Australia is already experiencing an increase in extreme conditions from climate change and more sophisticated modelling is allowing scientists to pinpoint humans' contribution to the wilder weather, the Bureau of Meteorology and CSIRO said.
The fourth State of the Climate report found Australia's mean surface temperature has risen by about 1 degree since 1910, rainfall patterns are shifting away from the nation's south, and there is a marked increase in heatwaves and extreme fire weather days.
"Climate change is happening now and it's having a tangible impact on Australia," Karl Braganza, manager of the bureau's climate monitoring, said.
The fire season is now extending "by a matter of weeks on average", as warmer conditions arrive sooner and last longer over much of the country, he said.
In the future, as rising greenhouse gas levels drive increases in surface temperatures, the frequency of hot days including those bearing extreme fire weather will rise further, Dr Braganza said.
The biennial report adds to the growing body of evidence Australia's climate is changing, and comes days after CSIRO told Fairfax Media that levels of carbon dioxide – the most potent greenhouse gas – are rising at a record annual rate.
While surface temperatures fluctuate sharply – driven by the El Nino-La Nina cycle – the report focuses on the increasing proof that the oceans are heating up.
"The oceans really provide us with the most reliable indicator of how the globe as a whole is warming," said Steve Rintoul, interim director of the Climate Science Centre at the CSIRO.
Oceans have taken up taken up more than 90 per cent of the extra heat trapped by the rising levels of greenhouse gases since 1960. .
Even so, the trend for surface temperatures is also clear.
The chances of very warm monthly maximum temperatures have risen more than five-fold for the 2001-15 period compared with the baseline 1951-80 period, with a similar rise in abnormal minimum temperatures. See chart below.)
"In the last one-two decades, as that distribution shifts further to the right ... you have a noticeable increase in extremes," Dr Braganza said.
The changes of extreme heat events – often accompanied by worsening fire weather – have also increased markedly in recent decades.
For instance, 2013 – the nation's hottest year on record – had 28 days that were in the top 1 per cent for mean temperatures for their respective month. The bureau counted that many extreme heat days over the entire first 31 years of its existence. (See chart below).
An innovation from previous reports is the evidence that humans' contribution to extreme weather can now be quantified.
Researchers used climate and weather models to examine the extremely warm October-November 2014 period, when daytime temperature anomalies were almost 2.5 degrees above average. Using 1960-like levels of greenhouse gases, Australia would have been warm but not record breaking. .
"We know that climate change changes the odds of these extreme events, and what is new is the ability quantify the contribution to a particular event from human-driven climate change," Dr Rintoul said.
A similar study of September 2013, another record breaker, found global warming's contributed 15 per cent.
Recent research has added to the understanding of other trends, such as the drying out of southern Australia during the growing season.
South-west Western Australia, for instance, has seen its May-July rainfall drop almost 20 per cent since 1970, as storm tracks shift southwards, taking the rain with them.
For south-eastern Australia, the drop is less pronounced – at 11 per cent over the April-October period – but still leading to a sharp slide in stream flows.
"Areas of southern Australia will probably spend more time in drought [in the future]", Dr Braganza said. "But when the rain does fall, it's likely to be heavier than it was in the past."
Tropical cyclones are reducing in frequency – a trend that is likely to continue – although their intensity is expected to rise later this century.
While wind speed is one issue, rising sea levels and heavier deluges mean the impact of the tropical tempests is likely to worsen even if they don't strengthen, Dr Braganza said.
This story was first published on The Sydney Morning Herald.
The story Australia experiencing more extreme fire weather, hotter days as climate changes first appeared on Farm Online.