A new study has revealed a stronger evidence for the climate-conflict link, with data showing that tropical countries affected by the El Niño-Southern Oscillation are twice as likely to suffer internal unrest compared to the phenomenon's cooler, wetter counterpart, La Niña.

Between 1950 and 2004, the risk of civil wars doubled in 90 tropical countries when hit by El Nino, according to the study published in Wednesday's Nature, by scientists from Princeton University and Columbia University's Earth Institute.

The study gives hope to the future of humanity, given the fact that El Nino patterns can be predicted up to two years ahead. If the correlation does exist, pre-emptive action can be taken for some conflicts and reduce humanitarian suffering. 

The scientists correlated ENSO from 1950 to 2004 with onsets of civil conflicts that killed more than 25 people in a given year. The data included 175 countries and 234 conflicts.

The study concluded that in countries whose weather cycles are determined by ENSO, the risk of civil conflict occurring during La Niña was about 3 per cent; during El Niño, this doubled to 6 per cent, while in contrast, countries not affected by ENSO remained at a stable 2 per cent.

According to the study, El Niño may have played a role in 21 per cent of civil wars worldwide, with 30 per cent in those countries  being directly affected by El Niño.

Remarkable links were found between El Nino patterns and civil unrest in Peru in 1982 and Sudan in 1963.

Further, a strong link between violence and El Nino were also found in El Salvador, the Philippines and Uganda in 1972; Angola, Haiti and Myanmar in 1991, and Congo, Eritrea, Indonesia and Rwanda in 1997.

What it does show and show beyond any doubt is that even in this modern world, climate variations have an impact on the propensity of people to fight, says Mark Cane, a climate scientist at the Lamont-Doherty Earth Observatory at Columbia University in New York.

It's difficult to see why that won't carry over to a world that's disrupted by global warming.

El Nino brings high temperature and more scarce rainfall every three to seven years, impacting weather patterns across much of Africa, the Mideast, India, southeast Asia, Australia, and the Americas, which holds half the world's population. 

Interacting with other factors including wind and temperature cycles over the other oceans, El Nino can vary dramatically in power and length. At its most intense, it brings scorching heat and multi-year droughts. 

This is the first major evidence that the global climate is a major factor in organized violence around the world, says Solomon M. Hsiang, the study's lead author, a graduate of the Earth Institute's Ph.D. in sustainable development.

While the study does not blame specific wars on El Nino, it confirms many scientists' speculation over the strong link between climate-conflict.

Just this July, the UN Security Council discussed on climate-driven conflicts. Secretary-General Ban Ki-moon noted that the possible adverse effects of climate change are not only exacerbates threats to international peace and security; it is a threat to international peace and security.

The most important thing is that this looks at modern times, and it's done on a global scale, said Hsiang. We can speculate that a long-ago Egyptian dynasty was overthrown during a drought. That's a specific time and place, that may be very different from today, so people might say, 'OK, we're immune to that now.' This study shows a systematic pattern of global climate affecting conflict, and shows it right now.

No one should take this to say that climate is our fate. Rather, this is compelling evidence that it has a measurable influence on how much people fight overall, said the co-author Mark Cane, a climate scientist at Columbia's Lamont-Doherty Earth Observatory.

Sudden climate cycle changes often also caused loss of crops, hurricanes damage; increases the spread of epidemics such as water-borne disease, amplifies hunger, loss, unemployment and inequality, which fuels division and tear the communities apart.

Even though we control for all of these factors simultaneously, we still find that there's a large and pervasive El Niño effect on civil conflicts, Hsiang said in a teleconference.

Speaking of the current crisis in the Horn of Africa, Hsiang said it was a perfect example of the hidden damages of an El Niño.

Forecasters two years ago predicted that there would be a famine in Somalia this year, but donors in the international aid community did not take that forecast seriously, says Hsiang.

We hope our study can provide the international community and governments and aid organisations with additional information that might in the future help avert humanitarian crises that are associated with conflict.