Stratospheric Impact of the Anomalous 2023 Canadian wildfires: Two Pathways of Smoke

The climate-altering potential of wildfires through their emissions into the stratosphere has only recently been realized following the major wildfire outbreaks in Canada and Australia. The 2023 wildfire season in Canada stood out for its extended burned area and duration, rendering it the most destructive ever recorded. Here we show that the Canadian wildfire season in 2023 was unprecedented in terms of the cumulative fire power, reaching 300 TW h by the end of the season, whereas the PyroCb storms count surpassed by far that of the previous record-breaking events. Using various nadir and limb satellite observations (OMPS-LP, OMPS-NM, MLS, SAGE III as well as geostationary imagers) we explore the nature, the character and the magnitude of the stratospheric perturbation induced by the anomalous 2023 Canadian wildfires.

The data analysis reveals multiple episodes of smoke intrusions into the stratosphere through both pyroconvection (PyroCb) and synoptic-scale process (warm conveyor belt, WCB). Model simulations using MOCAGE chemistry-transport model, constrained by emission data from GFAS (Global Fire Assimilation System) are shown to accurately capture the synoptic-scale WCB-driven uplift of smoke from the lower/middle troposphere to the lowermost stratosphere and reproduce the spatial evolution of the aerosol plumes. The MOCAGE simulation is validated against the multiwavelength LILAS lidar observations in Northern France.

We show that despite the exceptional vigor of the 2023 Canadian wildfires, the depth of their stratospheric impact was surprisingly shallow and limited to the lowermost stratosphere. Conversely, the long succession of moderate-strength PyroCb events, combined with numerous episodes of smoke uplift across the tropopause by WCB process, led to unparalleled levels of pollution at the commercial aircraft cruising altitudes throughout the season.

The research was supported by the French Agence Nationale de la Recherche (ANR) PyroStrat project (Grant No: 21-CE01-0028-01)