As the world begins 12 days of intense discussion in Copenhagen, Denmark, about how to combat climate change, the debate in China is about whether global warming is good or bad for China. If 3,600 years of history is anything to go by, Chinese civilisation has flourished when temperatures have been at their warmest and declined when the climate cooled. It is a relationship that could hold lessons for today, says Professor Xie Zhenghui , deputy director of the Chinese Academy of Sciences' International Centre for Climate and Environmental Sciences. Ask the scientists and some will warn the growing season for farmers will become shorter, the weather more extreme and sea levels higher. Moreover, they say China, as the biggest emitter of the greenhouse gases that cause warming, risks being blamed by other countries for disasters around the world. Others see potential benefits. More carbon dioxide in the atmosphere would accelerate the growth of crops, higher temperatures would open up for cultivation land in northern areas such as Inner Mongolia that are too cold to grow crops today, warmer air over the oceans would bring more rain to China's drought-plagued interior and the frequency of extreme weather would eventually decrease once temperatures stabilised, they say. 'Chinese historical records show that the temperature would stabilise after a sharp climb. Mother Earth has a lot of mechanisms to adjust herself to a new equilibrium,' Xie said. 'In my opinion, the sooner the temperature increases the better. The longer it takes, the more extreme weather we will have to face. Extreme weather is the hallmark of transitional periods. Once we enter the warm and stable periods like those in the Han and Tang dynasties, we will be fine.' As this division of opinion suggests, predicting the future may be beyond contemporary climate science. But the past may indeed hold lessons. For thousands of years, Chinese scholars have kept precise and meticulous meteorological records; such information was crucial for the government to plan and guide agricultural production. (China has the longest continuous recorded history of any civilisation.) Everything was archived, from the date each year that ice began forming at the mouth of the Yellow River to the flowering and seeding patterns of certain plants. The data allows scientists today to chart a reliable pattern of climate change in China over three and a half millenniums. From the prosperity of the Shang dynasty 3,600 years ago to the ruin of the Bronze Age, the cultural peak of the Tang dynasty in the seventh to 10th centuries and the subsequent ravages wrought by horsemen from the north, Chinese civilisation has reached its highest points when temperatures have been warmest and its lowest points when they have cooled. Wang Zijin , an environmental historian at Beijing Normal University, said the relationship between temperature and success was no coincidence. When the weather cooled, agricultural output fell, wealth contracted, discontent rose and China became more vulnerable to invasion from the north. 'In the long term, warming may not be a curse but a blessing [to China],' he said. 'According to what happened in the past, if the temperature continues to rise in the future we may not see the return of elephants, but it will be very possible that rice and bamboo can again grow along the Yellow River. Xinjiang , Gansu and Inner Mongolia will become much more habitable than they are today.' This relationship between temperature and dynastic potency was first drawn by a meteorologist named Zhu Kezhen in a 1972 paper. Zhu was one of the first Chinese PhD graduates of Harvard University and helped lay the foundations of modern meteorology on the mainland. In his paper, the last he wrote and considered a classic for its elegant prose and bold conclusions, Zhu drew a graph plotting temperatures in the Yellow River region from 1500BC to 1950. Based on archaeological artefacts and historical documents, the graph charted the rises and falls in temperature. It showed that there were three extended periods of warm temperatures. The first coincided with the Shang dynasty (1600BC-1046BC), when the annual average temperature reached as high as 11.3 degrees Celsius. This period saw the emergence of the first comprehensive set of Chinese characters, massive construction of palaces and cities, large-scale farming and the production of systematic astronomical records and sophisticated bronze wares. The second extended period of warm temperatures lasted more than 700 years, from the Eastern Zhou dynasty (770BC-256BC) to the Western Han dynasty (206BC-9AD), when average temperatures peaked at 10.7 degrees Celsius. In the Eastern Zhou, China's territory expanded from the Yellow River to Guangdong, Yunnan and Sichuan. There was an enormous bamboo forest along the Yellow River, while the Yangtze River cut through lush rainforest. Slavery was abandoned, iron tools became popular in farming, and Confucius and other scholars established the philosophies that shape Chinese society today. By the time temperatures started to dip, China had built the Great Wall, a national network of roads and conquered Xinjiang, Vietnam, Taiwan and Korea. A third warm period, when average temperatures peaked at 10.3 degrees, coincided with the Tang dynasty, widely seen as the peak of Chinese civilisation. Some historians estimated China accounted for 60 per cent of global gross domestic product during this era. From textiles, ceramics, mining and shipbuilding to paper making, China led the world in almost every sphere. There was also a spiritual and cultural boom - there were more poets in the Tang than at any time in history. In between these great dynasties, average temperatures plunged and chaos reigned. The Chinese empire retreated, and was even driven into the sea by the invading Mongols who established the Yuan dynasty (1271-1368). The longest period of relative cold lasted from the end of the Tang to the fall of the Qing dynasty in 1911. Now temperatures are on the rise again, matched by scorching economic growth. According to the Yellow River Conservancy Commission, the average annual temperature was 10.3 Celsius from 2001 to 2007 - the same as in the Tang dynasty. Zhu's research was based on records which make for interesting comparisons with the present day. Rice could be harvested twice a year to the north of the Yellow River in the Eastern Zhou dynasty, whereas the region is generally dry now. Plum trees were common along the Yellow River in the Tang dynasty, but since then have only grown further south. Xu Ming, chief author of a study by global environmental group WWF on the impact of climate change in the Yangtze River region, said China should focus less on prevention and more on mitigation. Instead of ploughing money into expensive carbon reduction technologies, it should build more water redistribution facilities, plant trees and develop new crops that could endure temperature fluctuations. 'China should do something within its limited capacity to reduce greenhouse gas emissions, but no matter what we do, global warming is inevitable. Therefore we must get ready for it,' said Xu, a professor at the Institute of Geographic Sciences and Natural Resources Research under the Chinese Academy of Sciences. He said a rise in sea levels would pose a long-term threat to coastal cities including Shanghai, which could end up below sea level and needing protection by dykes. 'Adaptation requires a tremendous amount of money, resources and advanced technology. China is far from ready. Our citizens are complaining about uncommon icy rains, droughts and snowstorms. They count on the government for protection.'