Climate change in recent years has fueled migration worldwide. Floods in Pakistan have forced millions from their homes, while the island nation of Kiribati’s entire existence is in doubt due to rising sea levels, according to NASA. A new study suggests that mass migration due to changing climates is not a new occurrence. The research explores the impact of droughts and floods in China between the years 800 and 907.
Writing in Communications Earth and Environment, a multinational research team detailed how these unusual weather patterns influenced political and social upheaval during this period, which was marked by the collapse of the previously dominant Tang dynasty.
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Reading Past Tree Ring Data
This dynasty ruled Imperial China from 618 to 907 and achieved remarkable social and political organization. The era was marked by complex administrative systems and a “golden age” of cosmopolitan culture that supported arts such as woodblock printing, poetry, and painting. They also allowed diverse religious freedom.
The authors focused on the hydrology of the Huanghe River (Yellow River) during this period. They analyzed climate proxy data from sources such as tree rings. These rings can indicate climate conditions over huge time spans. Each annual ring can tell researchers whether the year was dry or rainy, as wet years help trees grow faster and produce thicker rings.
The team gathered data from long-term tree-ring records from the area through which the Yellow River flows. Imperial China would have been dependent on a reliable flow of water through the Yellow River at this time.
“The runoff eventually reaches further downstream and influences the amount of water available, for example, for irrigating the fields,” said the study’s first author, Michael Kempf, a geographer at the University of Cambridge, in a statement.
A Changing Climate Could Have Led to Food Shortages
The team concluded from their analysis that an increase in the frequency of droughts and floods contributed to the eventual fall of the Tang dynasty.
“Hydroclimatic extremes have a very direct influence on crop failure and grain storage conditions,” said Kempf. The resulting food shortages were made worse by the empire’s choice of crops.
Citizens in the region had increasingly shifted from cultivating millet to wheat and rice. Although the reasons for this change are unclear, it meant that climate-resistant millet was replaced by more vulnerable crops. Wheat and rice require more water to grow than millet. Drier periods would have exacerbated food shortages, said Kempf. This increased the risk of famines during droughts.
The same weather events that impacted crop production in this region also disrupted supply routes into the region, making it difficult to replenish food stores.
The impact of these extreme weather events and the social pressures they generated may have weighed on soldiers who guarded the empire's borders against invading forces.
“Of course, people were weakened and therefore more vulnerable. Due to the military pressure on the outer border regions, they migrated south, where they believed they would find better conditions,” said Kempf. “This led to political destabilization and is likely to have contributed to the demise of the Tang dynasty.”
The dynasty eventually splintered into smaller kingdoms after the collapse. The study raises important points about how the weather shifts. In combination with social pressures, it can destabilize societies. As man-made climate change makes our weather more unpredictable, lessons from the past may help societies of today reckon with a less certain world.
Article Sources
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This article references information from a recent study published in Communications Earth and Environment: Hydroclimatic instability accelerated the socio-political decline of the Tang Dynasty in northern China
This article references information from NASA: NASA Sea Level Team Examines an Island Nation at Risk
