Weakened polar vortex seen as likely culprit behind China's big chill

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BEIJING — The cause of a wave of bitingly cold air that swept into China and rewrote seasonal records for low temperatures may lie further north — a potential weakening in the wall of fast-moving air currents that normally hold back blasts from the Arctic.

With winds that triggered the highest warnings for gales from Chinese authorities, a powerful cold wave entered China via Xinjiang on Dec 13. It quickly headed east, encasing the Chinese capital Beijing in icy weather, and within a few days, crossed the Yangtze and brought rare snowfall to hilly regions as far south as Guangdong.

Cold winters are common in China. But the significantly lower temperatures and the longer duration of the current cold wave suggests a possible leak in the circular band of cold air moving around the Arctic, known as the polar vortex, which normally wraps closely around the North Pole and keeps the Arctic air from invading lower latitudes.

In recent years, meteorologists have blamed the buckling of the polar vortex, which moves at bullet-train speeds from west to east at altitudes of up to 50 km, for the bitter cold that periodically descends on North America.

"Over the past 30 years, the Arctic Circle has experienced the fastest warming globally, known as the 'Arctic amplification' phenomenon," said Shao Sun, a climatologist at the University of California, Irvine.

"Warming leads to a weakening of the polar vortex in the Arctic, making it easier for cold air within the vortex to move southward, contributing to the occurrence of cold wave events."

Debate remains over whether such weakening in the polar vortex has become more common and the direct role played by global warming in the frequency of their occurrence. But researchers say global warming leads to more extreme weather events, including unusually cold spells during winter.

Severe cold waves are not contradictory to global warming, Sun said, but instead, show the climate system is becoming increasingly unstable, and climate forecasting based on regional averages or monthly averages is no longer accurate.

Warming arctic

Sea ice extent has continued to decline, and Arctic temperatures have risen at least twice as fast as global temperatures, possibly even faster, since the year 2000, a recent report by the US National Oceanic and Atmospheric Administration (NOAA) showed.

The 12-month period ended September 2023 marked the sixth-warmest year in the Arctic since records began in 1900, according to NOAA.

In Russia's Norilsk, the world's northernmost city with a sizable permanent population, temperatures will range between minus 10 degrees Celsius and minus 19 degrees Celsius this week, up from minus 20 degrees Celsius to minus 39 degrees Celsius a week ago.

The warmer conditions in Norilsk, nearly 2,500 km north of the nearest Chinese border town, stand in dramatic contrast with the low temperatures in northern China.

In the city of Datong in Shanxi province, its more than three million residents endured temperatures as low as minus 33.2 degrees Celsius on Wednesday. Baoding in neighbouring Hebei province froze at minus 23.3 degrees Celsius, a new record for the industrial city southwest of Beijing.

"When I grabbed the steering wheel on my morning drive to work, I felt like I was grabbing two large icicles," complained Yuan Meng, 27, in Shanxi's provincial capital Taiyuan.

'Temporary blockage'?

Woo Jin-kyu, an official at the Korea Meteorological Administration in Seoul, warned it was "hard to say" if the colder weather could because of a polar vortex weakened by climate change.

It seems more like a "temporary blockage", said Woo.

"A blockage has built up strongly around South Korea as well as Siberia and Mongolia as the airflow from west to east has changed to from north to south," Woo told Reuters.

Chinese forecasters say China's abnormally cold weather may end around Dec 22 in the north and on Dec 23 in central and eastern regions, with temperatures rising to more normal levels by late December.

Complicating China's winter weather forecasting was the onset of the El Nino weather phenomenon.

An El Nino typically leads to a warmer Chinese winter, Sun said.

But the nationwide average changes over the entire winter may not accurately reflect the intensity of extreme events and could even mask the fluctuations within the season, he added.

ALSO READ: Rare snowfall in southern China as deep freeze grips the north

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