Higher levels of carbon dioxide in the atmosphere could increase production of crops but reduce their nutritional value, according to scientists at Ohio State University. Peter Curtis, a professor of evolution, ecology, and biology, worked with researchers to analyze the effects of climate change on plant reproduction and collated data from 159 studies conducted over the past two decades. The seed production of rice increased an average of 42 percent with increased CO2 levels, while soybean production increased 20 percent, wheat 15 percent, and corn 5 percent. But there’s a downside: The level of nitrogen, which is important to building protein in animals and humans, fell by an average of 14 percent across most of the plants studied. “Under the rising carbon dioxide scenario, livestock — and humans — would have to increase their intake of plants to compensate for the loss,” Curtis said.