Increased Carbon Dioxide Turns Arid Regions Green: Fertilizing the Desert

Since the 1980s, scientists have noticed green foliage flourishing across the globe in satellite images. Now, new research reveals that foliage in arid regions is springing to life partly due to an increase in carbon dioxide.

In order to study this greening effect, researchers focused on specific arid regions. They looked at the southwestern corner of North America, Australia's outback and some parts of Africa. The researchers then developed and applied a mathematical model to predict the extent of the carbon dioxide fertilization effect. They then tested this prediction by studying satellite imagery and teasing out the influence of carbon dioxide on greening from other factors such as precipitation, air temperature, the amount of light and land-use changes.

"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," said Randall Donohue of the Commonwealth Scientific and Industrial Research Organization, in a news release. "Up until this point, they've linked the greening to fairly obvious climactic 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."

The researchers' models did indeed prove that carbon dioxide was influencing the foliage across the Earth. In fact, they actually predicted that foliage would increase by five to ten percent given the 14 percent increase in CO2 during the study period. The satellite data agreed; it showed an 11 percent increase in foliage after adjusting the data for precipitation.

While some areas may experience an increase in foliage with increased carbon dioxide, though, other places will not. For example, tropical rainforests already have extensive foliage cover. Therefore, it's unlikely that cover will increase with higher CO2 concentrations. Yet this greening effect won't only cause foliage to increase. It may also change the composition of plants in an area.

"Trees are re-invading grass lands, and this could quite possibly be related to the CO2 effect," said Donohue in a news release. "Long lived woody plants are deep rooted and are likely to benefit more than grasses from an increase in CO2."

The findings have enormous implications for how our Earth is changing due to a subsequent change in CO2 levels and climate. In a few years, we could see some significant changes due to this CO2 fertilization effect.

The findings are published in the journal Geophysical Research Letters.