published on 15 April 2007 in air

Climate and dynasties

Scientific research
Far worse than Attila the Hun, the true calamity that has led to the fall of flourishing civilizations is climate change. And now it is back again, in the most unnatural ways. Historically entire civilizations, like that of the Fertile Crescent or the Mayas, disappeared because of climate changes which reduced the production of food, provoking a reversal in social hierarchies. Something similar also seems to have occurred in China where the onset of climate changes seems to have coincided with the fall of some of the dynasties that reigned over the Middle Kingdom. This is what has been stated in a research carried out by scientists of the University of Minnesota and of the Lanshou University in China, published on the magazine Science.
In order to come to this conclusion, the group of researchers, directed by the chemist Hai Cheng, analysed the isotope composition  of a 12 cm. stalagmite, taken from a cave in the North of China,  which started to form in 190 A.D., and continued to grow up to 2003, when it was collected.
By  analysing the uranium and thorium  isotopes   it was possible to date every layer of the stalagmite very precisely, while the comparison of the abundance of oxygen in the two isotopes enabled the reconstruction  of the temperature and rainfall in that stretch of time. It was noted that at the end of the Tang, Yuan and  Ming dynasties, periods that were well known for widespread disorders of the people,  the summer monsoon was milder than the normal standard, which brought China much less rain than the average amount, which therefore probably provoked a drastic decrease in the rice harvests, and therefore severe famines. On the contrary, the Chinese Golden Age, during the period of the Song dynasty, coincides with a marked increase in the rainfall that must have doubled the rice harvests and thus enabled a rapid increase in the population.

The fall of the dynasties
The most interesting aspect of this research is that  what took place in China in those times, coincided with analogous events on the other side of the world, which shows that these sudden climate changes took place on a planetary scale. The fall of the Tang dynasty, around the year 900 A.D.  coincided with the analogous fall of the Maya civilization in Central America, which was also provoked by a period of draught. The Golden Age of the Song dynasty instead, corresponds to the “Medieval Warm Period” when, around the year 1000, the Vikings spread out and colonized the southern part of Greenland.
The cooler climate that followed in the 15th century, not only brought about the disappearance of the Viking colonies from Greenland, but in China it provoked a famine and the end of  the Yuan dynasty. Lastly the fall of the Ming dynasty in the 17th century took place  right in the middle of the Little Ice Age which had gripped Europe. This research must make us reflect whether climate changes, including the current one, are natural events where human influence does not affect the climate. No. The research carried out by Hai and his colleagues shows  that a stronger summer monsoon and the consequent increase in rainfall in the past, took place in the periods of global warming. Today the temperatures are rising, but the  Northern part of China is becoming increasingly arid, which shows that the present climate change is anomalous, provoked by  causes, such as the accumulation of CO2 in the atmosphere, unlike those of the past.

Edited by Videoscienza

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