Researchers from the University of Hong Kong have found that extreme cold weather in the past centuries has coincided with wars, population collapse and economic crises. The ratio of wars in a cold climate was almost double the ratio of wars in a warm climate and periods of social turmoil over the centuries coincided with extreme weather, they found.
Geography professor David Zhang and researcher Harry Lee argued that global warming could have similar catastrophic effects on the world's population, triggering wars and social upheaval.
The study by Zhang and Lee, unveiled at a press briefing Wednesday, found that 80 percent of countries and areas around the world had a higher ratio of wars when weather was unusually cold.
Cool periods induced population collapses, with populations shrinking and fierce competition for limited resources, while in a milder climate, populations grow.
The scientists also found that during periods of unusually cold weather, socio-economic fluctuations were similar in Europe and China with increased economic and social problems.
"Global warming disturbs the eco-system and may bring humanitarian disasters," Zhang said, arguing that governments needed to prepare for the social effects as well as the environmental effects of climate change.
In the same way that extreme cold could lead to wars, continued global warming could result in a shortage of fresh water, land and food and subsequent conflicts and population shifts, Zhang warned.
The Hong Kong study is to be published in the Dec 4 issue of the prestigious US science journal Proceedings of the National Academy of Sciences (PNAS).