BAMOS November 2025
6 Article
Another Sudden Stratospheric Warming in 2025: what’ s happening to the atmosphere?
Dr Martin Jucker, University of New South Wales( martin. jucker @ unsw. edu. au)
Visualisation of the sudden stratospheric warming over the pole on 5 September 2025. The blue area shows the cold air mass inside the polar vortex which gets pushed off the pole by anomalously warm air over the Southern Ocean( red). Credit: Martin Jucker
“ A Sudden Stratospheric Warming! A Sudden Stratospheric Warming!” Like any reasonable person, this kind of alarm would get me out of bed in seconds.
You see, I’ ve been part of a study that suggested we would never see one of these events again in the Southern Hemisphere because of climate change.
Yet, it’ s September 2025, and a sudden stratospheric warming is happening— only about a year after the last one in July-August 2024. So, what’ s going on?
I’ ll share my guess in this article, but first, let’ s start with some basics.
What is Sudden Stratospheric Warming?
Sudden Stratospheric Warming( SSW) is a relatively rapid and strong warming of the upper atmosphere( around 30 km) above either pole during winter.
If it’ s strong enough, it can completely disrupt the polar vortex— a mass of very cold air over the pole surrounded by strong westerly winds.
One immediate effect of SSW in the Southern Hemisphere is the inhibition of destructive ozone chemistry, which is why we typically see a weaker or smaller ozone hole during these events( Figure 1).
A somewhat slower effect is the influence on the Southern Annular Mode( SAM), which tends to become temporarily negative during an SSW. This, in turn, brings a hotter and drier spring / summer to southeastern Australia.
How frequent are SSWs?
SSWs occur on average once every two years in the Northern Hemisphere. To be classified as SSWs, warming events need to disrupt the polar vortex.