Present climate and biological change - Climate Change: Biological and Human Aspects - page 208

of humid conditions 7550-6750 years ago and the start of a lengthy period of human
habitation to 4780 years ago: human settlement ended sometime around 4910-4760
years ago. Interestingly, the human remains found show a morphological, presumably
evolutionary, change across the periods of habitation (Sereno et al., 2008).
The disruption by Lakes Agassiz and Ojibway of the Broecker thermohaline cir-
culation 8200 years ago, which significantly cooled the northern hemisphere for
around a century (and less so for around three centuries), is also thought to have
affected Neolithic people in Europe and around the Mediterranean. In 2006 Bernhard
Weninger, Eva Alram-Stern, Eva Bauer and colleagues compared the climate record
with archaeological sites before and after this event using radiocarbon dating. They
found that there were major disruptions of Neolithic cultures in the Levant, north-
ern Syria, south-east Anatolia, Central Anatolia and Cyprus, all at the same time.
The influence of the event 8200 calibrated-years ago is best recognised in Central
Anatolia. There, the large and long-flourishing settlement at Catalh oyuk-East, which
had been inhabited for around a thousand years, was deserted quite abruptly. Of
course, as rainfall and climate belts shift there were winners as well as losers, and
many other major archaeological sites in the Eastern Mediterranean were first occu-
pied around 8200 years ago. For example, in north-west Anatolia there was Hoca
¸e¸me; in Greece there was Nea Nikomedeia, Achilleion and Sesklo; and in Bul-
garia there was Ovcarovo-Platoto. Others became deserted around this time, such as
in Cyprus: Khirokitia and possibly Kalavassos-Tenta. Interestingly, the researchers
found no site where there was continuous settlement across (before and after) the
event 8200 years ago. The researchers propose that the event triggered the spread of
Neolithic farmers out of Anatolia, into Greek Macedonia as well as into the fertile
floodplains of Thessaly, and simultaneously into Bulgaria and probably other regions
as well (but these were not yet researched at the time of Bernhard Weninger and
colleagues' work). Their results explain the transition from what archaeologists and
prehistorians call the Late Neolithic to the Early Chalcolithic and so the event could
have caused some very significant, irreversible and unexpectedly rapid changes to the
contemporary social, economic and religious lifestyle in large parts of western Asia
and south-east Europe. Yet small settlements (be they many, spread over a wide area)
are one thing, what of larger, more complex societies with some coordinating urban
habitation?
Early civilisations (with cities as opposed to small settlements) were also vulnerable
to climate change. For example, it is likely that the demise of the Akkadian empire
in Mesopotamia was climate-induced. This civilisation was arguably the Earth's first
empire. It was established sometime in the century beginning 4300 years ago by
Sargon of Akkad and ultimately covered Mesopotamia from the headwaters of the
Tigris and Euphrates Rivers to the Persian Gulf during the late third millennium .

Archaeological evidence has shown that this highly developed civilisation collapsed
abruptly 4170

bc

150 years ago, and quite probably this was related to a shift to
more arid conditions as part of what is sometimes called the 4.2 kiloyear event. At
the time there were widespread abandonments of the agricultural plains of northern
Mesopotamia and dramatic influxes of refugees into southern Mesopotamia. There
populations grew so much that a 180 km-long wall, the 'Repeller of the Amorites',
was built across central Mesopotamia to stem nomadic incursions to the south (Weiss,

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