Australia may face more intense and frequent bouts of extreme weather in the future as global warming "energises" the El Nino-Southern Oscillation (ENSO), the dominant climate system over the Pacific, according to an Australian-led team of researchers.
The research, led by Shayne McGregor at the University of NSW's Climate Change Research Centre, found that the ENSO phenomena were more active and intense during the 1979-2009 period that at any time in the past 600 years.
"Our research suggests in a warming world we are likely to see more extreme El Nino and La Nina events, which over the past decade in Australia have been related to extreme flooding, persistent droughts and dangerous fire seasons," said Dr McGregor.
An El Nino occurs when the central and eastern Pacific waters are relatively warm, weakening easterly trade winds. A reduction in clouds typically results in droughts and heatwaves for eastern Australia in particular, such as during 1982-83 and 1997-98.
La Nina years see the patterns reverse, with sea-surface temperatures to Australia's north relatively warm, with floods more common.
"In Australia we don't want El Nino to become more variable," said Matthew England, a co-author of the report published in the Climate of the Past journal, and also from the Climate Change Research Centre. "We're possibly having slightly more events, and they're becoming more intense when they do occur."
The opposite looks likely to be true, however, as humans pump more greenhouse gases into the atmosphere, driving temperatures higher.
"If we warm the planet we tend to energise El Nino," Professor England said. "We tend to excite it to become more variable, and so the events become stronger."
Karl Braganza, manager of climate monitoring at the Bureau of Meteorology, said research is ongoing to examine the link between climate change and extreme weather.
"If they can show a relationship with global temperatures [and ENSO variance], that's a pretty important result," Dr Braganza said of the latest research. (A separate study out earlier this month found that ENSO systems could have a greater impact on Australia in the future even if they did not intensify.)
Australia's extraordinary run of above-average temperatures continued in October despite ENSO being a "neutral" mode, neither El Nino or La Nina.
Sydney, for instance, recorded its second-hottest October on record by daytime and equalled the highest number of days of 32 degrees or warmer weather at five. Brisbane had its hottest October with an average maximum of 28.8 degrees.
Nationally, this month will probably be among the 10 warmest Octobers over the past century, the bureau said. That's enough to make both the past 12 months and the year-to-date periods, the hottest on record for Australia.
"A lot of climate experts are expecting the global climate to take a step up the next time an El Nino occurs," Professor England said. "Temperatures that year will break records in a significant way."