The Sahara turned from grassland to desert 4,000 years ago, triggering a mega-drought in Southeast Asia

A mega-drought that raped Southeast Asia 1000 years ago was triggered by the Sahara that went from lush grassland to a barren desert 4000 years ago, a study found.

The end of the ‘Green Sahara’ – also known as the ‘African humid period’ – was caused by changing world water patterns draining the region.

The rise of the desert to which we are accustomed today has long been studied by archaeologists for its influence on human civilizations of the time.

For example, it led to the end of the Akkadian Empire of Mesopotamia, the de-urbanization of the Indus Civilization and the emergence of pastoralism by the Nile.

However, experts from the US found evidence in caves in Laos that it was also behind the ‘missing millennia’ in the archaeological record of Southeast Asia.

The mega-drought that it caused would have led to mass population movements and the adoption of new, more skilled subsistence strategies.

It may even have led to the beginning of the Neolithic on mainland Southeast Asia, the researchers concluded.

“We provide the first evidence of a strong link between the end of the Green Sahara and Southeast Asian monsoon falls in the mid to late Holozene period,” said Earth scientist Kathleen Johnson of the University of California, Irvine.

‘Our high resolution and well-dated record suggests a strong connection between North Africa and mainland Southeast Asia at this time.’

In their study, Professor Johnson and colleagues reconstructed the climate of the past by analyzing samples of stalagmites taken from caves in Northern Laos for diagnostic oxygen and carbon isotope levels and trace metals.

They combined these data with climate simulations enabling them to investigate the impact on the long-term dryness of Africa – including on atmosphere – ocean feedback – based on varying levels of Sahara vegetation and dust concentrations.

The researchers found that the decline in vegetation in the Sahara region 4000 years ago led to an increase in dust in the air.

This cools the Indian Ocean, shifting eastward the so-called Walker circulation pattern that crosses the equatorial Pacific Ocean today – causing it to behave in a manner similar to current El Niño events.

This shift led to a large reduction in monsoon-related moisture in Southeast Asia that lasted at least 1,000 years, Professor Johnson said.

‘Archaeologists and anthropologists have been studying this event for decades, in terms of social adaptations and circumstances,’ said paper author and environmental scientist Michael Griffiths of William Paterson University, NJ.

However, he added, ‘the exact cause has distracted the scientific community.’

‘Results of this work provide a new and convincing explanation for the origins of the mega-drought of Southeast Asia and could help us better understand […] the observed social shifts across many parts of the tropics and extra-tropics. ‘

“This is excellent evidence of the type of climate change that must have affected society, what plants were available, what animals were available,” said paper author and anthropologist Joyce White of the University of Pennsylvania.

‘All life had to adapt to this very different climate. From an archaeological point of view, this is really a game changer in how we try to understand or reconstruct the Middle Holozene period. ‘

The full findings of the study were published in the journal Nature Communications.