THE eastern States might be unseasonably cool, but the deluges devastating Queensland are being helped along by record-smashing warmth in the oceans surrounding Australia.
Warmer oceans promote greater evaporation into the atmosphere, while the prevailing La Nina event is generating the convection currents that act as a conveyor belt to stream that moist air over land.
Australia's oceans are currently the warmest they have been since records began in 1900, according to the Bureau of Meterology (BoM).
BoM climatologist Karl Braganza said October, November and December each "smashed" past records for sea surface temperatures in the region, hovering around 0.6C higher than the long term average.
At a global level, Dr Braganza said, every degree increase in global temperatures translates to about an eight per cent increase in "precipitable water"—water in the atmosphere capable of forming rain.
Of that preciptable water, between 1-4 per cent is actually likely to fall as rain.
Brought down to a local level, the percentages become much harder to predict, but the general principle of warmer sea surface temperatures=greater evaporation=great potential for rainfall, hold true.
The moisture from warm oceans is being brought onshore by convection currents generated by an extremely strong La Niña event.
The December Southern Oscillation Index stood at +27.1, the highest December SOI on record, and the highest positive number since the SOI hit a record in November 1973, just before Brisbane was inundated by the January 1974 floods. The index then peaked at over +30.
Of the seven global computer models used to predict ENSO cycles, two forecast that the current La Niña will persist through to April, and the other five predict either a continuation of La Niña conditions or a relapse back to "neutral" conditions.
Across the globe, the past year saw weather go wild. A heatwave in Russia and eastern Europe, floods in Pakistan and China, and blizzards across Europe and North America were part of a climatically tempestuous year.
Global warming at work?
Dr Braganza noted that one extreme flood event does not a global warming make, but each new climate record adds to the trend that points to the underlying effect of warming.
While the computer models can't yet predict how global warming will play out in through the El Niño/La Niña-Southern Oscillation (ENSO) cycles, they have repeatedly predicted that warming will lead to increased "hydrological intensity", or greater extremes of drought and flood, along with temperature extremes.
US agencies NASA and NOAA this week reported that 2010 tied with 2005 as the warmest year on the instrumental record, which began in 1880, and was also the wettest year recorded for the planet. The past decade has also been the warmest on record. Twelve of the warmest years recorded have occurred since 1997.
In November, the World Meterological Organisation reported that greenhouse gas levels had reached their highest levels since pre-industrial times.
The warming effect, or "radiative forcing" of increased greenhouse gases grew by 27.5 per cent between 1990 and 2009, the WMO said.
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