* El Nino events in Pacific can disrupt rainfall worldwide
* Predictions doubled from six to 12 months
* Could help farmers plant crops to withstand drought, flood
By Environment Correspondent Alister Doyle
OSLO, July 1 (Reuters) - Scientists have found a way to forecast El Nino weather events in the Pacific a year in advance, long enough to let farmers plant crops less vulnerable to global shifts in rainfall, a study showed on Monday.
While far from flawless, the technique doubles current six-month predictions of El Nino, a warming of the eastern Pacific linked in the past to floods in Peru and Ecuador, droughts in Australia and Indonesia and maybe severe winters in Europe.
"Better forecasting will mean farmers can adapt," Hans Joachim Schellnhuber, head of the Potsdam Institute for Climate Impact Research and a co-author of the report with experts in Russia, Israel, Germany and the United States, told Reuters.
El Ninos typically happen every two to seven years but scientists have been unable to find the causes of patterns that have occurred naturally throughout history and are among the most disruptive of extreme weather events.
The new system, built on a network of temperature records around the Pacific Ocean since 1950, correctly spotted El Nino events a year in advance more than half the time and gave false alarms fewer than one year in 10.
"We can develop a an efficient 12-month forecasting scheme, i.e. achieve some doubling of the early-warning period," the scientists wrote in the U.S. journal Proceedings of the National Academy of Sciences.
Even though the new computer-based system is not always right, farmers might find it worthwhile to invest in drought- or flood-resistant varieties of crops when there was a risk of an El Nino in a year's time.
"Six months' warning is too short. If you are a farmer in India, or in Zimbabwe or Brazil you have bought your seeds or even planted them. If you have a 12- or even 18-month early warning, you have a full agricultural cycle," Schellnhuber said.
Predictions of El Nino, part of a larger natural pattern known as El Nino Southern Oscillation, have often been unreliable. El Nino is Spanish for "the child", named after the baby Jesus because it often appeared off Peru around Christmas.
In September 2012, for instance, the World Meteorological Oganization saw a "moderately high likelihood" of an El Nino in the months ahead that did not materialise. It said last week that there were now "neutral" conditions in the Pacific.
A separate report, looking at evidence for El Nino events in the growth rings of more than 2,000 trees stretching back 700 years, suggested that climate change was the cause of a rise in the number of El Nino events in the late 20th century.
Writing in the journal Nature Climate Change, they also found that volcanic eruptions, which spew out particles that can affect sunlight, apparently affected El Nino cycles.
That was evidence, they argued, that heat-trapping gases from burning fossil fuels could similarly affect the cycle.
"We expect more strong El Ninos" overall this century because of rising concentrations of greenhouse gases, lead author Jinbao Li of the University of Hong Kong told Reuters.
(Editing by Alison Williams)