Although the earth heats up through climate change as a whole, in parts of the USA there are increasingly icy winter with extreme snowfall and life -threatening deep temperatures. Climate researchers have now found out which factors contribute to this local extreme weather. Accordingly, two specific patterns of the polar vertebra are responsible for this. You determine when and where a cold slump occurs on the continent. These polar air currents interact in turn with the jet stream and are influenced by the El Niño phenomenon-and ultimately also by climate change.
The global annual temperature increases with climate change. The earth heats up and winter get milder. This also applies to the United States, but only averaged across all states. Because some parts of the country have surprisingly often experience violent cold and snow breakdowns. The last cold extremes in the USA occurred in the winters 2009/2010, 2013/2014, 2014/2015, 2020/2021 and 2024/2025. In February 2021 there was, for example, an icy cold in Montana, in the middle west and in Texas, which cost hundreds of lives. The electricity failed in millions of households. But how does these local cold extracts come about despite global warming?
Shifting the polar vertebra causes winter burglaries
Researchers around Laurie Agel from the University of Massachusetts have now examined this. To do this, they evaluated weather data of the past few years and extracted repeating patterns. They focused on the polar vertebrae: a volume of cold air in the stratosphere, which the Arctic circle over our heads at twelve to 50 kilometers. “The public often hears from the ‘polar vertebrae’ when winter becomes strict, but we wanted to dig deeper and understand how variations within this vertebra have an impact on where and when extreme cold strikes,” said the team.
AGEL and her colleagues identified a total of five specific patterns within the polar vertebra. Two of them are responsible for the cold collapse in the United States. These two atmospheric patterns steer extreme cold from the Arctic into different parts of the country. A flow pattern drives the air from the upper part of the polar vortex towards Westkanada and leads to cold air in the northwest of the USA. The other pattern weakens the upper part of the vertebra and directs it towards the North Atlantic, which leads to cold in the central and eastern parts of the country. Both movement patterns “stretch” not only the upper vertebral section, but also the lower part of the polar vortex, so that it ranges from Asia to North America. Deeper wind bands of the polar jet stream, which rise from cold areas such as Siberia and East Asia, collapse on these layers of air in the stratosphere and are directed back towards the surface of the earth. This distorted and shifted circulation pattern of the arctic air therefore leads to unusual weather and intensive cold on the ground, explains the team.
Cold in the northwest occurs in La Niña phases
The team also found that the northwest of the United States has been experiencing more of these refrigeration since 2015 than other parts of the country. The researchers conclude that the polar vertebrae dynamically changes and has recently been geared towards the west and less often to the east. Striking here: This shift coincides with periods of another climate phenomenon – the El Niño/Southern Oscillation (EnSO). As the team stated, cold waves in the northwest of the United States appear more in cold La Niña phases of the ENSO. The air circulation of the ENSO is closely connected to the jet stream and also an important driver of global weather, especially in lower widths. Agel and its colleagues emphasize how exactly the ENSO affects the polar vortex in the higher stratosphere in the higher stratosphere.
Knowing how stratospheric flow patterns affect the weather in the underlying troposphere could improve the weather forecasts in the long term. “The location and movement of temperature anomalies can be predicted based on the strength of the polar vertebra,” explains the team. Cities, farmers and operators of electricity networks could then better prepare for winter extremes. At the same time, it helps to understand how climate change affects these relationships. Because the global warming has been shown to slow down the wind bands of the jet stream and thus ensure that low pressure areas linger longer in one place. There are also forecasts that La Niña phases could occur more frequently due to climate change. If this is confirmed, the cold waves in the United States could continue to increase. “Climate change not only means that the earth warms up everywhere.
Source: Laurie Agel (University of Massachusetts) et al.; Science Advances, Doi: 10.1126/Sciadv.adq9557
