October 23, 2013

CO2 Fertilization and Climate Change

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Australian researchers have found that increased levels of carbon dioxide contribute to making the world’s driest regions greener. The study, conducted by the Commonwealth Scientific and Industrial Research Organisation of Australia and Australian National University, identified an 11 percent increase in foliage in arid regions between 1982 and 2010 that strongly correlated with increasing levels of CO2.

In what is called the fertilization effect, plants take up increasing levels of CO2 and photosynthesize more rapidly, thus decreasing atmospheric CO2 levels. According to CSIRO, the researchers predicted that foliage in dry areas would grow more, because at higher levels of CO2, arid plants use water more efficiently. The researchers then observed satellite data of arid regions in the world.

“Drylands would be expected to be most responsive to the carbon dioxide fertilization effect. One intriguing implication is that the observed invasion of woody plants into dry grasslands may be caused in part by this effect,” Prof. Timothy Fahey, Department of Natural Resources, said.

According to Dr. Randall Donohue, CSIRO, these results should not be interpreted as support for climate skeptics and do not mean that climate change is good. Rather, the study forays into a particular area of climate research that has long been difficult to observe.

“CO2 fertilization has been shown in greenhouse and field experiments, but this enhancement has been hard to detect in the natural environment,  as reported here,” Prof. Christine Goodale, Department of Ecology and Evolutionary Biology, said. However, “the growth enhancement offsets only a tiny fraction of the CO2 emissions released to the atmosphere from fossil fuel combustion.”

According to Goodale, some plants are more sensitive to rises in CO2 than others, which could have an effect on interpreting foliage growth.

“Most global climate models use basic physiological relationships among CO2, photosynthesis and water use to project rather optimistic CO2 fertilization responses over the coming centuries,” Goodale said.