Th e evidence paints an overall picture of increased
warming and wetness across Africa over time, but the picture
is fragmented both spatially and geographically. Climate-
change data are not available for all locations or for each year.
Furthermore, there is variability in the climatic conditions
of particular regions during the general period of increased
humidity. For example, there is no evidence that the desert
areas of present-day Libya and western Egypt (northern Af-
rica) also experienced a much more vegetated state. South
Africa provides data that indicate a general warming trend
with increasing moisture in some areas, but data from south-
ern Africa’s Kalahari and Namib deserts indicate more severe
dryness. Evidence from Lake Tanganyika, an extremely deep
lake in the Rift Valley, shows a reduction in forest cover in the
surrounding area around the same time.
Some parts of Africa experienced a more minor dry peri-
od (compared with the last major ice age) again around 7,500
to 8,000 years ago. Ice cores from glaciers on Mount Kiliman-
jaro that also have been used to reconstruct the details of past
climatic conditions show a brief but intense drying period
some 8,300 years ago. In many areas of Africa there was an-
other period of increased moisture until about 4,000 to 5,000
years ago. Th is humid period was apparently much shorter
in the area north of the Algerian Sahara than in the central
mountains. During this last humid period, areas south of
the Sahara were oft en fl ooded, and the waters of Lake Chad,
the Niger River, and the Senegal rivers were at record-high
levels. Ice cores from Mount Kilimanjaro date this period of
increased moisture to 5,200 years ago and associate it with
cooler temperatures (rather than warm temperatures, which
oft en seem to be associated with increased moisture in Afri-
can climate history).
END OF THE HUMID PERIOD
About 4,000 to 5,000 years ago the temperatures started to
drop again, and conditions became much drier. Vegetation
began to change as forests shrank and sand dunes formed in
the Sahara. Th e glaciers on Mount Kilimanjaro retreated. An-
imals and people migrated out of the inner Sahara to escape
the increasingly dry hostile conditions. Data recovered from
caves and cliff s in eastern Libya that show a gap in evidence of
human occupation some 5,000 years ago have been compared
with other climate data and have indicated increased dryness
there. It is thought that humans migrated out of the area at
the onset of drought conditions.
Cave paintings and human settlement remains from
Mauritania (in northern Africa) suggest that humans mi-
grated from farther north to this area around 4,000 years
ago in an attempt to escape the onset of drier conditions.
Th ere is also evidence of the dispersal of cattle from the dri-
er areas of western and northwestern Africa around 3,700
years ago and from the Sudan and Niger 4,000 to 4,500 years
ago. Water levels lowered in the areas of present-day Ghana,
Sudan, Ethiopia, and Uganda. Th is period, referred to as the
First Dark Age, includes a severe 300-year drought in tropi-
cal Africa that began about 4,000 years ago. Starting some
5,000 years ago, many of the lakes in southern Africa also
began gradually drying out, and about 2,000 years ago the
forests of present-day Senegal and those surrounding Lake
Chad had been depleted, causing a change in the composi-
tion of species inhabiting the area. Evidence of the start of
this cooler drying period is also present in data from other
tropical areas around the world, suggesting a global change
in climate.
As the Sahara dried out, the Nile River valley, along with
the area encompassed by the Tigris and Euphrates rivers, be-
came a center for human civilizations. Th e Nile, at 4,146 miles
long (8,671 kilometers), is the longest river in the world. It
also has experienced predictable fl ooding through centuries,
which has provided relief during dry periods for humans and
animals living in the surrounding area. Annual fl oods contin-
ually renew the soils with a deposit of fertile silt on a continent
characterized by ver y old soi ls t hat have over time lost ma ny of
the nutrients that support productive agriculture.
Humans have migrated to the Nile Valley many times
throughout history during periods of harsh climatic condi-
tions. Many scientists have found data, for example, that
point to bursts in population and social development in
this region during periods of drought in the Sahara. Fossil
records of fl ora and fauna provide information on the pres-
ence and migration patterns of humans, domestic animals,
and wild animals as well as data on vegetative cover. Th ese
data have been used to date major migrations into and out
of today’s Sahara that coincide with evidence of extreme
conditions in the Sahara. Migrations out of the Sahara, as-
sociated with the environmental pressure of drought, may
have contributed to increased confl ict over hospitable land,
such as the wars between the Egypt and Libya in about
1200 b.c.e.
Traditionally, migration has been a survival strategy
commonly used by social groups in Africa to deal success-
fully with climate changes. For those peoples that did not
migrate during periods of increased dryness in Africa,
adapting livelihood strategies was essential. As a result of
drought conditions around 4,000 years ago, livelihood ac-
tivities such as pastoralism in East Africa and agriculture
in West Africa, including the use of specifi c techniques
such as terracing and dams, expanded as people adapted to
the diff erent environmental conditions. Other data refl ect
that during drought conditions in Africa from 1200 to 2100
b.c.e. some Saharan communities developed and extended
mining activities in order to trade for food with communi-
ties to the south.
Africa’s unique geography and global climatic context
jointly have aff ected specifi c regions of the continent diff er-
ently during ancient times. Resulting changes in ecosystems
led to variations in human settlement and activity patterns
during this time period. Th ese shift ing patterns did not occur
in a vacuum but were part of a larger-scale system of global
variation in geography and climate.238 climate and geography: Africa