Sahara turned from lush green grassland to a barren wasteland just 4,000 years ago and triggered a megadrought that crippled Southeast Asia for 1,000 years
- Researchers reconstructed the past climate using evidence from caves in Laos
- They combined this with models to simulate the effects of the Sahara drying up
- The rise in airborne dust cooled the Indian Ocean, changing circulation patterns
- This greatly reduced monsoon-related moisture in parts of Asia for centuries
A megadrought that crippled Southeast Asia for 1,000 years was triggered by the Sahara going from lush grassland to a barren desert 4,000 years ago, a study found.
The end of the ‘Green Sahara’ — also known as the ‘African humid period’ — was brought about as changing world weather patterns caused the region to dry up.
The emergence of the desert we are familiar with today has long been studied by archaeologists for its impact on human civilisations of the time.
For example, it led to the end of Mesopotamia’s Akkadian Empire, the de-urbanisation of the Indus Civilisation 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 inner Southeast Asia’s archaeological record.
The megadrought it caused would have led to mass population movements and the adoption of new, more resilient subsistence strategies.
It may even have led to the inception of Neolithic farming in mainland Southeast Asia, the researchers have concluded.
A megadrought that crippled Southeast Asia for 1,000 years was triggered by the of Sahara going from lush grassland to a barren desert 4,000 years ago, a study found. Pictured, the Sahara desert today, with sand dunes seen in the background
‘We provide the first proof for a strong link between the end of the Green Sahara and Southeast Asian monsoon failure during the mid- to late Holocene period,’ said earth scientist Kathleen Johnson of the University of California, Irvine.
‘Our high-resolution and well-dated record suggests a strong connection between Northern Africa and mainland Southeast Asia during this time.’
In their study, Professor Johnson and colleagues reconstructed the climate of the past by analysing samples of stalagmites taken from caves in Northern Laos for the diagnostic oxygen and carbon isotope levels and trace metals.
They combined this data with climate simulations which allowed them to explore the long-range impact of the drying in Africa — including on atmosphere–ocean feedbacks — based on varying levels of Saharan vegetation and dust concentrations.
The researchers found that the reduction in plant growth in the Sahara region 4,000 years ago led to an increase in airborne dust.
This cooled the Indian Ocean, shifting eastward the so-called Walker circulation pattern which today crosses the equatorial Pacific— causing it to behave in a manner similar to modern-day El Niño events.
This shift led to a sizeable reduction in monsoon-related moisture across Southeast Asia that lasted for at least 1,000 years, Professor Johnson said.
‘Archaeologists and anthropologists have been studying this event for decades now, in terms of societal adaptations and upheavals,’ said paper author and environmental scientist Michael Griffiths of the William Paterson University, NJ.
However, he added, ‘its exact cause has eluded the scientific community.’
‘Results from this work provide a novel and convincing explanation for the origin of the Southeast Asia megadrought and could help us better understand […] the observed societal shifts across many parts of the tropics and extra-tropics.’
The end of the ‘Green Sahara’ — also known as the ‘African humid period’, which would have resembled the savannah of today’s Tanzania, pictured — was brought about as changing world weather patterns caused the region to dry up
‘This is outstanding evidence for 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 of life had to adjust to this very different climate. From an archaeological point of view, this really is a game changer in how we try to understand or reconstruct the middle Holocene period.’
The full findings of the study were published in the journal Nature Communications.