Background
A number of papers over the past few years have indicated that the African Sahel has been "greening up," as described in our Summary of the subject, which finding, in the words of Seaquist et al., "challenges the entrenched, popular notion of widespread land degradation (e.g. UNEP, 1992)." In the current study, therefore, they provide important new details about this largely unacknowledged phenomenon in terms of both its spatial and temporal variability.

What was done
The authors used a satellite data-driven light-use efficiency model to assess changes in absolute amounts of net primary production (NPP), expressed as carbon content, and its inter-annual variability in the African Sahel for the period 1982-1999.

What was learned
Seaquist et al. report that an extensive, albeit discontinuous, east-west band of NPP increase (>10 g C m^-2 year^-1) was identified, extending up to about 17°N, including several hotspots (>20 g C m^-2 year^-1) in central Senegal, south-western Mali, southern Chad, southern Sudan, as well as the Ivory Coast and southern Benin. For the Sahel in its entirety, they determined that the mean rate of change per pixel was 8.4 g C m^-2 year^-1, which yields a total mean rate of change of 51.0 Mt C year^-1 and an absolute net gain in NPP over the entire 18-year period of 918.0 Mt C. In addition, they report that "this increase is associated with a decrease in the inter-annual variability of NPP for the 1990s compared to the 1980s," such that "overall, the increase in NPP through time appears to be associated with an increase in the stability of this ecosystem," with the changes in carbon capture and increase in stability being driven primarily by rainfall "followed by atmospheric CO2."

What it means
As the globe has experienced what climate alarmists decry as unprecedented increases in both air temperature and atmospheric CO2 concentration - the "twin evils" of the radical environmentalist movement - one of the more inhospitable stretches of land on earth, i.e., the Sahel, has experienced striking increases in vegetative productivity, suggesting that those twin evils may not be so evil after all!

Reference
United Nations Environment Program. 1992. World Atlas of Desertification. Edward Arnold, London, UK.