During the last glaciation, for at least 50,000 years prior to 18,000 years ago, the temperature of Africa must have been lower than the present, probably by some 5° C at the glacial maxima. The corresponding reduction in evaporation would have increased the effectiveness of the rainfall.
Owing to the surface relief of the continent the reduction in temperature would have enormously extended the area of the montane biomes of tropical Africa at the expense of the lowland, except west of the Cameroons. Continuous communication for montane species, which are at present reduced to isolated and small areas, would have been open from the Cameroon highlands to Abyssinia and South Africa.
Changes of similar magnitude would be expected with each glaciation.
Apart from these general effects there is geological evidence for sub-regional fluctuations on a large scale; the dating and the relationship of some of them to the glacial variations remain to be established. The most important are the southward movement of Palaearctic communities at least 400 miles into the Sahara, the northward movements of the Sudanese climatic belts, bringing the Sahelian biome at least 300 miles north, on the last occasion around only 7,000 years ago, the extension of Lake Chad to about four times the size of Lake Victoria, which implies a northward movement of the equatorial rain-belt over the southern edge of its basin, the southward movement of the Sudanese climatic belts, with fragmentation of the Upper Guinea forests, the fragmentation of the main Congo (Lower Guinea) forest prior to about 60,000 years ago and the desiccation of an area covering eastern Angola, the middle Zambesi and probably the south of the Congo basin as recently as 12,000 years ago.
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