From the Los Angeles Times
Ozone hampering plants' absorption of carbon dioxide
Pollution seems to limit the ability of flora to offset
greenhouse gases.
By Amber Dance
Times Staff Writer
July 26,
2007
Rising levels of ozone pollution near the ground are damaging the
ability of plants to take up carbon dioxide, reducing their potential to act as
a counterbalance to greenhouse gas accumulation, scientists said
Wednesday.
When affected by projected high levels of ozone, plants can
absorb up to one-third less carbon dioxide than healthy plants, the researchers
found.
The finding adds a new component that will have to be factored
into climate models used to assess the future effects of global warming, they
said.
The study, published online by the journal Nature, was the first to
consider the indirect effect of ozone on vegetation.
"It points out a
real gap in our knowledge of climate change," said David Karnosky, a global
change scientist at Michigan Technological University who was not associated
with the study.
Ozone forms when nitrogen oxides and volatile
hydrocarbons meet in the presence of sunlight. The precursors to ozone come
primarily from the burning of fossil fuels, although plants also emit carbon
compounds that can participate in the reaction.
High in the stratosphere,
ozone is beneficial, shielding Earth from harmful radiation. In the lower
atmosphere, it functions as a greenhouse gas and is an air pollutant that can
make it hard for people to breathe.
Ozone pollution is particularly high
downwind of industrial areas across the eastern United States, Southern
California and parts of Texas.
The gas attacks plants by breaking down
their cells, reducing growth and causing premature aging.
While the U.S.
has been trying to limit nitrogen oxide emissions, ozone levels are creeping
upward because of continued burning of fossil fuels.
In some areas of the
world, ozone levels are above 40 parts per billion. Some computer models project
that 40 parts per billion will be the global norm by 2100 and that levels will
exceed 70 parts per billion in some areas, according to the study.
The
researchers, led by Stephen Sitch, a climate scientist at the Met Office Hadley
Center for Climate Change in Britain, used computer models to analyze how plant
life would respond to increasing levels of carbon dioxide and
ozone.
Sitch and his colleagues projected that the largest reduction in
carbon absorption would take place over North America, Europe, China and
India.
"In those areas where ozone is a very large driver, the capability
of those trees planted to sequester carbon is going to be limited," Karnosky
said.
The scientists have not calculated how the ozone factor will affect
temperature predictions.
--
amber.dance@latimes.com
