Record-breaking aerosol levels explained by smoke injection into the stratosphere

Area of Science:

• Atmospheric Science
• Climate Science
• Environmental Science

Background:

• Early 2020 witnessed unprecedented aerosol optical depth (AOD) levels across the Southern Hemisphere (SH).
• Monthly AOD values in most SH regions surpassed average levels by over three standard deviations, excluding tropical areas.

Purpose of the Study:

• To investigate the causes behind the anomalous AOD in the SH during early 2020.
• To quantify the impact of stratospheric smoke injection on regional climate.

Main Methods:

• Analysis of aerosol optical depth (AOD) data.
• Attribution of AOD anomalies to specific meteorological and geographical factors.
• Estimation of stratospheric smoke mass and its radiative forcing.

Main Results:

• The Australian bushfires of 2020 were identified as the primary cause of the record AOD.
• Deep convection associated with mid-latitude cyclones transported smoke to the stratosphere.
• Stratospheric smoke mass reached approximately 2.1 ± 1 teragrams in January 2020.
• A cooling effect of over 1.0 ± 0.6 W/m² was observed over cloud-free oceanic areas.

Conclusions:

• The location and intensity of the Australian bushfires led to significant stratospheric smoke injection.
• This stratospheric smoke had a measurable cooling effect on the climate system over oceanic regions.