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The Silk Road, the great patchwork of paths that connected the Atlantic seaboard of Europe with the Pacific coast of Asia, saw a change in its main route as a result of climate change, a study by Chinese scientists has found.
The main route, which usually went around the basin of the Tarim river, shifted northwards after the local climate changed. A few hundred years down the line, the climate changed again. But the route was still preferred due to geopolitical developments, which had the roots in the second change of climate.
The northward shift of the Silk Road is a valuable case study for examining the relationship between climate change and the spatial evolution of human societies, according to the researchers.
The Silk Road has an over 1,500-year-old history. While contacts between Europe and China are very old, the Silk Road — the flow of goods, animals, people, ideas, religions and disease between the opposite ends of Eurasia — is conventionally dated to the second century Before Common Era.
That is when Emperor Wu of the Chinese Han Dynasty dispatched his diplomat Zhang Qian to the ‘Western Regions’ (today’s Xinjiang and farther west). Han China was under threat from the Xiongnu, a powerful tribal confederation (who have been linked to the Huns who later terrorised Europe under Attila). Qian’s mission was to build relations with the Yuezhi and the Wusun, who Emperor Wu had learned were enemies of the Xiongnu. A branch of the Yuezhi would later form the Kushan Dynasty of North India, Pakistan and Afghanistan.
Qian travelled to the ‘Western Regions’ and is credited today as the ‘Father of the Silk Road’.
“The Tarim Basin route of the Silk Road was gradually established after the dispatch of Zhang Qian to the Western Regions (a historical name referring to arid NW China), in the 2nd century BCE by Emperor Wu of the Chinese Han Dynasty,” the researchers wrote.
In the centuries to come, caravans travelling from China’s capital of Xian or moving towards it used this route, which skirted the Tarim Basin. The Basin is enclosed by the Tianshan mountains to the north, the Kunlun mountains to the south and the Pamirs to the west. Within the Basin lies the Takla Makan Desert.
Having travelled around the Basin, the caravans travelled west till they reached the Levant (Today’s Syria, Jordan, the Holy Land and Lebanon) and Anatolia, where the goods would be transferred to ships moored in Mediterranean ports. The ships took them further west to Western Europe.
During ∼420–850 CE, the caravans no longer skirted the Tarim Basin. Instead, they began to use the northern slopes of the Tianshan — in an area known as the Junggar Basin in the northern part of today’s Xinjiang. This place was historically known as Dzungaria.
“Several hundred years later, the New Northern (NN) route (i.e., the Junggar Basin route) along the northern slopes of the Tianshan Mountains was established and was regarded as a replacement for the TB route. The rise of the NN route of the SR promoted the development of the Turco-Sogdian Milieux, connected the Chinese dynasties and nomadic regimes in Central and West Asia (e.g., the Khazar Empire), and facilitated communications and commerce from the Pacific to the Atlantic,” the researchers wrote.
But why did this happen? The answer, as per the researchers, was climate change.
In order to test their hypothesis, the researchers wanted to find variations in temperature and hydroclimate.
But there was a hitch. While hydroclimatic changes in the region had been intensively investigated using different archives, high-quality temperature records over the last two millennia were rare. Available records showed large discrepancies on centennial time scales over the period 1-1000 CE, according to the scientists.
The researchers then used a new method: insects.
Chironomids, commonly known as ‘lake flies’, are the most abundant insects in lake ecosystems. They have been successfully used to reconstruct paleotemperatures in temperate and arctic environments over the past few decades, due to the strong effects of temperature on all stages of their life cycle.
The researchers “obtained a precisely-dated, high-resolution chironomid-based temperature record” from Shuanghu Lake, which lies in the northern part of the Junggar Basin. It revealed temperature variations in this part of China over the last two millennia.
The scientists also carbon dated three sites, which used to be ancient cities during the heyday of the Silk Road: Shitoucheng (Tashkurgan today) and Gongzhubao on the Tajik-Chinese border and Tangchaodun, all located in Xinjiang.
The experts reasoned that besides environmental stresses, geopolitical conflicts may also effect changes in trade routes.
They thus compiled records of wars in the Tarim Basin from local chronicles, with the aim of distinguishing the potential role of climate change and geopolitical conflicts on the route shift of the Silk Road.
The results showed that during ~420-600 AD — a time of great turmoil in China known as the Northern and Southern Dynasties Period — temperatures in the study area reduced to such an extent that meltwater and precipitation greatly diminished.
The subsequent water shortage triggered the shift of the Silk Road route from the Tarim Basin to the northern slopes of the Tianshan mountains, where water resources were more abundant and stable.
From 600-850 CE, when the mighty Tangs ruled China, the climate again changed: This time, it became warm and wet.
Still, despite the availability of water, the northern route did not shift south. For just to the south of Xinjiang, Tibet had become an empire. The Tubo Kingdom or Tibetan Empire, known today especially for its ruler Songtsen Gompo, came into conflict with the Tang Empire.
“Interestingly, during the subsequent period of ~600 to 850 AD, the warm and wet climate did not prevent this shift, because of the geopolitical conflicts between the Tubo Kingdom and the Tang Dynasty in the Tarim Basin—the rise and expansion of the Tubo Kingdom were closely related to the relatively favorable climate on the Tibetan Plateau at that time. It thus reflects the indirect impact of climate change on the SR (Silk Road) shift,” wrote the researchers.
They added that their findings thus revealed “two distinct ways in which climate change drove the spatial evolution of human civilization, and they demonstrate the flexibility of societal responses to climate change”.
Climate change drove the route shift of the ancient Silk Road in two distinct ways has been published in the journal Science Bulletin.