Chinese and US scientists have uncovered prehistoric evidence of mass migration triggered by climate change.
Something occurred 4,200 years ago – a collapse of the monsoon system, the sapping of the groundwater, the sudden drainage of a lake – that brought a Neolithic culture to an end and left nothing but sandy landscapes in China’s Inner Mongolia region.
Archaeological evidence has revealed the jade carvings that once marked the Hongshan culture, along with evidence of hunting, fishing and even commercial traffic with Mongolian shepherds. And then the artefacts stop.
There is a 600-year period marked by no evidence of human settlement at all. Where there had once been streams, lakes grassland and forest, and a flourishing new Stone Age culture, only shifting sand dunes remained.
Recent origin
Xiaoping Yang, professor in the Institute of Geology and Geophysics at the Chinese Academy of Sciences, Beijing, and research colleagues from China, New Mexico, Hawaii and Texas report in the Proceedings of the National Academy of Sciences that they used a new laboratory technique to show that the northern Chinese deserts were not – as many had thought – millions of years old.
Instead, they are of very recent origin, and the researchers found evidence of dramatic change during human settlement.
In addition, the exploration of artefacts in the region – and the discovery, among other things, of a jade object that might be a dragon − now suggests that Chinese culture and identity may have its origins in the far north, rather than in the Yellow River basin, which has been the archaeologists’ working hypothesis until now.
If that was so, then one of the world’s great civilisations was founded by climate refugees.
Extraordinary claims require extraordinary evidence. The Beijing team used space-based radar topography measurements to show that the dunes and depressions of the Hunshandake region of northern China had once been home to lakes fed by a system of streams and rivers.
This was then confirmed with fossil evidence of tree pollens and algae that typically float in freshwater lakes.
The scientists built up a timetable of events by dating sediment samples with a technique called optically-stimulated luminescence, which reveals when minerals were last exposed to sunlight.
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This study has far-reaching implications for understanding how human populations respond and adapt to drastic climate change.
Steven Forman, geologist, Baylor University in Texas
They started with the proposition that an extraordinary series of droughts occurred in the northern hemisphere around 4,200 years ago, in North Africa, the Middle East and the Mediterranean.
Something similar happened in Hunshandake at around that time. The monsoon rainfall weakened, the lake levels dropped dramatically, and the water table was lowered drastically − and perhaps finally.
The researchers call it a “rapid and catastrophic shift”. And they warn that their research suggests that attempts to reverse the advance of the deserts in the region are likely to have limited success, because the change in the hydrological system is irreversible. Any water that fell there would just trickle away.
Human departure
Such discovery of links between climate and human departure is not isolated. In the last two years, meteorologists and archaeologists have identified climate change as a factor in the collapse of the Bronze Age Mediterranean culture, the implosion of the Assyrian empire at Nineveh in the 7th century BC, and the end of the Indus Valley civilisation 4,000 years ago.
Climate has also been implicated in the advance of the armies of Genghis Khan in the 13th century.
While climate change cannot explain everything about such shifts in ancient history, it is a factor.
But, say the Beijing scientists, “our evidence suggests that Hongshan culture was devastated by combined regional green/desert vegetation shift”, and that the change was intensified and made final by a sudden and final sapping of the groundwater table below the lakes and pastures in the region.
The scientist who used the optically-stimulated luminescence technique, geologist Steven Forman, of Baylor University in Texas, says: “This study has far-reaching implications for understanding how human populations respond and adapt to drastic climate change.”
