Herrmann, S.M., Anyamba, A. and Tucker, C.J. 2005. Recent trends in vegetation dynamics in the African Sahel and their relationship to climate. Global Environmental Change 15: 394-404.
There has been a long history of assertions of widespread and irreversible desertification occurring in the Sahel of Africa (Dregne, 1983; Lamprey, 1988; Middleton et al., 1997). During the 1970s, in particular - when Lamprey's report was originally written - the United Nations spearheaded a massive media campaign to warn the world about the phenomenon; and as recently as August 2002, leaders of the UN Environment Program told the World Summit on Sustainable Development held in Johannesburg that over 45% of the continent was at that time experiencing severe desertification. Several years earlier, however, scientists had already begun to realize that these assertions were no longer true, as demonstrated by the work of Nicholson et al. (1998) and Prince et al. (1998) , which fact has been confirmed by the more recent studies of Eklundh and Olsson (2003), Anyamba and Tucker (2005) and Olsson et al. (2005), as reported in our Editorial of 11 Jan 2006.
What was done
Herrmann et al. provide addition support for the newer findings as a result of their investigation of "temporal and spatial patterns of vegetation greenness and rainfall variability in the African Sahel and their interrelationships based on analyses of Normalized Difference Vegetation Index (NDVI) time series for the period 1982-2003 and gridded satellite rainfall estimates."
What was learned
For the period 1982-2003, the three researchers determined that "the overall trend in monthly maximum NDVI [was] positive over a large portion of the Sahel region, reaching up to 50% increase in the average NDVI in parts of Mali, Mauritania and Chad." In addition, they found that "rainfall emerges as the dominant causative factor in the dynamics of vegetation greenness in the Sahel at an 8 km spatial resolution," but that "the presence of spatially coherent and significant long-term trends in the residuals suggests that there might be another, weaker, causative factor," which is also suggested by the fact that the "recovery of vegetation greenness [was] beyond what would be expected from the recovery of rainfall conditions alone."
What it means
Herrmann et al. state that their study "confirms previous regional-scale findings for the period 1982-1999 by Eklundh and Olsson (2003) and Olsson et al. (2005), who observed widespread positive trends of both time-integrated NDVI and NDVI amplitudes, and Anyamba and Tucker (2005), who [observed] increases in growing season NDVI across most parts of the region." In concluding, they thus say that "a greening of the Sahel expressed in positive trends in NDVI indicates a net increase in biomass production during the period 1982-2003, which challenges the notion of irreversible desertification in the Sahel."
We would only add that this positive development has occurred in the face of the concurrent expression of the twin evils of the radical environmentalist movement, i.e., increases in atmospheric CO2 concentration and air temperature that are claimed to be unprecedented over the past two millennia or more, which should lead one to wonder: are these phenomena really the greatest threat facing the planet today, as members of this movement claim? Maybe more CO2 and warmth are not so bad after all. Indeed, maybe they're not bad at all. In fact, maybe they're actually good.
Anyamba, A. and Tucker, C.J. 2005. Analysis of Sahelian vegetation dynamics using NOAA-AVHRR NDVI data from 1981-2003. Journal of Arid Environments 63: 596-614.
Dregne, H.E. 1983. Desertification of Arid Lands. Harwood Academic Publishers, New York, NY, USA.
Eklundh, L. and Olsson, L. 2003. Vegetation index trends for the African Sahel 1982-1999. Geophysical Research Letters 30: 10.1029/2002GL016772.
Lamprey, H.F. 1988. Report on desert encroachment reconnaissance in Northern Sudan: 21 October to 10 November 1975. Desertification Control Bulletin 17: 1-7.
Middleton, N., Thomas, D. and United Nations Environment Programme. 1997. World Atlas of Desertification. Arnold, London, UK.
Nicholson, S.E., Tucker, C.J. and Ba, M.B. 1998. Desertification, drought, and surface vegetation: An example from the West African Sahel. Bulletin of the American Meteorological Society 79: 815-829.
Olsson, L., Eklundh, L. and Ardo, J. 2005. A recent greening of the Sahel - trends, patterns and potential causes. Journal of Arid Environments 63: 556-566.
Prince, S.D., Brown De Colstoun, E. and Kravitz, L.L. 1998. Evidence from rain-use efficiencies does not indicate extensive Sahelian desertification. Global Change Biology 4: 359-374.Reviewed 7 June 2006