Throughout
centuries, the fortunes of China's
ancient kingdoms rose and fell with monsoon cycles, a new study suggests.
The
discovery is based on a nearly 2,000-year-old record of monsoon activity
recently discovered in a cave.
Monsoon
winds
carry rain-laden clouds through
When
the winds are weak, little to no rain reaches large expanses of
The new
study "is a brilliant analysis of the problematic coincidence of abrupt
climate changes and changes in political organization," said Harvey Weiss,
an archaeologist at
"Really
Surprised"
In the
Wanxiang cave
in north-central
The
rock had been growing continuously for 1,800 years, from A.D. 190 to 2003.
Like
trees, stalagmites have annual growth rings that can provide clues about local
environmental conditions for a particular year.
The
team measured the amount of oxygen-18—a rare form of "heavy"
oxygen—in the stalagmite growth rings. Growth rings with large amounts of
oxygen-18 indicate years of weak summer monsoons and less rains.
Comparing
the stalagmite record with Chinese history, the researchers found that a period
of strong monsoons was associated with the "golden age" of the
Northern Song dynasty.
During
that time, improved rice yields allowed the population to increase from 60
million to as many as 120 million.
"I
was really surprised," said study co-author Hai Cheng, a geologist at the
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
(Read
about the brilliant,
cruel emperors of the Han Dynasty in National Geographic magazine.)
"Compelling"
Peter
deMenocal is a paleoclimatologist at
"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
Scientists
have linked droughts plaguing large swaths of modern
"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,"
"In
their time, these ancient cultures were in many ways just as impressive as
modern societies."
In north-central
Monsoon cycles coincide with the rise and fall of
Image courtesy Science/AAAS
http://news.nationalgeographic.com/news/2008/11/081106-monsoons-china.html
Courtesy:
National Geographic News
November 6, 2008