The Tibetan Empire, once the highest elevation empire in the world, flourished from 618 to 877 CE in the challenging conditions of the Tibetan Plateau. With its population of 10 million people spread across a vast area of East and Central Asia, including parts of northern India, it is remarkable that the empire thrived in such hostile conditions. However, its collapse in the 9th century remains a puzzle. New research published in Quaternary Science Reviews seeks to shed light on the potential influence of climate on the demise of this great civilization.
In order to understand the environmental changes that occurred 12 centuries ago, researchers turned to the study of lake sediments, known as paleolimnology. By analyzing the sediments of Xardai Co, a freshwater lake, the research team uncovered valuable clues about the past. They focused specifically on the diatoms, microscopic algae that leave behind fossils in the sediment layers. The scientists observed a significant shift in the types of diatoms present in the sediments, indicating a transition to drier conditions and lower lake levels.
The study revealed a consistent pattern of high lake levels during the period of the Tibetan Empire’s rise and peak, circa 600-800 CE. This suggests warm and humid conditions prevailed during this time. However, as the empire reached its zenith, the climate shifted dramatically, leading to severe drought from 800 to 877 CE. The researchers argue that this prolonged drought likely resulted in crop failure, triggering social unrest, and exacerbating religious and political challenges that eventually led to the downfall of the empire.
The Tibetan Plateau is highly sensitive to changes in climate due to its high elevation. The region experiences significant variations in temperature and precipitation compared to the global average. Xardai Co, the study lake, is typically covered in ice from November to April and experiences temperature fluctuations between -12.1°C and 14.1°C, as well as an annual rainfall of 71mm. These climate factors have a direct impact on lake levels and the organisms that inhabit them.
The core samples extracted from Xardai Co’s sediment provided valuable insights into the diatom assemblages present. The study identified a total of 160 diatom taxa, with only 23 considered significantly abundant. Prior to 800 CE, the dominant diatoms were Lindavia radiosa, Lindavia ocellata, Amphora pediculus, and Amphora inariensis. The ratio of planktonic to benthic diatoms peaked during this period of wet and humid conditions with elevated lake levels.
At the tipping point of 800 CE, there was a rapid increase in benthic diatoms, specifically Amphora pediculus and Amphora inariensis, while the previously dominant open water diatoms declined. This shift in the diatom community persisted until 1300 CE, marking the beginning of the Little Ice Age when lake levels started rising again. The findings from Xardai Co were corroborated by other paleoenvironmental indicators, including precipitation records from Banggong Co and temperature records from China, indicating that these climate changes were not localized but widespread across the Tibetan Plateau.
During the height of the Tibetan Empire, agriculture and livestock farming were the primary livelihoods. The warm and rainy climate would have facilitated crop production in the Yarlung Zangbo River valley and provided ample pasture for grazing animals on the Qangtang Plateau. The favorable conditions also allowed for the cultivation of crops at higher altitudes. Horses, goats, and yaks played a crucial role in the trade economy of Tibet.
However, the sudden and significant decline in climate over a span of approximately 60-70 years would have severely impacted plant growth, resulting in reduced agriculture and pastoral grazing. This would have led to food shortages and hindered the economic prosperity of a trade-reliant empire. The ensuing social unrest fragmented the empire, with different political agendas further contributing to its ultimate demise.
Today, agriculture and pastoral activities remain vital to Tibet’s economy. Consequently, understanding the toll climate takes on communities in inhospitable environments is of paramount importance. By studying the collapse of the Tibetan Empire, we can learn valuable lessons about the interplay between climate, livelihoods, and societal resilience, ensuring that these communities not only survive but thrive in the face of climate challenges.
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