There has been an increase in vegetation in the arid regions of the world since the 1980s, mostly due to an increase in the levels of carbon dioxide, a new study has reported.

Researchers from Commonwealth Scientific and Industrial Research Organization studied the carbon dioxide "fertilization effect" on many regions, including southwestern corner of North America, Australia's outback, the Middle East, and parts of Africa. The study team used mathematical models to predict the extent of the fertilization effects. Satellite images of the region were also used to account for other factors that may have impacted the "greening of arid regions", such as amount of light, temperature, rainfall and land-use changes.

The study is published in the journal Geophysical Research Letters.       

The mathematical model predicted that during the study period, the amount of greenery in these regions would increase by 5 to 10 percent, given that the carbon dioxide would increase by 11 percent.

The satellite images supported this prediction by showing that there was an 11 percent increase in foliage, even after adjusting for other factors.

"Lots of papers have shown an average increase in vegetation across the globe, and there is a lot of speculation about what's causing that. Up until this point, they've linked the greening to fairly obvious climatic variables, such as a rise in temperature where it is normally cold or a rise in rainfall where it is normally dry. Lots of those papers speculated about the CO2 effect, but it has been very difficult to prove," said Randall Donohue of CSIRO's Land and Water research division, lead author of the study.

Donohue explained that the satellite images showed the extent of leaf cover in arid regions. Plants tend to produce more leaves if there is an increase in carbon dioxide levels and less water to use.

Also, the study found that change in the carbon dioxide levels is changing the vegetation type. For example, trees are re-invading grasslands. Donohue said that long-lived woody trees are more likely to benefit from a change in the carbon dioxide levels than grasses.

"The effect of higher carbon dioxide levels on plant function is an important process that needs greater consideration," said Donohue in a news release. "Even if nothing else in the climate changes as global CO2 levels rise, we will still see significant environmental changes because of the CO2 fertilization effect."