気候変動：30年間の記録上最大の成層圏昇温とオーストラリアの森林火災の関連性

The South-Eastern Australian bushfires between 2019 to 2020 released smoke particles into the Earth’s upper atmosphere that contributed to the highest recorded temperature in the lower stratosphere since the early 1990s, reports a study published in Scientific Reports.

The Australian bushfires caused millions of tons of smoke aerosols to be released into the Earth’s atmosphere. Unusually, a significant amount of the smoke reached elevations as high as the lower stratosphere which starts at altitudes of around 15 kilometers over Australia. Abnormally high temperatures (the highest since 1992-1993) were also observed in the lower stratosphere for several months around this time.

Lilly Damany Pearce and colleagues investigated whether the smoke aerosols emitted from the Australian bushfires led to these increased stratospheric temperatures. The authors used data from the CALIPSO and Suomi National Polar-orbiting Partnership satellites to monitor aerosol levels in the stratosphere in the southern hemisphere between December 2019 and 2020. As a comparison, they also investigated aerosol levels recorded by the same satellites between June 2012 and December 2018. The authors report an initial plume of smoke that reached altitudes of 16 kilometres on 31 December 2019 and detect a similar plume on 12 January 2020. The smoke aerosols eventually reached altitudes of between 25 to 35 kilometres and were detected throughout 2020.

The authors applied these findings to the United Kingdom Earth System Model version 1 (UKESM1) climate model in order to estimate the impact of these plumes on lower stratospheric temperatures. The authors modelled the effects of smoke aerosol, changes to the ozone layer, or a combination of both factors on stratospheric temperatures, and compared these to control simulations of present-day climate. In the smoke aerosol and ozone simulation, the authors modelled significantly increased temperatures compared to the present-day climate in the lower stratosphere throughout January to June 2020. There was a modelled temperature increase of around 0.65 degrees Celsius from November 2019 to March 2020, which is similar to the observed temperature spike of 0.7 degrees Celsius during this period. This suggests that the increased stratospheric temperatures in the model were due to bushfire smoke aerosols, according to the authors. They suggest that the modelled temperature spike is the largest since the eruption of the volcano Pinatubo in 1991 that released sulfate smoke aerosols into the stratosphere.

The authors conclude that, as it is predicted that climate change will increase the frequency and intensity of future wildfires, this may in turn increase the probability of more events of stratospheric warming and ozone depletion from smoke aerosols.