There are examples of long term progressive dessication, but overall, it has NOT been the main cause of desertification. The process of desertification is advancing world wide with a rapidity that threatens the agricultural productivity of not only the Third World nations, in particular, the African nations such as Ethiopia, Chad, Senegal and Niger, but also countries such as Mexico along with extensive areas of the First World countries such as the United States of America and Australia. Figure 1 shows the world wide distribution of desertified areas. That area is equivalent to the whole of North America and South America combined. Expressed another way, desertification already affects one third of the ice-free land areas of our planet.
Desertification affects all types of agricultural lands.
The Canterbury Plains, New Zealand. Figure 3 Extreme desertification in the in late summer South African veldt Each year 6 million hectares of productive agricultural land is lost through desertification and another 21 million hectares are so impoverished that the land is barely useable. Projecting this trend to the year 2000 gives the frightening statistic that the livelihood of 1.2 billion people world wide will be affected, or about one-sixth of the world population. To feed this number will demand even greater intensification on the remaining agriculturally productive areas, it will demand greater movement of food from areas of surplus to areas of deficit, it will need greater political co-operation between governments of the world with mechanisms in place where by the poorest food deficient countries can pay for their food imports not in cash but in some other way. Traditionally, the northern industrialised countries have been prepared to take natural resources in place of hard currency payments, notably oil, or tropical timber, cane sugar.