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Some other news, scientists are reporting that some of the world's most important crops contain fewer crucial nutrients when they grow in an environment with high levels of carbon dioxide. That is awkward because the concentration of this greenhouse gas in the air is rising. This could make the problem of malnutrition even more difficult to solve. NPR's Dan Charles reports.

DAN CHARLES, BYLINE: Scientists have been trying to get an idea how crops will grow when there's more carbon dioxide in the air. In various parts of the world they've been doing experiments with rice, wheat, peas and other crops. Samuel Myers, a researcher at Harvard's School of Public Health, says these are open air experiments.

SAMUEL MYERS: Except that in the field are placed rings of carbon dioxide-emitting jets.

CHARLES: And those jets release just enough carbon dioxide to simulate the atmosphere that crops will almost certainly experience 40 or 60 years from now. They've found crops do grow faster when there's more carbon dioxide. They often produce harvests that are 10 percent bigger. That sounds like a good thing, but Samuel Myers and his colleagues took a closer look, examining not just the quantity of the harvest but also the quality.

MYERS: What we found were five to 10 percent reductions in nutrients like iron, zinc, and protein.

CHARLES: Myers is not sure what's causing this. One theory is when a plant produces more grain or beans, the trace nutrients get diluted. No matter what the cause, the effects could be really significant, he says, and harmful. About two billion people around the world already are getting too little iron and zinc in their diets, and it's damaging their health.

MYERS: Some zinc deficiencies, you see increased child mortality because their immune systems don't work and iron deficiency causes increases in maternal mortality, reductions in IQ.

CHARLES: So if some of the world's most important crops provide even lower levels of these nutrients in a future high-CO2 world, Myer says it's likely to make the problem even worse. Iron and zinc deficiencies have gotten a lot of attention in recent years. The best solution would be finding ways for people to eat a wider range of foods, because some of the world's biggest crops, like rice or corn, don't supply much iron or zinc at all.

But many people rely on those crops because they can't afford anything else. There's also an international effort called HarvestPlus that's breeding new crop varieties that contain higher levels of these nutrients. There's high zinc rice and wheat, for instance. But Michael Grusak, a researcher with the US Department of Agriculture's Children's Nutrition Research Center in Houston says it's proven really difficult to boost the levels of nutrients, like iron, in certain crops.

MICHAEL GRUSAK: And if elevated CO2 or other climate change-related processes are working against us, we're going to have to work even harder to raise these levels.

CHARLES: The new research appears in this week's issue of the journal Nature. Dan Charles, NPR News.

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