Seattle Times | 1 Oct 2021
Amid a record hot summer in large parts of Northern Hemisphere, beset by devastating fires, floods and hurricanes, Antarctica was mired in a deep, deep freeze. That’s typically the case during the southernmost continent’s winter months, but 2021 was different.
The chill was exceptional, even for the coldest location on the planet.
The average temperature at the Amundsen-Scott South Pole Station between April and September, a frigid minus-78 degrees (minus-61 Celsius), was the coldest on record, dating back to 1957. This was 4.5 degrees lower than the most recent 30-year average.
We first learned of this record through a tweet from Stefano Di Battista, who has published research on Antarctic temperatures. The legitimacy of Di Battista’s information was confirmed by Richard Cullather, a research scientist at NASA’s Global Modeling and Assimilation Office.
The temperature averaged over September was also the coldest on record at South Pole, wrote David Bromwich, a polar researcher at Ohio State University, in an email.
The extreme cold over Antarctica helped push sea ice levels surrounding the continent to their fifth-highest level on record in August, according to the National Snow and Ice Data Center.
Extraordinarily cold weather continues to grip the Antarctic Plateau. Maximiliano Herrera, a climatologist who monitors world weather extremes, tweeted that temperature at Russia’s Vostok Station sunk to minus-110.9 degrees (minus-79.4 Celsius) on Thursday (Sept. 30), which was just one degree (0.6 Celsius) from the world’s lowest temperature on record during October.
The current temperatures are still some distance from the coldest ever observed on the continent. In 1983, Vostok plummeted to minus-129 degrees (minus-89.6 Celsius). Satellites have detected temperatures as low as minus-144 degrees (minus-98 Celsius).
Matthew Lazzara, an expert on the meteorology of Antarctica and scientist at the University of Wisconsin, monitored the South Pole temperatures in recent months from his office in Madison with awe. In an interview, he said it was around minus-100 degrees on numerous occasions. Over the years, he’s traveled to Antarctica numerous times to support his research.
“At these temperatures, it is difficult to operate aircraft,” he wrote in an email. “[B]etween -50°C and -58°C you put the aircraft at risk with the hydraulics freezing up or fuel turning into a jelly.”
Once he visited the South Pole in late October. “I got to experience -50°C weather … with a wind chill beyond that. I was *thrilled* to be wearing my 75 lbs of Extreme Cold Weather gear to stay warm,” he joked.
The conditions over Antarctica are in stark contrast to much of the rest of the planet which notched its fourth hottest June through August on record, according to the National Oceanic and Atmospheric Administration. The Northern Hemisphere registered its second hottest summer.
Scientists credited a very strong polar vortex, or a ring of strong winds in the stratosphere, surrounding Antarctica for the intensity of the cold.
The stratospheric polar vortex is a seasonal phenomenon. In the Southern Hemisphere, it forms in the fall, persists through the winter and weakens before reversing course in spring.
The strength of the vortex has connections to weather at the ground, said Krzysztof Wargan, a research scientist with NASA’s Global Modeling and Assimilation Office. He said a strong vortex is associated with low surface temperatures.
Whether the vortex is strong or weak depends on a cycle known as Southern Annular Mode (SAM). Right now, the mode is in its positive phase and the vortex is intense.
“Basically, the winds in the polar stratosphere have been stronger than normal, which is associated with shifting the jet stream toward the pole,” wrote Amy Butler, an atmospheric scientist at NOAA in a message. “This keeps the cold air locked up over much of Antarctica.”
Butler wrote the strong polar vortex not only makes it very cold over Antarctica, but accelerates processes that lead to stratospheric ozone depletion, which in turn can strengthen the vortex even more. This year’s ozone hole over Antarctic is much bigger than average at around 24 million square kilometers, a reflection of the vortex’s strength.
