Cool periods in China, and the resulting scarcity of resources, are closely linked with a higher frequency of wars over the past 1000 years, according to Chinese researchers.

The research, which compared variations in climate with data from 899 wars in eastern China between 1000 and 1911, was published earlier this month (9 July) in the journal Human Ecology.

The finding that resource scarcity and shrinking agricultural output caused by changes in temperature is a major driver for war also applies to current society, says David Zhang, lead author from the Department of Geography at the University of Hong Kong.

Although Zhang did not analyse any warming periods, he believes extreme climate events ― both cold and hot ― could have a disastrous effect on the earth's ecosystem.

"It is more apparent that colder temperature would cause less crop production. However the ecosystem and agricultural production, once adapted to lower temperature, would surely be disturbed in a higher temperature today," he said.

Zhang believes that changes in ecosystems could lead to social, economic and political change, and could spark off wars. Historically, warfare has been a way of redistributing resources in response to climate change.

Wang Shaowu, from Peking University's Department of Atmospheric Physics, agreed that climate changes played an important role in the switch of dynasties and social revolutions in Chinese history.

He noted that drought and less precipitation, which do not always coincide with cold periods, were also significant factors affecting the agricultural production in countries like China.

According to Zhang, the finding also applies to ancient agricultural societies in other countries. For example, when the Ming dynasty (1368-1644) collapsed, other populated areas like Europe, Japan, Korea and the Ottoman Empire were also experiencing the most turbulent time in their history.

But according to An Chengbang, a research fellow with the Institute of Geography of Lanzhou University, both warming and cooling are long-term trends and the meteorological data collected during the past decades are not enough to accurately predict how global warming might influence agriculture.

Zhang also said in a "well-organized" society like today, we may not resort to warfare in the face of climate change, but instead may come up with more positive solutions.

"[We] may resort to technological development to increase the production," says Zhang.

Zhang said he will publish more findings on a global scale by the end of this year.

Reference: Human Ecology doi 10.1007/s10745-007-9115-8 (2007)