Living in Tasmania stories
SAM fires up our hottest summer
Tasmania has just experienced its hottest summer ever recorded, with temperatures 1.8 degrees higher than average.
Seawater around our coasts was up to 3 degrees warmer than average and was linked to a crippling outbreak of Pacific Oyster Mortality Syndrome and a production challenge for salmon farmers in Macquarie Harbour.
Low rainfall and ferocious dry lightning strikes sparked bushfires that raged for a month and a half, while Hydro Tasmania’s dam storages have dived to an unprecedented 13.6 per cent.
While some simply rail against the Tassie weather, others are sure we're experiencing human-induced climate change.
As scientists work on answers, a phenomenon called SAM (the Southern Annular Mode) has emerged as a part-explanation for what is happening – if not for why.
Dr Michael-Shawn Fletcher and PhD student Michaela Mariani of the University of Melbourne have found that a southerly shift in prevailing westerly winds is disturbing weather patterns previously regarded as normal.
Dr Fletcher, who has built a career studying long-term interactions between humans, climate and vegetation, said: “My conviction is that the current trend is evidence of anthropogenic forces.”
During a negative SAM westerlies shift northward, but during a positive SAM, like the 2016 version, the winds move south. Tasmania then misses out on the moisture the winds carry and drier conditions prevail.
As the cold fronts that make our weather so changeable slip away to the south, the consequences can be grim.
The Melbourne study included an analysis of charcoal deposits from western Tasmanian fires over the past 1,000 years, including some that had occurred on the same ground as the 2016 fires.
The rise and fall in the amount of charcoal deposited since around 1,500AD closely matches a SAM index compiled by scientists.
There has been a particularly steep rise in charcoal in recent times.
“Correlation isn't causation,” Dr Fletcher said. “But it’s a well-described phenomenon that ozone depletion has caused a positive trend in SAM and we’ve got clear evidence that the SAM index in the 21st century has exceeded anything that’s occurred in the past 1,000 years.”
The researchers also found a close match between actual records of SAM and observed fire activity over the past 30 years.
“If you have a dry autumn, winter, spring you’ve got more fires in summer,” Dr Fletcher said.
The research, published in Geophysical Research Letters by the American Geophysical Union, concluded that "there had been a spike in fire activity in the 21st century in response to natural and anthropogenic SAM trends".
Dr Fletcher said while the impact of the Pacific Ocean’s El Niño (a seasonal warming of the sea surface) on fire frequency in Tasmania had been recognised, relatively little attention had been paid to the impact of SAM.
“We've ignored the fact that in Tasmania, at least, fires are also modulated by this other system,” he said.
“What we have here in this current year is the fifth-strongest El Niño event recorded and the second most positive SAM event on record. It’s a double whammy.”
UTAS’s senior fire ecologist, Professor David Bowman, said the Melbourne research opened up a possibility of using SAM to provide early warnings of severe fire conditions.
In a report in Environmental Research Letters, Professor Bowman, argues that Australia’s highly varied climate makes it difficult to predict fire activity.
Professor Bowman said: “You can’t predict precisely, but you can use climate modes like SAM to help you forecast bad fire seasons.
“It’s just a guide, but it’s important.”
Professor Bowman said: “Large-scale fire events in Tasmania in the past have been very rare and we're beginning to see them more frequently. There’s evidence we're seeing anthropogenic climate change.”
He described this summer’s fires in usually moist western regions as "an historically significant event".
Among those who strongly agree, is The Guardian’s Karl Mathiesen who went so far as to compare the Tasmania’s fires with the destruction of ancient Palmyra by ISIS.
He wrote: “On 13 January a huge, dry electrical storm set more than 70 fires rampaging across the island. Within days the flames tore through the dried-out defences and into the world heritage area above.
“For more than a month, fire has rolled back and forth across the fragile plains.
“The beginning of its end is a theft from us all. Two-thirds of the plant species on the plateau exist nowhere else on earth but Tasmania.
“According to one estimate, 4 per cent of the world’s remaining pencil pines – among the longest living of all trees – have been lost in these blazes.”
Mathiesen included in his report the important fact that damage has been limited to 22,000ha (about 1.4 per cent) of the vast World Heritage Area.
But he left his readers to ponder the identity of the "ISIS" that had unleashed its vandalistic fires on a slice of Tasmania’s Palmyra.
Some less-circumspect critics of the stretched and heroic State Fire Service and Federal and State leaders talked about the "previously fire-free" World Heritage Area.
This ignored the scientific records used by Dr Fletcher and also disregarded what we know of Aboriginal land management in Tasmania over the past 30,000 years.
The role of Aborigines in managing landscapes with fire – using regular small-scale burns to avert mega-fires – is important in understanding our fire history and could offer a way to manage our fire future.
Author Bill Gammage suggests in his intricately researched book, The Biggest Estate on Earth, that Aborigines used skilfully controlled and frequent fires over long periods of time to shape the landscape from Cape York to Tasmania.
European settlers were generally unaware that the park-like gazing land they took over in eastern Australia was not a natural landscape, but a gigantic game park carefully constructed and maintained by thousands of generations of people with fire sticks.
The fine detail of how the Aborigines burnt different types of natural vegetation in Tasmania to encourage marsupials and to preserve plant diversity was lost forever in the post-settlement holocaust.
Modern Tasmanians, including Aborigines, need to do some re-learning in a vulnerable eco-system that is now at risk of having the moisture squeezed out of it again and again by further coincidences of SAM and El Niño.
In a recent article in Wild magazine, Melbourne-based writer and conservationist, Nick Rodway, wrote: “The conversation as to the implementation of fire stick farming will no doubt continue for some time.
“Fire stick farming has an ancient history and is not something that should be dismissed lightly, and nor should the influence of Aboriginal Australia on the landscape.
“Their lessons serve us well if we choose to embrace them.”
4 April 2016, Tasmania’s Stories Edition 170