02 Feb 2023
 | 02 Feb 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

How the extreme 2019–2020 Australian wildfires affected global circulation and adjustments

Fabian Senf, Bernd Heinold, Anne Kubin, Jason Müller, Roland Schrödner, and Ina Tegen

Abstract. Wildfires are a significant source of absorbing aerosols in the atmosphere. Especially extreme fires, such as those during the 2019–2020 Australian wildfire season (Black Summer fires), can have considerable large-scale effects. In this context, the climate impact of extreme wildfires not only unfolds because of the emitted carbon dioxide, but also due to smoke aerosol released as high as the stratosphere. The overall aerosol effects depend on a variety of factors, such as the amount emitted, the injection height, and the composition of the burned material, and is therefore subject to considerable uncertainty. In the present study, we address the global impact caused by the exceptionally strong and high-reaching smoke emissions from the Australian wildfires using simulations with a global aerosol-climate model. We show that the absorption of solar radiation by the black carbon contained in the emitted smoke led to a shortwave radiative forcing of more than +5 W m−2 in the southern mid-latitudes of the lower stratosphere. Subsequent adjustment processes in the stratosphere slowed down the diabatically driven meridional circulation, thus redistributing the heating perturbation on a global scale. As a result of these stratospheric adjustments, a positive temperature perturbation developed in both hemispheres leading to additional longwave radiation emitted back to space. According to the model results, this adjustment occurred in the stratosphere within the first two months after the event. At the top of atmosphere (TOA), the net effective radiative forcing (ERF) in the southern hemisphere was initially dominated by the instantaneous positive radiative forcing of about +0.5 W m−2, for which the positive sign resulted mainly from the presence of clouds above the Southern Ocean. The longwave adjustments led to a compensation of the initially net positive TOA ERF, which is seen in the southern hemisphere, the tropics and the northern mid-latitudes. The changes in the lower stratosphere also affected the upper troposphere through a thermodynamic downward coupling mechanism in the model. Subsequently, increased temperatures were also obtained in the upper troposphere, causing a decrease in relative humidity, cirrus amount, and the ice water path. As a result, surface precipitation also decreased, which was accompanied by a weakening of the tropospheric circulation due to the given energetic constraints. In general, it appears that the radiative effects of smoke from single extreme wildfire events can lead to global impacts that affect the interplay of tropospheric and stratospheric cycles in complex ways. This emphasizes that future changes in extreme wildfires need to be included in projections of aerosol radiative forcing.

Fabian Senf et al.

Status: open (until 24 Mar 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review of Senf et al.', Anonymous Referee #1, 08 Mar 2023 reply

Fabian Senf et al.

Data sets

Dataset associated with Senf et al. (2023): "How the extreme 2019-2020 Australian wildfire affected global circulation and adjustments" Fabian Senf, Bernd Heinold, Anne Kubin, Jason Müller, Roland Schrödner, and Ina Tegen

Jupyter Notebooks for Plotting and Analysis of the "Circulation Responses for WiFi-AUS" study, Submission Release Fabian Senf

Fabian Senf et al.


Total article views: 353 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
254 91 8 353 6 2
  • HTML: 254
  • PDF: 91
  • XML: 8
  • Total: 353
  • BibTeX: 6
  • EndNote: 2
Views and downloads (calculated since 02 Feb 2023)
Cumulative views and downloads (calculated since 02 Feb 2023)

Viewed (geographical distribution)

Total article views: 342 (including HTML, PDF, and XML) Thereof 342 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
Latest update: 22 Mar 2023
Short summary
Wildfire smoke is a significant source of airborne atmospheric particles that can absorb sun light. Especially extreme fires, such as those during the 2019–2020 Australian wildfire season (Black Summer fires), can considerably affect our climate system. In the present study, we investigate the various effects of Australian smoke using a global climate model to clarify how the Earth's atmosphere including its circulation systems adjusted to the extraordinary amount of Australian smoke.