ACHIEVING the Holy Grail of climate forecasting, an accurate, reliable guide to the season ahead when farmers are making their management decisions is difficult enough.
Climatologists have to deal with complex interactions between a range of climate drivers such as the El Nino / Southern Oscillation (ENSO) in the Pacific Ocean and the Indian Ocean Dipole (IOD) in the Indian Ocean and a host of other factors before coming up with a prediction.
And now research is showing their job is likely to be even harder in the future.
CSIRO was part of a team that issued a report this week that has found global warming will make it more difficult to predict multi-year global climate variations, a consequence of changes to long-term climate variability patterns in the Pacific Ocean.
The results, published in Nature Climate Change, shed light on how the Pacific Decadal Oscillation (PDO) was responding to a changing climate, with implications for assessing multi-year risks to agriculture.
The PDO is a long-term pattern of Pacific climate variability, operating in the Pacific Ocean, and exerting a substantial influence on climatic conditions around the Pacific Rim.
The PDO has two phases, cold and warm, with the cold phase associated with higher than average rainfall in Australia and the opposite in a warm phase.
The PDO also influences how heavily climate drivers such as El Nino, which causes warm and dry conditions in north, west and east of Australia will impact weather for that particular season.
"When we're in a Pacific Decadal Oscillation cold phase, El Nino is more likely to affect Australian rainfall and surface temperatures," researcher Dr Wenju Cai from CSIRO's Centre for Southern Hemisphere Oceans Research (CSHOR) said.
"With a less predictable PDO, it may be more difficult to predict the likely impact of El Nino," Dr Cai said.
The research found that the PDO would become less predictable as the planet warms, because warming conditions result in a significantly shortened PDO lifespan.
Using various greenhouse gas emissions scenarios, researchers found that the predictability of the PDO sharply declined depending on the intensity of warming.
The results pose a challenge for predicting regional climates on multi-year timescales, as well as year-on-year climate variability.
"In our current climate, we can potentially predict the PDO approximately eight years ahead. That lead time will likely be reduced to three years by the end of the 21st century," Dr Cai said.
The ability to accurately forecast the PDO helps decision-makers understand and plan for warm and cold oceanic conditions.
CSIRO is currently developing skilled forecasting models to help guide decision makers manage risk under a warming climate.
Dr Cai said these macro-climatic factors had important implications on day-to-day weather.
"Many people are familiar with the role that the El Nino-Southern Oscillation plays in climate but might be surprised that there are bigger forces at play like the PDO, which influences our marine environment, as well as climate extremes."
CSHOR is a $20 million five-year collaboration between CSIRO, Qingdao National Laboratory for Marine Science and Technology with the University of Tasmania and University of New South Wales.