Looking at the rings within a centuries-old tree, researchers now know that the fall of the Angkor Empire nearly 600 years ago came shortly after a “sustained mega-drought”. In a new study, scientists link the ancient Kingdom’s collapse to similar events across the globe and throughout history, drawing parallels between high temperatures, heavy rain and drought with human conflict and violence.

University of California professor Solomon Hsiang, the lead author of the study released Thursday in Science, and his team spent the last 18 months looking into past climate changes across the globe and what major events occurred simultaneously with those shifts in the climate.

“What was lacking was a clear picture of what this body of research as a whole was telling us,” Hsiang said.

The study, focusing on negative aspects of society such as civil conflict, ethnic violence, rape, political riots and the collapse of entire civilisations from ancient times to present day, draws the conclusion that as temperatures and occurrences of drought rise, so does human violence both interpersonally and in groups.

An example included within the study looks at Hindu-Muslim riots, which are seen normally following intense rainfall.

“This relationship between intergroup violence and rainfall is primarily documented in low-income settings, suggesting that reduced agricultural production may be an important mediating mechanism – although alternative explanations cannot be excluded,” notes the study.

The researchers also call upon psychological research in which subjects often take on aggressive or violent behaviour if controlled temperatures are higher.

Tin Ponlok, deputy director general at the Ministry of Environment’s climate change office, said he had not seen the study but was not surprised by its findings.

“It’s quite natural to expect that climate change would cause social change such as the social economy, environment, etc. With changes like that, we should expect support from the conclusion,” Ponlok said.