Soaring near-surface ozone levels add to global warming

27 July, 2007:

Rising levels of ozone near the Earth’s surface could harm plant production and crop yields even while increasing global warming, British scientists have warned.

While ozone that is present high in the atmosphere – in the stratosphere – helps shield us from the harmful rays of the sun, it can play havoc closer to the ground.

A report published in the Nature journal says that, by 2100, levels of ozone will rise high enough to stunt the overall worldwide growth of plants.

This phenomenon will drive climate change as fewer plants result in a smaller ‘carbon sink’ to mop up the carbon dioxide from the atmosphere. An excess of carbon dioxide will help trap the sun’s heat in the Earth’s atmosphere, adding to global warming.

Researchers from the United Kingdom’s Meteorological Office, the University of Exeter, and the Centre for Ecology and Hydrology said that near-surface ozone has doubled since 1850 because of industrial processes, chemical emissions from cars, and the burning of forests.

Scientists have concluded that the increase in the level of ozone has not received adequate attention in climate models, which could mean that global warming will be even more severe than previously predicted.

Dr Stephen Sitch, a scientist on climate impacts at the Meteorological Office’s Hadley Centre and lead author of the article, said that climate models have largely ignored atmospheric chemistry, but the new research has identified a cause of potentially increased warming with elevated levels of surface ozone that is likely to suppress plant growth.

Though plants and soil are currently helping slow down global warming by storing about a quarter of human carbon dioxide emissions, the new study says this could be hindered by increases in near-surface ozone in future. As a result, more carbon dioxide would remain in the atmosphere, contributing to global warming.

Professor Peter Cox of the University of Exeter, co-author of the study, summed up the findings thus, “We estimate that ozone effects on plants could double the importance of increase in ozone in the lower atmosphere as a driver of climate change. So policies to limit increases in near-surface ozone must be seen as an even higher priority.”