CO2 making the deserts bloom
One hypothesis about the effect of increasing carbon dioxide in our atmosphere now has significant supporting scientific evidence.
Scientists speculated that a "CO2 fertilization effect" would occur as CO2 levels rose. The fertilization effect proposes that additional CO2 in the air allows leaves to extract more carbon during photosynthesis at less water cost to the plant.
Plant cells are mostly water. Although a little water is used in the photosynthesis reaction, 98% of the water use related to photosynthesis occurs due to transpiration: when a plant leaf opens its stomata to take in carbon dioxide for photosynthesis, water evaporates out of the leaf. The dry air makes this effect even more pronounced in desert plants.
The net result of the CO2 fertilization effect should be more leaves, or larger leaves, as the plant builds more foliage with the resources available to it. But proving the CO2 fertilization effect requires eliminating other possible explanations for greener deserts -- including variation in precipitation, air temperatures, changes in light received, and land-use effects.
Scientists from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) in collaboration with the Australian National University (ANU) have untangled these confounding influences with the help of mathematical models and satellite imagery of the earth's arid regions. They found that an 11 percent average increase in foliage between 1982 and 2010 can be attributed to a CO2 fertilization effect.
On the face of it, elevated CO2 boosting the foliage in dry country is good news and could assist forestry and agriculture in such areas; however there will be secondary effects that are likely to influence water availability, the carbon cycle, fire regimes and biodiversity, for example.
Of course, the CO2 fertilization effect also implies more CO2 tied up in plant foliage, a potential "remediation" of higher CO2 levels: could this reverse the greenhouse effect? Don't get your hopes up; while this is one more amongst many feedback mechanisms that complicate predicting the outcomes of a warmer planet blanketed in CO2, it is not an answer. The increased foliage can provide only a small dent into CO2 levels overall, and this adjustment will fall in sync with falling CO2, thereby reducing the power of a CO2 fertilization effect to reverse global climate change.