With rustic cabins, sailboats bobbing in the mist and brilliant sunsets over sandy beaches, the University of Michigan Biological Station looks, at first glance, like a sleepy summer camp. But the researchers at this Northern Michigan retreat are making waves in the field of global climate change.
The Michigan team began studying the impact of elevated carbon dioxide (CO2) levels on plants in the 1980s. At the time, it was well known that exposing plants to extra CO2 causes them to grow larger. At first, this looked like a potential boon to agriculture. But when the scientists examined the plants more closely, they discovered serious nutritional deficiencies.
For example, crops such as cabbage and broccoli, grown at twice the current level of atmospheric CO2, had 20 percent less nitrogen and protein in their leaves, studies showed. At the biological station’s lakeside laboratory in Pellston, Michigan, Western Michigan University biologist David Karowe was among the first to show how rising CO2 levels could have a dramatic ripple effect across the entire food web.
Karowe says caterpillars that fed on cabbage leaves exposed to high CO2 had to eat 40 percent more food, due to the decreased protein content. Despite their increased intake, however, the insects were 15 percent smaller. More disturbing news came this year. When Loyola University biologist Nancy Tuchman fed high-CO2 leaves to mosquitoes living in a Pellston stream, the insects grew 50 percent slower. That delayed development, in turn, caused the small fish that feed on mosquito larvae to stop growing. "These fish looked like they were starving," says Tuchman. In the future, game fish that prey on these smaller fish also may be affected, Tuchman adds.
The consequences of adding more carbon dioxide to the atmosphere, through industry, automobile exhaust and other human activities, clearly will harm certain natural ecosystems, the Michigan scientists say. But what about humans?
Richard Lindroth, a University of Wisconsin ecology professor, is not ready to make doomsday predictions. As we move higher up the food chain, he says, the effects become less dramatic. Also, certain plants—such as legumes—do not appear to be affected by high CO2 conditions. That means, with enough genetic variation, plants may eventually correct the problem through natural evolution. Meanwhile, the obvious solution is to cut carbon dioxide production, says Lindroth. "Unfortunately, this is a highly charged political issue," he adds. "The only way to control the increased CO2 is to control our consumption of fossil fuels, and that is going to boil down to individual lifestyle choices."