This is a tricky gas: while protecting life on Earth, ozone can be at the same time a slayer. This gas is constantly forming in a natural way from the oxygen in the atmosphere, while on the ground-level ozone has been increasing due to chemicals emitted by the burning of fossil fuels.
The upper atmosphere (stratosphere) ozone forms a planetary screen against the destructive ultraviolet rays
(without it life on Earth would be impossible), but ground-level ozone can be toxic to humans, animals and plants.
Plants absorb ozone and other gases through their stomata (pores), but ozone at certain levels causes cell damage, revealed by brown splotches on the leaves. The photosynthesis rate drops and plants stop growing. Paradoxically, photosynthesis is the phenomenon through which plants absorb carbon dioxide, the main culprit gas for global warming.
Normally, more carbon dioxide would have boosted plant growth and production with the global warming, but not if ozone is present. That's why carbon dioxide will be continuously stored in the atmosphere, further aggravating global warming.
"Previous models have included the beneficial effects to plants, but they haven't included the negative effects," said lead author Stephen Sitch of the U.K. Met Office.
"In effect the cells have been disrupted," Sitch told LiveScience.
"Essentially the photosynthetic apparatus has been damaged."
Such damage will rather induce great economical loss. In some areas, industrial contamination has already raised the ground-level ozone amounts to harmful concentrations and ozone levels are expected to grow in the 21st century.
Moreover, when carbon dioxide level is high, plants close some of their stomata and still get the necessary amount for photosynthesis. The closures also stop ozone, decreasing its negative effects. But when there is too much ozone, plants close all their stomata and in this case they suffer from shortage of carbon dioxide, a process that stops photosynthesis.
The research team experimented on plants the effects of human-induced rising ozone and carbon dioxide levels on plant photosynthesis. Indeed, higher carbon dioxide levels do increase plant productivity and carbon uptake, but higher ozone levels inhibit this process, so that the uptake won't be as high as researchers have believed.
The ozone itself is a greenhouse effect gas, boosting even by itself more global warming.
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