Climate change

Climate change linked to social unrest, HKU finds

PUBLISHED : Tuesday, 04 October, 2011, 12:00am
UPDATED : Tuesday, 04 October, 2011, 12:00am

Climate change that occurred hundreds of years ago may have been the underlying cause of social unrest in pre-industrial Europe, say researchers at the University of Hong Kong.

The researchers say cooler conditions from 1560 to 1660 resulted in shorter plant-growing seasons and reductions in arable land. Because of that, grain prices soared by 300 per cent, wars got longer and bloodier, and individuals became shorter.

'The average height of Europeans followed temperature closely and declined 2 centimetres in the late 16th century. It increased slowly with rising temperatures only after AD1650,' the researchers say in the new issue of the journal Proceedings of the National Academy of Sciences (PNAS).

The research team, headed by Professor David Zhang of the department of geography, claims to have established the first scientific verification of the causal link between cool climate and crisis. They looked at the history of Europe from 1500 to 1800, using records reflected in tree rings, and reconstructed the climate and socio-economic data during the period. That enabled them to compare temperature changes with grain price changes, population growth and war fatalities.

The research showed a strong link between grain production and temperature change. Prices tended to go up when temperatures went down.

'Many disturbances eventually developed into armed conflicts,' the article says. 'Although the number of wars decreased in the interval 1620 to 1650, these wars were comparatively more lethal and longer lasting. Annual war fatalities from 1620 to 1650 were more than 12 times those in the period 1500 to 1619,' it continued.

Zhang's team conducted a similar study in 2007 that showed climate change and armed conflicts and food and water shortage were related - but that study did not establish the cause-and-effect relationship.

Zhang said these new findings could fill the gap, thanks to recent advances in how geologists can reconstruct climatic temperatures at a given time or place.

The findings showed that Europe experienced a cool period during what now is called the Late Middle Ages - an era marked by calamities like the Black Death and upheavals.

And the Renaissance - which saw a boom in literature, science, art, religion and politics - took place during a relatively warmer period that spanned roughly the late 14th century to the early 17th century.

But just because bad things happened when the temperature went down in the past, good things would not necessarily happen if the earth's temperature rose in future, the researchers said.

'Although these historical periods of climate change featured lower temperatures, current rising global temperatures should not be viewed simply as a good sign,' Zhang warned.

Dr Harry Lee, a co-author of the research, said: 'Although we did not analyse any warming periods, that does not mean that warmer climate will not have a destablising effect. When higher temperatures are beyond a certain level, it can also spur human crisis. We shall need to collect more data.'

But he was quick to add: 'With advanced technology and improved social systems, like international relief systems, this destablising effect may be able to be delayed.'