Wednesday, January 03, 2007

 

Climate shift helped destroy China's Tang dynasty

The Tang dynasty*, seen by many historians as a glittering peak in China's history, was brought to its knees by shifts in the monsoon cycle, according to a study.

Famed for a flowering of art and literature and for prosperity brought by trade with India and the Middle East, the dynasty spanned nearly three centuries, from AD 618 to 907, before it was overwhelmed by revolt.

Scientists led by Gerald Haug of the Geoforschungszentrum (GFZ) in Potsdam, eastern Germany, looked at sedimentary cores taken from a lake at Zhanjiang in coastal southeastern China, opposite the tropical island of Hainan.

The magnetic properties and content of titanium in these deposits are an indicator of the strength of the winter cycle in the East Asian monsoon system, they believe.

They found that over the past 15,000 years, there had been three periods in which the winter monsoon was strong but the summer monsoon was weak.

The first two periods occurred at key moments during the last Ice Age, while the last ran from around 700 to 900. Each of these monsoon shifts coincided with what was, relative to the climate epoch, unusually cold weather.

The twilight of the Tang began in 751, when the imperial army was defeated by Arabs.

But what eventually destroyed the dynasty were prolonged droughts and poor summer rains, which caused crop failure and stoked peasants' uprisings.

Continued at "Climate shift helped destroy China's Tang dynasty" [Change]

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Based on the journal Nature letter:

Influence of the intertropical convergence zone on the East Asian monsoon

Gergana Yancheva, Norbert R. Nowaczyk, Jens Mingram, Peter Dulski, Georg Schettler, Jorg F. W. Negendank, Jiaqi Liu, Daniel M. Sigman, Larry C. Peterson and Gerald H. Haug

Nature 445, 74-77 (4 January 2007) | doi:10.1038/nature05431; Received 27 January 2006; Accepted 6 November 2006

Opening Paragraph

The Asian-Australian monsoon is an important component of the Earth's climate system that influences the societal and economic activity of roughly half the world's population. The past strength of the rain-bearing East Asian summer monsoon can be reconstructed with archives such as cave deposits but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct. Here we present high-resolution records of the magnetic properties and the titanium content of the sediments of Lake Huguang Maar in coastal southeast China over the past 16,000 years, which we use as proxies for the strength of the winter monsoon winds. We find evidence for stronger winter monsoon winds before the Bolling-Allerod warming, during the Younger Dryas episode and during the middle and late Holocene, when cave stalagmites suggest weaker summer monsoons. We conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone. Similar migrations of the intertropical convergence zone have been observed in Central America for the period ad 700 to 900 suggesting global climatic changes at that time. From the coincidence in timing, we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the Tang dynasty in China and the Classic Maya in Central America.

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*Info on the Tang Dynasty:

...Near the end of the Tang Dynasty, regional military governors took advantage of their increasing power and began to function more like independent regimes on their own right. At the same time, natural causes such as droughts and famine due to internal corruptions and incompetent emperors contributed to the rise of a series of rebellions. The Huang Chao rebellion of the 9th century, which resulted in the sacking of both Chang'an and Luoyang was the most destructive and took over 10 years to suppress. Although the rebellion was defeated by the Tang, it never really recovered from that crucial blow, weakening it for the future military powers to take over. In 907, after almost 300 years in power, the dynasty was ended when one of the military governors, Zhu Wen, deposed the last emperor and took the throne for himself which thereby inaugurated the Five Dynasties and Ten Kingdoms Period...

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