Sensitive equipment: maintaining the TAO array.
Floating sensors that have predicted extreme weather events for decades and saved lives in the process have been left to "collapse" amid vandalism and US budget cuts.
The United States and Japan set up the Tropical Pacific Observing System - made up of about 70 buoys - after a large El Nino event in 1982-83 caught forecasters unaware. Fourteen years later, the moored devices helped provide warnings of the “super” 1997-98 El Nino almost a year before it hit, probably saving lives and preventing billions of dollars in damage.
But the performance of the moored devices, which take atmospheric readings and monitor conditions down to 500 metres below the sea's surface, has fallen to about 40 per cent since 2012, according to the the climate observation director of the US National Oceanic and Atmospheric Administration, David Legler.
Satellite image of the most recent 'super' El Nino, taken in December 1997.
That is affecting the ability of forecasters and climate modellers, including those in Australia, to predict extreme weather patterns.
After operating at between 80-90 per cent capacity until about 2012, the performance of the system, also known as the TAO/TRITON array of buoys, dropped to “around 40 per cent” by the end of 2013, Dr Legler said.
The el Nino event in 2002-03, while considered to be a relatively weak one, had a big impact on Australia's rainfall.
"The collapse in the data return from the array has happened very rapidly,” head of CSIRO ocean-observing research Susan Wijffels said. “That has taken the community by surprise.”
The early alert before the 1997-98 event probably saved many lives and reduced the damage bill by billions of dollars, CSIRO principal research scientist Cai Wenju, who has published widely on El Nino events, said. Even so, he said, the event 16 years ago still killed 23,000 people as a result of weather events like drought and flood, and cost $45-50 billion in losses to global agricultural output.
El Nino events typically shift rainfall eastwards away from the western Pacific, bringing drought to eastern Australia. Countries on the eastern Pacific usually get heavy rainfall.
Warming sub-sea temperatures in the eastern Pacific are one sign an El Nino is on the way, Dr Cai said.
“Without that sub-surface information that we can put into our models, our predictive capability will be curtailed,” he said.
While some researchers are suggesting an El Nino may form in 2014, Dr Cai said “it's a bit too early to call”.
Conditions in the Pacific were still in a neutral El Nino phase in the Bureau of Meteorology’s latest report on January 14.
The observing system is backed up by other information sources, such as satellites and the Argo array of more than 3600 free-drifting floats. The buoys, though, provide real-time information over a wide range of the Pacific, detecting changes in moisture, air pressure and near sea-surface temperatures at a fixed point that satellites or Argo floats struggle to match.
The array's performance slide began in 2012 when the US retired one of the ships used to maintain it. Fights in the US Congress over debt ceilings in 2013 then resulted in funding cutbacks that reduced ship visits to the buoys, Dr Legler said.
“We're still seeing the impact of the [cuts],” he said, adding that the US contribution, including ship time, amounts to about $US10 million ($11 million) a year.
Apart from birds or other natural impacts, the buoys are also vandalised or damaged by fishing fleets.
Prior to the cutbacks by both the US and Japan, buoys were typically serviced twice a year, and now some buoys haven't been maintained for a year or more.
Scientists from around the world will gather at the Scripps Institution of Oceanography in San Diego, California next week, to discuss how to sustain or replace the array.
While support may eventually come from countries such as China or South Korea, Dr Legler is optimistic that funding for immediate action will be announced at the meeting.