THE floods inundating northern NSW and Queensland are likely to have been driven in part by human-induced climate change - although the precise extent of this influence won't be known for another decade.
Leading climate researchers said the frequency of El Nino and La Nina events that bring drought and flood to Australia seems to have increased in the past 30 years, even though such events have been occurring independently of human influence for far longer.
''It's completely naive to exclude climate change as a contributor to the floods because of the rapid warming of the oceans, but we are not yet at the stage where we can be too specific about individual events,'' a climate researcher at the University of NSW, Matthew England, said.
The El Nino/La Nina-Southern Oscillation, or ENSO, is a cycle caused by warm sea-surface temperatures and air-pressure changes, and is a principal driver of weather in the southern hemisphere.
Unusually, Australia has endured two La Ninas in the past 18 months, leading to the nation recording the wettest two-year period since instrumental records began in the 1880s.
''Some of the main El Nino and La Nina reconstructions available show a significant trend in the cycles over the past century and particularly in the last 30 years,'' Professor England said. ''We are getting more El Nino and La Nina events.
''One thing that's certain is that the water north of Australia has warmed about 0.7 degrees above the long-term average. For this key region, we are in the situation now where the long-term trend is as significant as natural variability.''
Recent studies overseas have drawn similar conclusions. A paper published this week in the journal Nature Climate Change reported an increased frequency of ENSO in the past 30 years.
''This means we should anticipate more extreme events, such as flooding,'' the paper's lead author, the University of Auckland scientist Anthony Fowler, said.
Australia's Bureau of Meteorology said current weather patterns were proceeding as predicted in the first report of the Intergovernmental Panel on Climate Change in 1990.
''Since about 1990, all the climate models have been producing the same or similar results, and that's what we are seeing now,'' a bureau climatologist, Karl Braganza, said. ''There is more heavy rain in the tropics, as well as more drought in southern Australia.''
But the complexity of local and regional weather patterns means drawing a causal link between the weather of the past two years and climate change - and therefore between the floods and the greenhouse gas emissions from human activity - is difficult.
''We are probably another decade away from clearly identifying the signals from today,'' Dr Braganza said.