Satellite observations made from 1982 to 2010 found that warm, arid regions are getting greener. 

Researchers have long argued that increasing atmospheric carbon dioxide will fertilize enhanced plant growth because carbon dioxide is a fuel source for plants' photosynthesis. In water-limited regions an increased atmospheric carbon dioxide concentration would allow plants to absorb the gas they need, while minimizing water loss.

However, attributing the observed greening to the carbon fertilization effect rather than changes in water or nutrient availability or other factors is difficult because in warm, dry regions, plant growth is often controlled by water availability. In these areas the effects of carbon fertilization on foliage cover are expected to be most pronounced, and it is changes in cover that can be detected from satellites.

By focusing on arid regions worldwide and controlling observations of plant foliage cover change for differences in precipitation rate, Donohue et al. find that carbon fertilization has caused an 11 percent increase in foliage cover from 1982 to 2010. This increased foliage cover in areas such as the U.S. Southwest and Mexico, the deserts of Argentina, the Middle East, central and western Australia, and the regions that ring the Sahara was driven by a 14 percent increase in the atmospheric carbon dioxide concentration over the same period. 

The carbon fertilization effect is already a prominent driver of land surface processes, at least in warm, arid environments. The authors note that though carbon fertilization may be occurring in some way in other ecosystems, the same strong relationship between increasing atmospheric carbon dioxide and foliage cover likely does not extend globally.

Source: Randall J. Donohue, Tim R. McVicar, Michael L. Roderick, Graham D. Farquhar, 'Impact of CO2 fertilization on maximum foliage cover across the globe's warm, arid environments', Geophysical Research Letters Volume 40, Issue 12, pages 3031–3035, 28 June 2013 DOI: 10.1002/grl.50563