Fires fuelling global warming: study
Carbon emissions from deforestation fires have a significant impact on global warming, according to an international study.
The study, which appears in today's edition of Science, provides the first consensus on the affect of fires on climate change.
"Fire has been underestimated as a contributor to climate change," says study lead author Professor David Bowman of the University of Tasmania.
"In the past it was thought that fires were a steady state."
Bowman says scientists have assumed that the carbon released into the atmosphere from burning plants, was equivalent to the carbon reabsorbed when plants regrow.
But the study's authors note a marked reduction in fire events since 1870, which they speculate may be the result of intense farming and grazing, along with negative attitudes towards fire.
As a result, says Bowman, increased fuel loads and climate change has resulted in more intense deforestation fires. These fires release more carbon into the atmosphere, place increased stress on forest recovery, and result in less carbon being sequestered from the atmosphere.
"If you change the climate then you can see that you're creating a disequilibrium," says Bowman. "The forests are struggling to recover from it."
He says the Black Saturday bushfires in Victoria and recent wildfires in southern California are consistent with the direction of global warming.
The researchers used data from a range of sources including the 2007 Intergovernmental Panel on Climate Change (IPCC) report along with deforestation fire modelling to calculate the impact of fire on climate change during the past 200 years.
They compared the amount of landscape burnt in deforestation fires with the amount of carbon dioxide released from burning.
The researchers found that deforestation fires alone contribute up to 20% of human-caused CO2 emissions since pre-industrial times.
They also found that between 1997 and 2001, biomass burning accounted for about two-thirds of the variability in the CO2 growth rate.
Fire also influences climate by releasing atmospheric aerosols and changing surface albedo (surface brightness), they write.
The study's authors add, "Regionally, smoke plumes inhibit convection, and black carbon warms the troposphere, thereby reducing vertical convection and limiting rain-cloud formation and precipitation."
Dr Jennifer Balch of the National Centre for Ecological Analysis and Synthesis at the University of California Santa Barbara, and co-author of the study, says the models show fire has an impact on greenhouse gas levels, including carbon dioxide, methane and aerosols.
"Fire influences the majority of those terms," says Balch.
According to Balch, a key to managing fire is accepting that it is as an intrinsic part of the planet.
"Fire is as elemental as air or water," she says.
The study's authors say future IPCC assessments of global climate change "should include specific analyses of the role of fire".