The team found that when China was ruled by its final imperial dynasty, a general cooling of the climate induced long-term fluctuations in the economy. It also discovered that the population acted primarily as consumers rather than producers, leaving it all the more vulnerable to these economic fluctuations.

"To improve current plans of adaptation or mitigation, we need to know about these past interactions between climate change and human societies," said Qing Pei of the Education University of Hong Kong. "Economy is usually the pillar of a society. Therefore, lessons on climate change and the economy could be [beneficial in understanding] the future of human beings when facing unprecedented global warming."

In recent decades, climate change has been associated with an overall global warming, although this has not always been so. Between the 16th and 19th centuries, much of the world underwent a period of modest cooling, which has come to be known as the "Little Ice Age". It has been reported that, in southern China, farmers ceased to grow certain warm-weather crops such as oranges during this period.

"In terms of past agrarian society, cooling is more harmful," said Pei. "The agrarian society needs more thermal energy to maintain the growth of crops and other kinds of agricultural products."

Together with Harry Lee at the University of Hong Kong and colleagues, Pei investigated how the Little Ice Age affected the economy of late-imperialist China. The researchers collated climate and socio-economic data and performed statistical analyses to assess links between the two.

They found that climate change – particularly temperature rather than precipitation – inflicted long-term economic fluctuations on the country. What's more, in contrast to early modern Europeans, China's population tended to consume more than it produced, meaning that it was less well equipped to weather those economic fluctuations.

"In the long term, the population mainly acted as consumers, which means the increase of their consumption rate was faster than the increase of [their] production rate," said Pei. "Therefore, they may have suffered more to maintain sources of food for their survival, especially under climate change, which would have further shrunk the land carrying capacity."

Pei believes that scientists and policy makers could reflect on these findings when considering how to deal with today's climate change, although he warned that effects will not be totally the same. Different regions may be inherently more or less vulnerable to economic impacts from climate change, he said, especially because of the size and type of population – big or small, consumer or producer.

The researchers – who claim that their study also has implications for general socio-economic ideas such as Malthusian theory and Great Divergence theory – would now like to perform similar studies on smaller spatial and temporal scales.

"In the near future, we are going to downscale and contextualize the influence of climate change on human societies," said Pei. "In the meantime, we will try to include more physical and social-economic factors in our quantitative analysis to explain the empirical past of China in relation to climate change."

The study is published in Environmental Research Letters (ERL).

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