Ozone Counteracts Some Benefits of Carbon Dioxide in Forests

Summary

Results of a long-term field study funded by the U.S. Department of Energy’s (DOE’s) Office of Science, and published this week in the international scientific journal Nature, indicate that global carbon cycle models must in the future consider the potentially negative biological and ecological effects of rising tropospheric ozone concentrations not just the biological benefits of rising carbon dioxide concentrations when predicting the future global carbon cycle and climate. Although ozone and carbon dioxide are added to the atmosphere by several natural processes, fossil fuel use along with other human activities are increasing the concentrations of both gases in the lower atmosphere. Ozone and carbon dioxide can each affect fundamental processes occurring within the terrestrial biosphere; they can also affect the climate system. In their Nature article, the authors reported that benefits of elevated carbon dioxide concentrations on carbon addition to, and storage in, forest soils were reduced or eliminated by a concomitant increase in ozone concentration. When ozone concentration was elevated (at a unique DOE field experimental facility in northern Wisconsin) to reflect a possible future atmospheric composition, incorporation of carbon into soil under forest stands treated with elevated carbon dioxide for four years was reduced by about 50%. These results call into question existing global carbon cycle models–some of which are coupled to climate models and serve as tools to estimate future climatic variability and change–that assume that the well-documented rising global atmospheric carbon dioxide concentration will result in significant additional carbon storage in forest soils.