Carbon Dioxide Affects More Than Climate

Carbon dioxide's popular reputation has already been sullied as rising levels of the gas contribute to global climate change. But scientists are regularly discovering other ways in which increased carbon dioxide concentrations might impact the world.

Just this week, the National Science Foundation (NSF) published a study showing that high carbon dioxide levels in the past led to increasingly voracious insect populations and noticeably greater damage to plants and trees.

NSF researchers reached that conclusion after examining plant fossils from the Paleocene-Eocene Thermal Maximum (PETM), a period of higher-than-normal temperatures and atmospheric carbon dioxide levels that occurred about 55 million years ago. Fossil plants from the PETM showed greater damage than plants from either before or after that period, which lasted about 100,000 years.

"We wanted to see whether the increase in insect damage during the PETM was because the leaves were less tough or more nutritious," said Ellen Currano, the study's lead author and a researcher with Pennsylvania State University and the Smithsonian Institution. "There is no evidence to support this. Instead, we think that the warming allowed insect species from the tropics, particularly those that feed in a highly specific manner, to migrate north."

A growing body of evidence also indicates that plants grown in higher-than-normal concentrations of carbon dioxide are less nutritious than those grown in normal conditions.

Last month, Max Taub, a biologist at Southwestern University released an analysis that found elevated carbon dioxide levels caused many food crops to drop significantly in protein content. Barley took the greatest hit -- a 15.3 percent decline -- while potatoes (14 percent), rice (9.9 percent) and wheat (9.8 percent) also showed drops in protein levels. Soybeans appeared more adaptable to rising carbon dioxide concentrations, showing a protein decline of just 1.4 percent.

Those findings suggest the world's poor, who depend most on plant sources for their protein, could suffer as the climate continues to warm.

"This is just one more example of the impact global changes could have on us," Taub said.

Other recent discoveries showing how rising carbon dioxide levels might affect the planet's natural systems include:

Research from Met the Office Hadley Center, the University of Exeter and the Center for Ecology & Hydrology indicates plants draw less water from the soil when carbon dioxide levels are high, meaning more water might flow into rivers;

Research from the Plymouth Marine Laboratory that raises concerns about how carbon dioxide might affect the oceans' microbial life, which forms the bottom of the marine food chain;

And research from Michigan Technological University finding that increased carbon dioxide levels is causing trees to see a longer growing season, an impact that could benefit the forestry industry.

The burning of fossil fuels has caused atmospheric carbon dioxide levels to increase from about 280 parts per million (ppm) at the start of the Industrial Age to 380 ppm today. Those levels are expected to continue rising, leading to even warmer average temperatures and other impacts around the globe.