"More recently, Zhou et al. (2001) used satellite measurements to demonstrate
how vegetative activity increased by slightly over 8% and 12% between 1981
and 1999 in North America and Eurasia, respectively; while Ahlbeck (2002)
employed statistical procedures to demonstrate that the primary driver of
this phenomenon was the concurrent rise in the air's CO2 content, with
regional warming playing a secondary role. When some controversy arose over
this conclusion (Kaufmann et al., 2002), we confirmed Ahlbeck's assessment
of the situation by means of a quantitative comparison of what was observed via satellite and what would have been expected on the basis of the known strength of the aerial fertilization effect of the increase in atmospheric CO2 concentration that occurred over the period in question (see our
Editorial of 18 September 2002)."
http://abob.libs.uga.edu/bobk/ccc/cc111202.html

The extreme enviromentists see to think global CO2 levels will continue to rise, if this is true that perhaps the Sahara desert will "naturally" become more greener. Or perhaps plans could include inceasing CO level in locally.