Deserts of the World - Design with the Desert: Conservation and Sustainable Development - page 27

climatic belts. Second, because of the rise of the great Cenozoic mountain systems caused
by plate collision, rainshadow deserts were created on the continents, especially in Asia,
northern Argentina, the southwestern United States, and the Atlas. Third, changes in the
configurations of the oceans and continents caused a general world cooling: the so-called
Cenozoic climatic decline. Such cooling would have affected the nature and intensity of the
general atmospheric circulation and of ocean currents. The significance of this last point
is that in the Southern Hemisphere, the continents all have dry zones along their western
margins. Each of these deserts is to a large degree caused by an upwelling of cold water
off the coast, and such cold water is mostly of Antarctic origin. Such cold currents would,
therefore, not exist until Antarctica was producing large quantities of cold meltwater and
sea ice. For this to happen, Antarctica had to have moved to a suitable latitudinal position
following its separation from Australia. 126 These sorts of influences are seen in the history
of the Atacama Desert, an area which has been arid since at least the late Eocene. The uplift
of the Central Andes cordillera during the Oligocene and early Miocene was one critical
palaeoclimatic factor, providing a rain shadow for precipitation from the Amazon basin,
and stabilizing the southeastern Pacific anticyclone. However, it was the dramatic cooling
of Antarctic bottom waters and of the Humboldt Current around 13-15 million year BP,
associated with the formation of the Antarctic ice sheet, that enabled hyperaridity to be
established for the first time in the area. 110
1.11 Postscript
Since the writing of this chapter was completed in 1992, there have been some major
changes in our knowledge of the nature and history of the world's main deserts. 127 These
have been brought about by such factors as new dating techniques (e.g., optical dating)
and the development of methods for high-resolution environmental reconstruction. In
addition, our knowledge has been greatly expanded as a result of the availability of free
remote sensing imagery of increasingly high resolution and also the growth of indigenous
studies of deserts, most notably in China. We now have a clearer idea of the antiquity of
deserts of the climate changes that have taken place in the Quaternary and the distribution
and characteristics of such features as sand sea, pans, and yardangs. The burgeoning
of quaternary sciences has indicated the degree, frequency, and abruptness of climatic
changes in the world in general and in deserts in particular. We now have a far better
appreciation of changes at millennial, century, and decadal time scales.
References
1. A. Mangin, The Desert World (London, U.K.: Nelson, 1869).
2. P. Meigs, The world distribution of arid and semiarid homoclimates, in Reviews of Research on Arid
Zone Hydrology , pp. 203-209 (Paris, France: UNESCO, 1953); C. C. Wallen. Aridity definitions
and their applicability. Geografiska Annaler 49 (1967): 367-384; G. M. Howe et al., Classification
of world desert areas (U.S. Army National Laboratories Technical Report 69-38-ES, 1968); M. I.
Budyko, Izmeniya Klimata . Gidrometeoizdat, also published as: M. I. Budyko, Climatic changes