In July 2024, a record warming event occurred in the Antarctic stratosphere, disrupting the polar vortex and affecting global weather. This rare event, which is very different from the warming often experienced in the Arctic, could affect weather and ozone levels in the Southern Hemisphere.

Unprecedented warming of the Antarctic stratosphere

Antarctica’s atmosphere was in a restless winter. A series of warming events began in July 2024 in a layer known as the stratosphere, about 30 kilometers above the continent’s icy surface.

In the stratosphere over Antarctica, July temperatures are typically around minus 80 degrees Celsius (minus 112 degrees Fahrenheit). On July 7, the middle stratosphere temperature jumped 15 °C (27 °F), breaking the record for the warmest July temperature ever observed in the stratosphere in the Antarctic region. Temperatures then dropped on July 22, rising to 17 °C (31 °F) on August 5.

These sudden stratospheric warming events surprised atmospheric scientists Lawrence Coy and Paul Newman at NASA’s Goddard Space Flight Center. Coy and Newman develop comprehensive data assimilation and reanalysis models of Earth’s atmosphere for NASA’s Global Modeling and Assimilation Office (GMAO). “The July event was the earliest stratospheric warming observed in the 44-year history of GMAO,” Coy said.

The polar vortex and its impact on wind patterns

The westerly winds in this layer of the atmosphere rotate around the South Pole in the winter, moving at speeds of about 300 kilometers (200 miles) per hour, creating what is known as a polar vortex. But sometimes something happens to disrupt this symmetrical polar flow, causing the wind to weaken and change shape. Instead of passing over the South Pole, the polar vortex lengthens and the wind weakens; the weakening of the winds causes the stratosphere over Antarctica to warm significantly.

The maps above show air temperatures in the middle stratosphere (at a pressure of about 30 kilometers per hour, or 10 hectopascals) on August 5, 2023 (left) and August 5, 2024 (right). The extension of the polar vortex and increasing temperatures near the pole are visible in the 2024 map. Data for the maps come from NASA’s GEOS Advanced Processing (GEOS-FP) model, which assimilates meteorological data from satellites, aircraft, and ground-based observing systems.

The map below shows the potential vorticity (a quantity that describes the rotation of air masses) in the stratosphere on August 5, 2024. Regions of high vorticity potential appear in yellow and have a clockwise circulation; regions of low vorticity potential appear in purple and have a counterclockwise circulation. The polar vortex has lengthened and weakened, and the wind flow has taken on a peanut shape instead of the usual circular pattern.

Comparison of events in the southern and northern hemispheres

Unlike the Arctic, where sudden stratospheric warming occurs about once a year, the polar vortex in the Southern Hemisphere is typically much less active. “In Antarctica, we get sudden warming about once every five years; much less frequently than in the Arctic,” Coy said. That’s probably because the Northern Hemisphere has more terrain that can disrupt wind flow in the troposphere, the layer of air closest to the ground, Coy added. These large-scale tropospheric weather systems move into the stratosphere and disrupt the polar vortex.

July also saw unusual weather conditions in the Antarctic troposphere. Temperatures 4 °C (7.2 °F) above average covered much of the Antarctic continent, and for the Antarctic region as a whole, July 1991 was the fifth warmest July on record. However, Newman noted that it was not certain that weather conditions experienced by humans in the troposphere, including the July blizzard in Australia, could be attributed to sudden warming in the stratosphere.

Impact on weather and ozone concentration

Researchers are also continuing to investigate the origins of surface disturbances that disrupt the stratosphere. “Changes in sea surface temperature and sea ice can disrupt these large-scale weather systems that propagate upward in the troposphere,” Newman said. “But it’s been very difficult to understand why these systems evolve.”

In the stratosphere, scientists have shown that the sudden warming is associated with higher ozone concentrations over Antarctica. The stratospheric ozone layer protects life on Earth by absorbing ultraviolet light, which damages the DNA of plants and animals (including humans) and can cause skin cancer. The change in circulation, combined with the warming of the stratosphere, pulls ozone from other latitudes into the polar region. In 2024, the ozone hole in the southern hemisphere was smaller than normal.