A Rare Heat Spike Above Antarctica Could Mean More Extreme Weather via a Destabilized Southern Polar Vortex

A rare temperature spike in the atmosphere high above Antarctica is threatening to split the southern polar vortex, bringing with it the potential for extreme weather events across the Southern Hemisphere.

In July 2024, a Sudden Stratospheric Warming (SSW) event was detected in the skies above the Southern Ocean that surrounds Antarctica, with temperatures spiking over 60°C (140°F) above normal at an altitude of roughly 30 to 40 kilometers (18.6 to 24.9 miles). While this phenomenon happens every few years in the Northern Hemisphere, it is extremely rare in the south, with the only other known SSW above Antarctica occurring in 2002.

This warming event has already caused the southern jet stream—the high-speed air current that marks the boundary between the polar vortex and the mid latitudes—to slow substantially, dropping from its usual 300 km/h (186 mph) to 230 km/h (143 mph), a decrease of nearly 25 percent.

Along with this sudden warming event, this slowing of the jet stream is threatening to destabilize the southern polar vortex, an event that might result in more extreme weather for regions in the Southern Hemisphere: typically, both polar vortices are fairly orderly wind patterns that circle each of the poles, held in place by the contrast of warm air in the mid latitudes and colder air closer to the poles.

However, as more heat is trapped near the planet’s surface the excess energy finds its way toward the polar regions, resulting in the disproportionate heating of the Arctic and Antarctic regions that are being seen today.

That disproportionate warming between the polar regions and mid latitudes causes the ordinarily stable polar vortices to meander off course, causing lobes of relatively cool polar air to extend away from the poles. This effect was behind the devastating plunge in temperatures in the U.S. south in February 2021; with the Southern Hemisphere currently in austral winter, similar effects could be experienced in Australia, New Zealand, South America and perhaps even southern Africa.

Forecasts for the destabilization of the southern jet stream are split between an upcoming stabilization of the current, and a more dramatic collapse of the pattern; if the later occurs, the destabilized jet stream is expected to disrupt a weather pattern called the southern annular mode (SAM), a major factor affecting Australia’s climate, possibly sending the system into a negative phase that would result in exceptionally dry and hot conditions for both Australia and South America over the upcoming summer season.