Climate change linked with rise of world's earliest civilisations

Past changes to the climate that generated increasingly arid conditions for ancient peoples helped to trigger the rise of the earliest civilisations on three continents, a study has found.

The ancient civilisations of Egypt, Mesopotamia, south Asia, China and northern South America all owe some of their initial success to significant changes in rainfall and temperature, a climatologist said yesterday.

The conventional view of how early civilisations developed is that they benefited from the steady conditions of a predictable period of climate constancy.

However, Nick Brooks, a researcher at the University of East Anglia in Norwich, believes there is mounting evidence to show that past civilisations grew in response to climate change rather than being the result of climate stability.

"The earliest civilisations developed as a by-product of adaptation to climate change, and crucially that they were the products not of a benign environment, but of a hostile one," Dr Brooks told the British Association.

A study of the early Garamantian civilisation that developed 3,000 years ago in what is now the Sahara showed that increasingly dry conditions had led to an acceleration in the technological innovation and monumental architecture that are the hallmarks of civilisation. The Sahara was undergoing a dramatic change from a fertile region to one where most of the water was being concentrated around a series of lakes.

The change in the climate was matched by a change in the way of life of the local inhabitants, who began to congregate in relatively large population centres around the lakes.

As the lakes dried out they developed new strategies for survival and this is the time when archaeologists find the first evidence of agriculture, permanent structures and hand-dug wells. The Garamantians were skilled charioteers and their civilisation became powerful enough to challenge the Romans for dominance of north Africa.

The drying out of the Sahara also led people to migrate to the Nile valley, which flooded regularly to produce fertile fields that became the economic basis for the ancient Egyptian civilisation, he said. "Given those conditions around the Nile, that's the place where most people were going to congregate when the rest of the environment deteriorates," Dr Brooks said.

There is further evidence to suggest that climate change and increasing aridity may have helped to trigger the earliest civilisations of ancient Mesopotamia, in what is now Iraq, the Harappan culture of south Asia, and the ancient cities of northern China.

Dr Brooks said that the Pacific Ocean's El Niño climate anomaly may have also played a role in generating the arid conditions that were part of the reason why ancient civilisations grew out of the Peruvian mountains.

"In all the 'cradles of civilisation' we find evidence of dramatic social change during a time of profound environmental change, in the form of increased regional aridity," he said.