrients.
“Our goal isn’t to scare people,” she said. “The first step in solving a problem is acknowledging it, and with that, we think our study could be a useful puzzle piece.”
The research was published in the journal Global Change Biology.
