Natural Aridification or Man-Made Desertification? A Question for the Future

  • N. Petit-Maire
Part of the NATO ASI Series book series (ASIC, volume 325)


1) In the last 150 ka, the tropical arid belt in North Africa (Sahara) and its southern margins (Sahel) successively underwent major changes in their latitudinal range:
  • 130 ka: extensive lakes throughout present Sahara

  • 18 ka: Saharan environments down to 14°N

  • 8–7 ka: Sahelian environments up to 22–23°N.

These continental processes coincide with sea level transgressive and regressive phases and the Milankovitch forcing.

2) Since c 4.500 B.P., another expansion of the Sahara has taken place. The Sahel’s northern limit, now at 17° N is still regressing southwards. These data demonstrate a trend towards an arid scenario and match the insolation curve since 10 ka ago and the future cold trend calculated by A. Berger (1981).

The natural climatic forcing therefore runs counter to an eventual greenhouse effect, as it would be once again associated with temperature and sea-level drops.

The evidence for climatic changes in the north african arid belt thus confirms the predictive model of Kukla (1980) and does not imply any responsibility of man, although deforestation and erosion locally emphasize the trend.

Changes in rainfall, increase in deforestation and erosion recorded both in the tropical belts and in the Mediterranean borders, the possible rise of oceanic vapour and precipitation due to a CO2 greenhouse effect and the recent increase in strength and frequency of the dominant winds in the northern hemisphere are different factors which should be considered carefully and separately before one can imply any valuable theory on future global evolution. In the tropical arid belt enough field data are now available to allow a useful interpretation of environmental changes during the last global climate cycle and to define the part played by man in long trend variations and compare them with shorter term observations.

Successive extensions and shrinkings of the arid zone of North Africa (< 100–150 mm annual precipitation and 4–8 m evapotranspiration) are in evidence for the last 150 ka and are obviously related to marine isotopic trends (Hays and Imbrie, 1986) sea levels (Shackleton et al., 1981) and the astronomical Milankovitch insolation curve at 65°N (Berger, 1981, 1984).


