How the Pacific Ocean changed history

Egypt 's Old Kingdom was the age of pyramids, the first flourishing of civilization along the River Nile lasting for approximately half a Millennium from 2700 to 2200 BC .

Scientists think that at least a major contributing factor to the downfall of the Old Kingdom and several other kingdoms at the same time, was a persistent change in the weather in the Nile .

There's a huge overturning circulation of air that reaches across the Pacific called the Walker Circulation .

This is driven by a difference in surface pressure between the east and west Pacific .

In El Nino conditions, the Walker circulation weakens or reverses, and so less water is transported across the ocean and less is drawn from the depths of the coast of South America , meaning the water there is warmer than normal.

In La Nina , the opposite is true. The Walker circulation is stronger than normal, which means more water and more water up wells.

Around 4200 years ago , several societies collapsed at about the same time, including the Old Kingdom in Egypt , the Acadian Empire in Mesopotamia , and the Indus Valley civilization in India .

This would point to a shift in regional climate distant with the impacts of a strong persistent El Nino phase of ENSO .

Not everyone agrees that these events were contemporaneous or connected.

But we have more concrete evidence that other societies were challenged and found wanting by changes in climate in South America .