Excess Ozone Chokes Plants, Accelerates Global Warming

The chemical known as ozone may be making a much more significant contribution to global warming than scientists had previously thought, according to a new study published in the journal Nature."Ozone could be twice as important as we previously thought as a driver of climate change," said study co-author Peter Cox.Ozone occurs naturally in the upper atmosphere, but is produced in the lower atmosphere when sunlight strikes industrial pollutants such as carbon dioxide, methane and nitrogen oxides.Scientists have long known that ozone is a greenhouse gas, trapping radiation within the atmosphere and leading to rising global temperatures. But the new study suggests that ozone may have a much more significant climate impact by adversely affecting plants' ability to remove carbon dioxide from the atmosphere.According to the researchers, high concentrations of ozone and carbon dioxide damage plants' ability to engage in photosynthesis. This weakens the plants, causing their stomata (pores in the leaves) to close. In turn, this reduces that amount of carbon dioxide or ozone that the plants are able to absorb.Because of this complex interaction, scientists previously did not know how significant of an effect ozone pollution had on plants' ability to remove carbon dioxide from the atmosphere. To answer the question, researchers designed two computer models to test how plants would be affected by ozone if they had either high or low sensitivity. They then used these models to estimate the predicted effect of ozone on plants' ability to filter out carbon dioxide using projected ozone levels from 1900 to 2100.Under the high-sensitivity model, plants' ability to remove carbon dioxide from the atmosphere was reduced by 23 percent. Even under the low-sensitivity model, it was reduced by 14 percent."Calculations of the efficiency of land ecosystems to take up carbon would be less efficient than we thought previously," Cox said. "The indirect effect is of a similar magnitude, or even larger, than the direct effect. Arguably, we have been looking in the wrong place for the key impacts of ozone."