Scientists hope the new discovery will better help forecast the arrival of El Nino events, which usually bring dry, hot conditions to parts of Australia (REUTERS: Mick Tsikas)
Tell-tale signs that an El Niño climate event is looming are detectable up to 18 months beforehand, scientists have found, nine months earlier than current models can predict.
Early warning of these events, which usually bring dry, hot conditions to much of Australia, would be welcome news for the country’s farmers, fire fighters and weather forecasters.
The vital clues lie beneath the surface of the Pacific Ocean north of Australia, say climate scientists Nandini Ramesh and Raghu Murtugudde in the journal Nature Climate Change.
El Niño events appear when waters in the tropical eastern Pacific start to warm up, resulting in cooler oceans near Australia with less clouds and reduced rainfall. Scientists have struggled to understand the early steps in this process.
Ramesh, who is currently based at the University of New South Wales’sClimate Change Research Centre, studied El Niño events from 1958 until 2011 to try to identify climate factors that were present during all of them.
She found that although not all El Niño events follow the same course, they all begin with a discharge of massive volumes of sub-surface warm water from the equatorial western Pacific.
“This is an important discovery,” saysProfessor Matthew England from the Climate Change Research Centre. “Improving our skill at predicting El Niño events is one of the holy grails of climate research. This research should significantly improve our ability to forecast El Niño events.”
This sub-surface process had not been noticed before because the discharge of warm water is not easy to detect using satellite measurements.
“When we looked below the surface, there was this big blob of warm water that was there far before anything was visible on the surface,” says Ramesh, who is a pre-PhD student.
The discharge always begins during the winter or spring of the year before an El Niño event, up to 18 months before the peak, she says.
“El Niño events usually peak in December or January, and right now our best predictions start in March to May of the same year … but the process we have discovered starts in June or July of the year before,” Ramesh says.
“We hope that this will enhance our ability to predict El Niño so that communities can begin preparing for their effects much earlier.”
The findings also reinforce the scientific value of systems for observing the ocean, says England.
“We need to maintain the observational programs that measure interior ocean water properties. These measurements are vital for understanding ocean circulation, climate, sea-level rise, and marine ecosystems.”
Author: Stephen Pincock