Researchers say that when 500-year-long sun cycles brought warmth, communities flourished, but when the Earth cooled, ancient societies collapsed.
Scientists say they have found evidence beneath a lake in northeastern China that ties climate change and 500-year
to ups and downs in the 8,000 years of Chinese civilisation.
According to the study by a team at the Institute of Geology and Geophysics in Beijing published in the science journal Nature Communications this month, whenever the climate warmed, Chinese civilisation prospered and when it cooled, it declined.
While historians have used various social and economic factors to explain changes over the millennia, Dr Xu Deke, lead author of the paper, and his colleagues said that while people played their part, their study indicated that cycles in solar activity influenced human activity.
“We just point out there is a natural constraint on human efforts,” Xu said.
For this latest study, the team and its leader, Chinese Academy of Sciences professor Lu Houyuan, took plant and lake bed sediment samples to track climate change over the centuries and compared them with written records.
They visited Lake Xiaolongwan in the Changbai Mountains in Jilin province and studied the spread of plant life such as oak trees to map the transitions between warm and cold climate phases in northern China.
Whenever that happened, societies started to collapse and neither culture nor political systems could sustain them. This, Xu said, was a lesson for modern China.
“The most effective countermeasure is science and technology,” he said. “We are in a much more capable position than our ancestors with the help of technology and machines in face of global cooling, but preparation must start now.”
Citing this and earlier studies, Xu said that over the next few decades the Earth would enter 25 years of cooling, although greenhouse gases could slow the temperature drop.
Cooling would increase the size of polar ice caps and lower sea levels. Areas such as southern China could benefit as land would be reclaimed from the sea.
But overall, a cooling climate would continue to have a more negative effect on civilisation than warming, Xu said.
Dr Liu Yonggang, a Peking University scientist who studies ancient climate, said the researchers had provided important new information and perspectives.
Human societies have gone through temperature cycles such as the Medieval Warm Period (900- 1300) and Little Ice Age (1300-1870) Liu said, but most of that data came from Europe, not China.
The study left one big question. “Why do the sun’s activities vary every 500 years? Nobody can explain,” he said.
“We need to know more about the inner working mechanism of the sun, otherwise the future remains unpredictable.”