OZONE smogs will engulf much of the Earth during the 21st century, triggering
asthma epidemics and damaging crops and forests, say atmospheric chemists.
The prediction is buried in the latest report from the UN鈥檚 Intergovernmental
Panel on Climate Change (IPCC), agreed at a meeting in Shanghai, China, last
week. It warns that by 2100, background levels of the gas could triple until air
quality in most of the northern hemisphere exceeds existing safety standards
designed to protect human health. Behind the rise are soaring emissions,
particularly in Asia, of nitrogen oxides and volatile organic compounds, the
chemicals that react in sunlight to make ozone. No longer localised, ozone smogs
will occur 鈥渙n a hemispheric scale鈥�, the report says.
Dick Derwent, an atmospheric chemist at Britain鈥檚 Meteorological Office in
Bracknell, and an author of the IPCC report, says: 鈥淭he background levels will
be as high as some of today鈥檚 city smogs.鈥� But the effect will not be confined
to cities.
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The IPCC predicts that ozone levels will rise from current background levels
of around 25 parts per billion to 60 ppb by 2060 and more than 70 ppb by 2100.
鈥淚t may be impossible to achieve a clean-air standard of 80 ppb over most
populated regions,鈥� the report says.
Above 30 ppb, concentrations of the gas will damage trees and make crops such
as wheat wilt, according to the European Environment Agency. Above 80 ppb,
hospital admissions for asthma attacks soar.
At lower levels in the atmosphere, ozone acts as a greenhouse gas. So the
extra ozone will accelerate global warming, says Stuart Penkett of the
University of East Anglia. He says that damage to vegetation may be so
widespread that 鈥渋t could alter the Earth鈥檚 reflectivity, at least in the
northern hemisphere, and maybe influence the hydrological cycle鈥�. Both could
further harm the world鈥檚 climate.