Australian wildfires drove record breaking aerosol levels over Southern Hemisphere

According to a new study, Australian brushfires injected vast amounts of smoke into the stratosphere resulting in 2020's record breaking levels of atmospheric aerosols over the Southern Hemisphere. According to the findings, the aerosol's atmospheric impact was comparable to that of a moderate volcanic eruption and caused marked cooling over cloud free ocean regions.

While the lifetime of aerosols in the lower atmosphere can range anywhere from minutes to weeks, those that reach the stratosphere can persist for months or even years and have a considerable impact on Earth's radiative budget. This effect is most strikingly observed following explosive volcanic eruptions, which blast aerosols high into the upper atmosphere. Currently, biomass burning is generally considered to be one of the leading sources of atmospheric aerosols.

During the early months of 2020, record breaking levels of aerosol optical depth (AOD) - a common metric used to estimate aerosol load in the atmosphere and calculate its radiative effects were observed over the Southern Hemisphere, exceeding monthly averages for much of the region by more than three standard deviations.

The 2020 levels even eclipsed those measured after the eruption of Mount Pinatubo, the second-largest eruption of the 20th century. Eitan Hirsch and Ilan Koren attribute this AOD anomaly to the particularly intense and widespread fires in southeast Australia during the 2019 to 2020 Australian wildfire season.

Using a combination of data from two satellite missions, Hirsch and Koren developed a time series of AOD measurements from 1981 to 2020 and evaluated the fate and effects of Australian wildfire smoke. According to the findings, the record breaking levels of wildfire smoke in the stratosphere were made possible through a combination of the intensity of the fires, and due to their location at a latitude with a shallow tropopause and within the mid-latitude cyclone belt, where energetic convection lifted smoke into the stratosphere and spread it uniformly around the hemisphere.

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