PRESS ASSOCIATION -- Wars and civil conflict are more likely to happen when people feel the heat, a study has shown.
A naturally recurring weather system that boosts temperatures in the tropics has doubled the risk of civil war in 90 countries, research suggests.
El Nino, which occurs every three to seven years, may help account for a fifth of worldwide conflicts over the past 50 years, say experts.
The study is the first to demonstrate a direct link between climate events and recent conflict. Against a background of ongoing climate change, it raises the spectre of more turbulent times ahead.
Although the research does not address the issue of long-term climate change, scientists believe natural weather cycles will become more extreme as a result of global warming.
El Nino is one half of the Southern Oscillation, a see-saw weather system caused by changes in Pacific sea surface temperature.
It leads to warmer conditions and droughts across many tropical parts of the world including much of Africa, the Middle East, India, Southeast Asia, Australia and the Americas.
The other half of the cycle, known as La Nina, is marked by cooler conditions and more plentiful rainfall.
Scientists compared recorded Southern Oscillation data with the history of conflicts in the tropics from 1950 to 2004 that killed more than 25 people in a given year.
They showed that violent upheaval in 175 countries was twice as likely in El Nino years than in La Nina years. The study, published in the journal Nature, covered 234 conflicts, over half of which caused more than 1,000 battle-related deaths.