Although scientists expected the global warming to spur plant growth, it appears that tropospheric ozone is actually reducing that growth by a considerable amount, leaving researchers with no alternative but to revise their predictions.

According to a study published in the latest issue of Nature magazine, tropospheric ozone- also known by its chemical formula O3 and different from stratospheric ozone, which protects Earth from the Sun’s noxious UV rays- is damaging plants, reducing their capacity to absorb greenhouse gases like CO2.

The chain reaction means that plants cannot incorporate further amounts of CO2, therefore global warming accelerates and scientists need to revise their theoretical models concerning climate change.

"Ozone could be twice as important as we previously thought as a driver of climate change," co-author Peter Cox, from the University of Exeter, UK, told the BBC News website.

Tropospheric ozone is also considered to be a greenhouse gas and its presence in the atmosphere has steadily grown since the 1850. Ozone closer to the ground is formed in a reaction between sunlight and other greenhouse gases such as nitrogen oxides, methane and carbon monoxide.

"As CO2 (carbon dioxide) increases in the atmosphere, that stimulates plant growth," Sitch said by telephone. He noted that many scientific simulations that predict the impact of global warming have included this effect but "they haven't included the other effect, the negative effect of ozone damaging productivity," said Stephen Sitch, a climate researcher at Britain's Met Office, which deals with meteorology.

Ozone enters plants through pores, called stomata, in the leaves. It then produces by-products that reduce the efficiency of photosynthesis, leaving the plants weakened and undersized.

Projections of this rise in ozone "could lead to significant reductions in regional plant production and crop yields," the researchers said in a statement.

"Carbon dioxide is the largest greenhouse warming gas but ... (ozone) is reducing plant productivity by an appreciable amount," Sitch said.