THE remarkable weather extremes of the past decade, including this year's Queensland and Victorian floods, were not caused by global warming, according to one of Australia's most eminent climate scientists.

Speaking at a major international earth science conference in Melbourne, Professor Neville Nicholls said such extremes as the heat wave in Victoria that accompanied the Black Saturday bushfires, similar heat in Pakistan and Russia, and the devastating tornados that have ripped through parts of the US this year are, in many cases, unprecedented in modern times.

But global warming couldn't be blamed, he said.

"Whenever these things happen people ask 'was it caused by global warming?'," Prof Nicholls told the International Union of Geodesy and Geophysics conference.

"The short answer is no.

"They were all caused by well-known and reasonably well-understood weather and climate events, even with some predictability."

While global warming doesn't cause the weird weather, the professor acknowledges its part in making some of them more severe.

"Global warming doesn't produce these events, however, it's pretty hard to avoid the conclusion that global warming has exacerbated the frequency and the intensity of these heat waves," the Monash University professorial fellow said.

But this year's floods in Australia do not fit into that picture.

"It is much harder to make the connection to link those floods in Queensland in early 2011 to global warming," he said.

"There was a particular and very unusual meteorological sequence that led to those floods and it is very difficult to work out if climate change is exacerbating that situation at all."

The culprit here is a record-breaking version of La Nina, the relative of the drought-causing El Nino.

"This is the largest recorded La Nina event seen in 120 years of recorded history," Prof Nicholls said.

"The only one that comes close was in 1917."

Prof Nicholls' observations draw the inevitable question as to whether global warming has in turn caused the latest version of La Nina to be especially strong.

The answer to that evades him.

"We don't really know," Prof Nicholls said.

Originally published as Crazy weather not climate change - expert