The 'culprit' of the current cold spells in China

The cause of the bitter cold air sweeping into China this month, setting a seasonal low temperature record, may stem from a weakening polar vortex .

Accompanied by winds that prompted the Chinese government to issue its highest warning for gales, a powerful cold front swept north on December 13. The cold air mass quickly headed east, enveloping the capital Beijing in icy conditions and within days, crossing the Yangtze River and bringing rare snowfall to mountainous regions as far south as Guangdong.

Cold winters are common in China. But the significantly lower temperatures and longer duration of the current cold spell suggest there may be a leak in the circular band of cold air that moves around the Arctic , known as the polar vortex, which typically wraps tightly around the North Pole and keeps Arctic air from seeping out and invading lower latitudes.

A man falls on a slope amid snowfall in Beijing, China, December 14, 2023. (Source: Reuters).

The polar vortex is a giant three-dimensional wind ring that circles the North and South Poles during each hemisphere's winter. The winds operate between 10 and 30 miles above the Earth's surface, in the stratosphere. They blow from west to east at sustained speeds that easily exceed 100 mph. In the darkness of the winter night, temperatures inside the polar vortex can easily drop below minus 100 degrees Fahrenheit.

In recent years, meteorologists have blamed the warping of the polar vortex, which travels at bullet train speeds from west to east at altitudes of up to 50 kilometers, for the bitter cold that has gripped North America.

'Over the past 30 years, the Arctic Circle has experienced the fastest period of global warming, known as Arctic amplification , ' said Shao Sun, a climatologist at the University of California, Irvine. 'The warming has led to a weakening of the polar vortex in the Arctic, allowing cold air within the vortex to move southward, contributing to cold waves.'

There is still debate about whether such weakenings of the polar vortex will become more common in the future, and what direct role global warming plays in their frequency. But researchers say global warming is leading to more extreme weather events, including unusually cold winters.

Severe cold spells do not contradict global warming , but instead show that the climate system is becoming increasingly unstable and that climate forecasts based on regional or monthly averages are no longer accurate, Mr. Sun said .

A recent report from the US National Oceanic and Atmospheric Administration (NOAA) found that sea ice extent continues to decline and Arctic temperatures have increased at least twice as fast as global temperatures, possibly even more, since 2000.

The 12-month period ending in September 2023 marks 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 settled population, temperatures will range from minus 10 degrees Celsius to minus 19 degrees Celsius this week, up from minus 20 degrees Celsius to minus 39 degrees Celsius last week.

Warmer conditions in Norilsk - nearly 2,500 km north of the Chinese border - are in stark contrast to the low temperatures in northern China.

In Datong city in China's Shanxi province, more than 3 million residents endured temperatures as low as minus 33.2 degrees Celsius (minus 33.2 degrees Fahrenheit) on Wednesday. Baoding city in neighboring Hebei province froze at minus 23.3 degrees Celsius (minus 23.3 degrees Fahrenheit), a new record for the industrial city southwest of Beijing.

Yuan Meng, 27, who lives in Taiyuan City, the capital of Shanxi Province, complained: 'When I hold the steering wheel to drive to work in the morning, I feel like I'm holding two big icicles.'

Woo Jin-kyu, an official at the Korea Meteorological Administration in Seoul, warned that it was difficult to say whether the weather would get colder if only a weakened polar vortex due to climate change was considered. But it was more like a 'temporary blockage'.

'The blockage has formed strongly around South Korea as well as Siberia and Mongolia as the west-east air flow shifts from north to south,' Mr Woo said .

Forecasters in China said the unusually cold weather in the country could end around December 22 in the north and December 23 in the central and eastern regions, with temperatures rising to normal levels by the end of December. Forecasting China's winter weather is complicated by the presence of El Nino, which typically makes winters in China warmer, Sun said.

However, Mr Sun added that nationwide changes during winter may not accurately reflect the intensity of extreme events and may even mask seasonal fluctuations.

The strength of the polar vortex can vary widely during the winter, and these variations can lead to changes in the strength and position of the 'river' of air that 'flows' in the troposphere below the polar vortex. As the jet stream changes, it affects the movement of weather systems, causing different parts of the world to become warmer or colder, or wetter or drier.