Collapse Of Civilisations Linked To Monsoon Changes
Collapse Of Civilisations Linked To Monsoon Changes
New Scientist ^ | 1-4-2007 | Catherine Brahic
Collapse of civilisations linked to monsoon changes
11:13 04 January 2007
NewScientist.com news service
Catherine Brahic
The downfall of the one of the greatest Chinese dynasties may have been catalysed by severe changes in climate. The same climate changes may have simultaneously led to the end of the Maya civilisation depicted in Mel Gibson's new film Apocalypto.
So says Gerald Haug of the GeoForschungsZentrum in Germany and colleagues, who studied geological records of monsoons over the past 16,000 years. They have found a startling correlation between climate extremes and the fall of two great civilisations: the Tang dynasty in China and the Maya of South America. “It blew me away," says Haug.
The records show that around the time that these civilizations went into decline, they experienced stronger than average winds in the winter and weaker summer monsoon rains. These weak rains would have reduced crop yields.
Records of monsoons beyond the last 50 years are difficult to obtain. Looking for signs of monsoon trends in geological records going back thousands of years can help solve this problem. In China, stalagmites provide the best available historical record of summer monsoon rains, says Haug, as more rain increases the amount of water dripping down from the roofs of caves. But until now, there has been no reliable estimate of winter winds.
Iron and titanium
Haug and his colleagues solved this problem by studying the sediments deposited at the bottom of Lake Hugauang Maar in southeastern China. The sediments are made up primarily of material deposited there by winter monsoon winds because the catchment area is small, meaning very few streams bring in sediments from other sources. As a result, the sediments provide an accurate historical record of the strength of the winter monsoon winds.
(Excerpt) Read more at environment.newscientist.com ...