Tropical Belt Short Term Observation Valuable Theory Regressive Phasis Oceanic Vapour 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Ballais, J.L. & Ben Ouezdou, H. (1987) “Formes et dépots du Quaternaire continental de la bordure présaharienne du Maghreb oriental. Essai de synthèse proviso ire”, Conference P.I.C.G. 210, pp. 18–19Google Scholar
  2. Berger, A. (1981) “The astronomical theory of palaeoclimates”, in A. Berger (ed.) Climatic variations and variability: facts and theories, Dordrecht, Reidel, pp. 501–525Google Scholar
  3. Berger, A. (1984) “Accuracy and stability of the Quaternary terrestrial insolation”, in Milankovitch and Climate, 1, pp. 83–111Google Scholar
  4. Callot, Y. (1985) “Dépôts lacustres et palustres quaternaires de la bordure nord du grand Erg Occidental (Algérie).”, Comptes-Rendus de l’Academie des Sciences, Paris (D), 299, pp. 1347–1350Google Scholar
  5. Fabre, J. (1983) “Esquisse sratigraphique préliminaire des dépôts lacustres quaternaires”, in N. Petit-Maire and J. Riser, (eds.) Sahara ou Sahel? Quaternaire récent du Bassin de Taoudenni, pp. 421–441Google Scholar
  6. Fabre, J. & Petit-Maire, N. (1988) “Holocene climatic evolution at 22°–23°N from two palaeolakes in the Taoudenni area (northern Mali)”, Paleaogeography, Paleaoclimatology, Palaeoecology, 65, pp. 133–148CrossRefGoogle Scholar
  7. Faure, H. (1969) “Lacs quaternaires du Sahara”, Mitt, intern. Verein. Limnol., 17, pp. 131–146Google Scholar
  8. Fontes, J.C., Gasse, F., Callot, Y., Plaziat, J.C., Carbonel, P., Dupeuble, P. & Kaczmarska, I. (1985) “Freshwater to marine-like environments from Holocene lakes”, in northern Sahara, Nature, 317, pp. 608–610CrossRefGoogle Scholar
  9. Gasse, F., Fontes, J.C., Plaziat, J.C., Carbonel, P., Kaczmarska, I., De Deckker, P., Soulie-Marsche, I., Callot, Y. & Dupeuble, P.A. (1987) “Biological remains, geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the Holocene lakes form North Sahara”, Palaeogeography, Palaeoclimatology, Palaeoecology, 60, pp. 1–46CrossRefGoogle Scholar
  10. Gaven, C., Hillaire-Marcel, C. & Petit-Maire, N. (1981) “A Pleistocene lacustrine episode in southeastern Libya”, Nature, 290, pp. 131–133CrossRefGoogle Scholar
  11. Hays, J.D., Imbrie, J. & Shackleton, N.J. (1976) “Variations in the Earth’s orbit: pacemaker of the Ice Ages”, Science, 194, pp. 1121–1132CrossRefGoogle Scholar
  12. Kröpelin, S. (1987) “Palaeoclimatic evidence from early to mid-Holocene playas in the Gilf Kebor (southwest Egypt)”, in Coetzee, J. A. (ed.) Palaeoecology of Africa, vol. 18, Balkema, Rotterdam, pp. 189–208Google Scholar
  13. Kukla, G. (1980) “End of the last Interglacial: a predictive model for the future?”, Palaeoecology of Africa, 12, pp. 395–408Google Scholar
  14. Leroux, M. (1987) “L’Anticyclone mobile polaire, relais des échanges méridiens: son importance climatique”, Géodynamique, vol. 2, ORSTOM, pp. 161–167Google Scholar
  15. Ousseini, I. & Morel, A. (1989) “Utilisation de formations alluviales azo ï ques pour l’etude des paléoenvironnemnets du Pléistocene supérieur et de l’Holocène au Sud du Sahara: l’exemple de la vallée du fieuve Niger dans le Liptako nigérien”, Bull. Soc. géol. France, 8, n° 1, pp. 85–90Google Scholar
  16. Pachur, H.J. & Kröpelin, S. (1987) “Wadi Howar: palaeoclimatic evidence from an extinct river system in the south eastern Sahara”, Science, 237, pp. 298–300CrossRefGoogle Scholar
  17. Petit-Maire, N. (ed.) (1982) Le Shati, lac pléistocène du Fezzan (Lybie), Paris/Marseille, CNRS, 118 p.Google Scholar
  18. Petit-Maire, N. (1986) “Palaeoclimates in the Sahara of Mali: a multidisciplinary study”, Episodes, 9 /1, pp. 7–16Google Scholar
  19. Petit-Maire, N., Casa, L., Delibrias, G. & Gaven, C. with an appendix by Testud, A.M. (1980a) “Preliminary data on quaternary palaeolacustrine deposits in the Wadi ash Shati, Libya”, in Salem, M.J., and Busrewil, M.T. (eds.) The geology of Libya, 3, London, Academic Press, pp. 797–807Google Scholar
  20. Petit-Maire, N., Fabre, J., Carbonel, P., Schulz, E. & Aucour, A.M. (1987) “La depression de Taoudenni (Sahara malien) à l’Holocène”, Géodynamique, 2 /2, pp. 61–67Google Scholar
  21. Petit-Maire, N. (1989) “Interglacial environments in presently hyperaid Sahara: Paleoclimatic implications”, in Proceedings, NATO Advanced Research Workshop on Plaeoclimatology and Paleometeorology, Kluwer Academic Publishers (in press)Google Scholar
  22. Petit-Maire, N., Delibrias, G. & Gaven, C. (1980) “Pleistocene lakes in the Shati area, Fezzan (27°3’N)”, Palaeoecology of Africa, 12, pp. 289–295Google Scholar
  23. Petit-Maire, N. & Riser, J. (1981) “Holocene lake deposits and palaeoenvironment in central Sahara, northeastern Mali”, Palaeogeography, Palaeoclimatology, Palaeoecology, 35, pp. 45–61CrossRefGoogle Scholar
  24. Petit-Maire, N. & Riser, J. (ed.) (1983) Sahara ou Sahel? Quaternaire récent du basin de Taoudenni (Mali), Marseille, 473 p.Google Scholar
  25. Shackleton, N.J. et al. (1982) “The Deep-Sea Sediment Record of Climate Variability”, Prog. Oceanogr., 11, pp. 199–218CrossRefGoogle Scholar
  26. Szabo, B.J., McHugh, W.P., Sċhaber, G.G., Haynes Jr, C.V. & Breed, C.S. (1989) “Uranium-Series Dated Authigenic Carbonates and Acheulian Sites in Southern Egypt”, Science, 243, pp. 1053–1056CrossRefGoogle Scholar
  27. Talbot, M. (1984) “Late pleistocene rainfall and dune building in the Sahel”, in Coetzee, J. A., and Van Zinderen Bakker, A.M. (eds.) Palaeoecology of Africa, 16, Balkema, Rotterdam, pp. 203–214Google Scholar

Copyright information

© Kluwer Academic Publishers 1990

Authors and Affiliations

  • N. Petit-Maire
    • 1
  1. 1.Laboratoire de Geologie du QuaternaireCNRSMarseille CedexFrance

Personalised recommendations