Researchers reported on Wednesday that the El Nino climate cycle doubles the risk of civil wars in tropical countries.
El Nino spreads warm, dry air around the globe every four years or so.
Scientists from the Earth Institute at Columbia University reported in the journal Nature that one out of every five civil conflicts were influenced by El Nino between 1950 and 2004.
It is the first study to quantify the link between El Nino, droughts that follow it and upheaval in countries that bear the brunt, Reuters reports.
The researchers found Peru in 1982 and Sudan in 1963, 1976 and 1983 showed remarkable links between El Nino patterns and civil unrest.
Other countries with a strong link between trouble and El Nino include El Salvador, the Philippines and Uganda in 1972; Angola, Haiti and Myanmar in 1991 and Congo, Eritrea, Indonesia and Rwanda in 1997.
The researchers focused on internal civil conflicts because these account for 80% to 90% of all conflicts since 1950.
Some 40% of the conflicts that occurred would probably have happened anyway, but the stresses of El Nino made conflict more likely, and sometimes made it happen earlier.
The scientists said poorer countries were at the greatest risk.