Victoria’s bush fire smoke reached stratospheric heights

Posted on September 5, 2011

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Landmark study probes impact on global climate science:

Smoke from Victoria’s disastrous bushfires of 2009 circled the globe for more than three months, at heights previously thought unlikely, a La Trobe University study has found.

The findings have been published in the leading Journal of Geophysical Research

They challenged conventional scientific wisdom that fire-borne aerosols – unlike those found in volcanic smoke – do not pollute the stratosphere (the atmosphere above 16 km) to any great extent.

The study was carried out by PhD researcher Jason Siddaway and lecturer in physics, Dr Svetlana Petelina.  The La Trobe research findings are significant as airborne particles released by bushfires –  such as soot and other aerosols, known to scatter and absorb solar radiation – are typically thought to remain in the lower atmosphere close to their source.

‘Climate models pay little attention to the scattering and absorbing effects of fire-borne aerosols in the stratosphere because in the past they did not seem to reach altitudes above 16 km in such high quantities. At these altitudes, circulation patterns can quickly distribute a plume of pollution around the globe, possibly leading to global cooling effects,’ the researchers said.

Extreme fires and climate modelling

Volcanic eruptions have long been considered the usual pathway by which climate-affecting aerosols and chemicals are injected into the stratosphere from the Earth’s surface. However, the 2009 Victorian bushfires showed otherwise. The researchers found that the lifespan of fire-borne particles from those fires in the stratosphere was similar to that from a volcanic eruption.

 ‘This suggests that extreme fires could have a global effect and should be considered in climate models,’ they say. ‘Studying transport of smoke particles from this and other fires may help trace stratospheric circulation patterns, which are not yet completely understood,’ they added.

The La Trobe researchers worked with data from the Optical Spectrograph and Infrared Imager System on the Odin satellite. They established that the dense smoke cloud from the bushfires penetrated the stratosphere on 11 February 2009.

‘The plume travelled westward, circling the globe in about six weeks, steadily reaching higher altitudes,’ the researchers say. ‘The amount of particles in the stratosphere from the fire decreased by half every 19 days from mid-February to the end of April 2009.  By mid-June 2009 the plume had dispersed.’

See the full report of the study here