Scientists ‘careful’ in attributing fire weather signals

Scientists are reluctant to claim a definitive climate change signal in bushfires ravaging eastern Australia because of the complex factors involved.

Sarah Perkins-Kirkpatrick, a future fellow at UNSW’s Climate Change Research Centre.

Scientists are reluctant to claim a definitive climate change signal in bushfires ravaging eastern Aust­ralia because of the complex factor­s involved.

Sarah Perkins-Kirkpatrick of the University of NSW said the detection of a climate change ­signal in bushfires was still a work in progress.

“With temperature we can ­absolutely detect a human signature behind it, but it gets more complex to get this climate signal when we include more variables,” Dr Perkins-Kirkpatrick said.

Climate models weren’t always as good for humidity and wind speed as they were for temper­ature. “We have to be careful how we attribute fire weather. We can’t say one specific fire or all the ingredients that go into fire weather are due to climate change, but we can certainly tear out that climate change has this signal in some of those ­ingredients.”

Weather patterns in the Indian Ocean will probably be a contributing factor for this fire season. Despite weakening over the past fortnight, the Indian Ocean ­Dipole remains strongly positive.

The latest update from the ­Bureau of Meteorology says the IOD is so strong that it is likely to be slow to decline and could persist­ into midsummer.

“Typically, a positive IOD brings below average spring rainfall to southern and central Australia, with warmer days for the southern two-thirds of the country,” the BoM said. “Positive IOD events are often associated with a more severe fire season for southeast Australia.”

A briefing organised by the Australian Science Media Centre on Wednesday explored the signific­ance of ongoing fires, whether climate change was responsib­le and what action was needed for the future.

Ross Bradstock of the University of Wollongong said the fires raging in NSW were now in ­uncharted territory. The fires exceed­ past bushfire seasons, including December 2001 and January 1994, and were approaching other significant fire seasons such as in Victoria in 2003 and 2006.

Professor Bradstock said all the fires were located in diverse forest environments where fuel was more or less present most of the time. The areas were experiencing extreme dryness because of prolonge­d drought and the fires were exacerbated by hot, dry, windy weather.

“All the ingredients are there for rapid development of major fires and it is no coincidence when you examine the Bureau of Meteorology’s long-term rainfall deficits and temperature averages,” Professor Bradstock said.

The World Meteorological ­Organisation said the bushfires in Australia were due to a combination of factors including low soil moisture, heat and, importantly, wind direction and speed.

WMO spokeswoman Clare Nullis said the most extreme 10 per cent of fire weather days had increased in recent decades across many regions.

“There has been an associated increase in the length of the fire weather season and climate change, including increasing temperatures, is contributing to these changes,” Ms Nullis said.

A report by the Climate Council said the “catastrophic, unprecedented fire conditions currently affecting NSW and Queensland have been aggravated by climate change … Bushfire risk was exacer­bated by record-breaking drought, very dry fuels and soils, and record breaking heat.”

The Climate Council said bushfire conditions were now more dangerous than in the past.

“The fire season has lengthened so substantially that it has ­already reduced opportunities for fuel reduction burning,” it said.

“This means it is harder to prepare for worsening conditions.”

David Bowman of the University of Tasmania said it was very possible to manage fuels and creat­e fire safe environments but that was an enormous research and practical challenge given the changing climate.