"I was really surprised," said study co-author Hai Cheng, a geologist at the University of Minnesota.
Furthermore, weak monsoon seasons coincided with droughts and the declines of the Tang, Yuan, and Ming dynasties.
Weak monsoons may have helped trigger one of the most tumultuous eras in Chinese history, called the Five Dynasties and Ten Kingdoms period, according to the study, detailed tomorrow in the journal Science.
During this time, five dynasties rose and fell within only a few decades, and China fractured into several independent nation-states.
(Read about the brilliant, cruel emperors of the Han Dynasty in National Geographic magazine.)
"Compelling"
Peter deMenocal is a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory in New York.
"The synchrony between these cultural events and climate change events is really compelling," deMenocal said.
DeMenocal's research has examined the role of climate change in the declines of ancient civilizations, including those of the Maya and Mesopotamians.
Throughout history, climate change has likely exacerbated already tense situations within empires caused by political upheavals or societal unrest, he said.
"Climate in many cases acts like the straw that broke the camel's back," deMenocal said.
Continuous Effect
The monsoon effect on China continues today, the study authors added.
Scientists have linked droughts plaguing large swaths of modern China to weakening monsoon winds during the past half century.
"The local government has sometimes had to move people out of some regions because they don't have enough water," said study co-author Cheng.
Monsoon variability in the past was driven by natural influences—such as changes in solar cycles and global temperatures. But today's waning monsoons are the results of human-driven greenhouse gas emissions, the new study suggests.
"I do think it's useful to look at this [study] as a lesson for our future," Columbia's deMenocal said.
"In their time, these ancient cultures were in many ways just as impressive as modern societies."
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