"Considerable controversy exists over the proper definition of the term "desertification" for which Helmut Geist (2005) has identified more than 100 formal definitions.The most widely accepted[2] of these is that of the Princeton University Dictionary which defines it as "the process of fertile land transforming into desert typically as a result of deforestation, drought or improper/inappropriate agriculture"[4]"

source: http://en.wikipedia.org/wiki/Desertification


The inability to get figures on desertification means a significant indicator of the system awaits us all...

The above highlights why the figures are difficult to come by: lack of definition!!

==> It's always a measurement problem in science: firstly, what do you measure?... secondly, how??

With figures you can graph them with respect to time and find slopes of change, and slopes of the slopes of change...  8-)