A dinner plate piled high with food from plants might not deliver the same nutrition toward the end of this century as it does today. Climate change could shrink the mineral and protein content of wheat, rice and other staple crops, mounting evidence suggests.
Selenium, a trace element essential for human health, already falls short in diets of one in seven people worldwide. Studies link low selenium with such troubles as weak immune systems and cognitive decline. And in severely selenium-starved spots in China, children’s bones don’t grow to normal size or shape. This vital element could become sparser in soils of major agricultural regions as the climate changes, an international research group announced online February 21 in Proceedings of the National Academy of Sciences.
Likewise, zinc and iron deficiencies could grow as micronutrients dwindle in major crops worldwide, Harvard University colleagues Samuel Myers and Peter Huybers and collaborators warned in a paper published online January 6 in the Annual Review of Public Health. Futuristic field experiments on wheat and other major crops predict that more people will slip into nutritional deficits late in this century because of dips in protein content, Myers reported February 16 at the Climate and Health Meeting held in Atlanta.
“If we’d sat down 10 years ago and tried to think what the effects of anthropogenic carbon dioxide emissions might be on human health, none of us would have anticipated that one effect would be to make our food less nutritious,” Myers said. “But we can’t fundamentally disrupt and reconfigure most of the natural systems around our planet without encountering unintended consequences.”
Figuring out those unintended nutrient consequences isn’t easy. For selenium, scientists have only a rough idea of the element’s global movements. It’s unclear what proportions erode out of rocks or waft onto land from sea, says biogeochemist Lenny Winkel of ETH Zurich and the Swiss aquatic research group Eawag in Dübendorf. She was the principal investigator for the selenium in soils project in the new Proceedings paper. As far as she knows, it presents the first global look at selenium concentrations in soils and what basic factors influence what’s there. This scale, she says, was “a bit bold.”
Starting with more than 33,000 data points from other sources, Winkel and colleagues pieced together a map of selenium concentrations in soils across much of the globe. Climate popped out as one of the more important predictors of selenium content in soil, a link that hadn’t shown up in small studies. Places where climate turns land arid generally have lower selenium, but soil character matters, too. Places with high organic carbon, as in a woodland rich with fallen leaves, as well as places with abundant clay, tend to do better at retaining selenium.
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Soil concentrations of the element selenium, essential for human life, could change by the end of the 21st century, according to computer simulations based on an intermediate scenario for climate change (a scenario that the Intergovernmental Panel on Climate Change labels RCP6.0). The analysis identified what influences soil selenium now — including precipitation and concentrations of organic carbon in soil — and predicted future concentrations based on those influences.
By the end of the century, about two-thirds of heavily cultivated agricultural land would probably lose selenium under an intermediate scenario of climate change, Winkel and colleagues conclude. With a projected average end-century warming of 2.2 degrees Celsius compared with 1986 to 2005, selenium drops in breadbasket regions in the study by an average of 8.7 percent. Only 19 percent of croplands seem likely to gain selenium.
The new map “is worrisome,” says plant physiologist Philip White of the James Hutton Institute in Invergowrie, Scotland. White, who studies agricultural plants,…