Climate change is disrupting the natural process of recovery for forests and bushland after a fire, potentially leaving carbon dioxide released by fire stranded in the atmosphere and adding to Australia's emissions footprint.
Natural fires have historically been considered "carbon neutral" because, unlike fossil fuel emissions, most of their carbon output is reabsorbed as vegetation recovers.
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| There were more than 100 fires burning in NSW on Thursday, half of them uncontained. Sitthixay Ditthavong |
Pep Canadell, senior principal research scientist at the CSIRO Climate Science Centre, said gross carbon emissions from fires had declined over the past century as firefighting practices and technology improved.
However, worsening drought and more extreme fire conditions could lead to a "breaking point" after which both gross and net carbon emissions from natural fires could increase, Dr Canadell said.
"You can have as many helicopters as you want, but, at some point, it may be that extreme fire conditions become so common ... that you'll be burning more than is regrown".
Fires unrelated to permanent changes to land use had a gross carbon dioxide contribution of 381 million tonnes in 2013, according to the CSIRO's latest available Australian Terrestrial Carbon Budget.
Australia's total greenhouse gas emissions flatlined in the past year at 532 million tonnes of carbon dioxide equivalent.
Bushfires have destroyed 800,000 hectares of national park in NSW this bushfire season, out of a total of 2.1 million hectares burnt across the state.
There were more than 100 fires burning across NSW on Thursday evening, half of them uncontained, as emergency warnings were issued for a 230,000-hectare blaze at Gospers Mountain and a 32,000-hectare fire at Green Wattle Creek near Warragamba Dam.
The NSW Rural Fire Service said it was too late to leave for residents in Colo Heights and Boree, and they were told to seek shelter as the Gospers Mountain fire approached.
The Bureau of Meteorology said Australia had recorded its lowest level of rainfall for the month of November, and that the dry weather would not break for at least three more months.
Dry conditions and strong winds, which averaged 50km/h on Thursday but also produced 80km/h gusts across the ranges, were set to sustain the dangerous fire conditions on Friday.
Meanwhile, the hazardous air pollution in Sydney, the longest and most widespread on record, was expected to linger around the city basin until Saturday.
Dr Canadell said he was unsure whether Australia had hit the "breaking point", but that "unprecedented" disasters - such as the fires that wiped out Tasmania's ancient alpine ecosystems in 2016 - had already occurred.
The 1000-year-old trees destroyed in these fires, including pencil and king billy pines, do not naturally regenerate.
Swinburne University bioscience professor Mark Adams said he estimated bushfires in 2003 and in 2006-07 had released about 550 million tonnes of carbon dioxide.
Scientists declined to speculate on gross emissions from this bushfire season, citing incomplete information about what had been burned and to what extent.
But they noted the vegetation in northern NSW and Queensland was less carbon-dense than the areas in Victoria and Canberra that were worst affected by those earlier fires.
Martin Rice, head of research for the Climate Council, said he was unsure how the emissions footprint of natural fires would change, but that the "root cause" of the escalating bushfire risk was the burning of fossil fuels.
"Climate change is not a thing of the future. It's human-induced, and it's happening now," Dr Rice said.
Australia has committed to reducing its carbon footprint by 26 - 28 per cent by 2030 from 2005 levels, down to 441 million - 453 million tonnes, but observers including the United Nations have questioned its ability to meet the target.
Even if bushfires had a net positive contribution to carbon output, it would not count against the anthropogenic, or human-induced, measures of the national greenhouse accounts.
But Dr Canadell said changing conditions could reopen discussions on methods of carbon accounting.
"We cannot say bushfires are human-induced. But we can say that climate change is human-induced, and that it is having an effect on the fires," he said.
Links
- Australia's use of accounting loophole to meet Paris deal found to have no legal basis
- 'Doing nothing is not a solution': Matt Kean blames climate crisis for bushfires
- Revealed: 'monumental' NSW bushfires have burnt 20% of Blue Mountains world heritage area
- The World Has Reacted To Australia Being Swallowed By Flames
- (AU) 'National Security Issue': Turnbull tells Q&A Morrison Must Step Up Response To Bushfire Crisis
- Leading Scientists Condemn Political Inaction On Climate Change As Australia 'Literally Burns'
- (AU) Dangerous Summer: Escalating Bushfire, Heat And Drought Risk
- (AU) Media Watch: Fire Haze
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