Scientists have developed a way to use corn plants to monitor and map the human-generated emissions of carbon dioxide.
Only a small fraction of Earth's atmosphere is carbon dioxide. In summer 2004, that share averaged about 378 parts per million (ppm), says James T. Randerson, a biogeochemist at the University of California, Irvine. Within that component, about one in a trillion of the carbon atoms is carbon-14 (C-14), a radioactive isotope produced by cosmic rays at high altitudes.
However, the carbon dioxide produced by burning fossil fuels has no C-14. That's because the isotope decays to undetectable concentrations after about 50,000 years, and fossil fuels derive from organic material much older than that. By measuring the proportion of C-14 in corn plants, Randerson and his colleagues can determine the mix of naturally occurring and fossil fuel–generated carbon dioxide that the plants absorbed as they grew.