An extraordinary weather event is currently happening over the Antarctic continent. It is marked by a surprising rise in stratospheric temperatures. Air temperatures in this layer, located about 12 to 40 kilometers above the ground, have recently increased by up to 35°C above their usual levels. Normally, the strong stratospheric polar vortex and the lack of sunlight during the polar winter would keep temperatures around -55°C at certain heights, yet recent observations show a sharp rise to about -20°C.
This sudden warming began in early September and is still ongoing, to be precise. It seems to be a result of a “sudden stratospheric warming” (SSW) event. This phenomenon describes the unexpected warming of the stratosphere, which is usually extremely cold during the Antarctic winter, averaging around -80°C in its deeper parts and warming to only -50°C by late September. The current warming has occurred in at least three separate pulses, each resulting in temperature increases of 25°C or more, showing a pattern of spikes and retreats. Large-scale atmospheric waves are the source of this heat. These waves have traveled from the Earth’s surface into the Antarctic stratosphere, transferring heat as they interact with the strong winds of the stratospheric polar vortex. This upward energy transfer can happen only during the Antarctic winter when the polar winds are at their strongest.
The stratospheric polar vortex is a large area of rotating winds high above both the Arctic and Antarctic. SSW events significantly impact it. In the Southern Hemisphere, these disturbances usually happen at an altitude of about 30 kilometers, just north of the Antarctic coast. The term “sudden” here means a timescale of days or weeks, not an instant change, and it is also used because these events are unexpected and extremely difficult to predict.
While SSW events are fairly common in the Northern Hemisphere, occurring roughly every two years, the intense stratospheric winds over Antarctica, which can reach speeds of up to 300 km/h, have made large-scale warming very rare in the south. The narrow definition of an SSW, which requires the complete disappearance of the polar vortex, has only been met once in the Southern Hemisphere records—during the extreme event in 2002. Research suggests that using a broader definition, which includes a significant weakening of the polar vortex and the related sudden warming, shows that these events, including those like the ones in 2019 and 2024, are likely more frequent—estimated to occur once every 22 years instead of once every 60 years under the narrow definition. Efforts are currently underway to improve detection methods for these phenomena in the Southern Hemisphere.
The effects of Antarctic stratospheric warming go beyond the pole. These events can greatly influence global weather patterns. A typical result for southeastern Australia after an Antarctic SSW is a drier and warmer spring and summer, a pattern seen in 2019 that contributed to the severe megafires of the 2019–2020 “Black Summer.” In contrast, a frigid polar stratosphere is linked to cooler and wetter conditions, as observed during the 2023–2024 period. Additionally, a warmer stratosphere means less ozone depletion and increased ozone transport from the equator, which helps block harmful ultraviolet radiation, but these ozone changes can also lead to unexpected weather systems.
This prediction is due to the continued warm ocean temperatures that drive more evaporation and rainfall, adding complexity to the stratospheric influence. As weather systems are chaotic and shaped by many interacting factors, the complete impact of the current stratospheric warming is still uncertain. To track any potential effects on surface weather, it is crucial to continuously monitor seasonal forecasts throughout the summer.
