The Earth’s warming trends are giving rise to unusual atmospheric behaviors that result in prolonged periods of extreme winter cold and wetness in specific regions, according to a recent study titled “Recent Increase in a Recurrent Pan-Atlantic Wave Pattern Driving Concurrent Wintertime Extremes.” This study, published in the Bulletin of the American Meteorological Society, points to the emergence of giant meanders in the global jet stream, which transport polar air southward, causing extended periods of frigid or wet conditions simultaneously in North America and Europe. Surprisingly, the frequency of these weather patterns has doubled since the 1960s, leading to significant impacts on populations and infrastructure.
Kai Kornhuber, one of the study’s authors from Columbia University’s Lamont-Doherty Earth Observatory, emphasized that while winters are becoming milder on average, this shift is accompanied by increasingly devastating heatwaves during the warmer seasons. However, he stressed that extreme cold remains a significant hazard today and in the foreseeable future.
The jet stream, a high-speed air current circling the Northern Hemisphere, is typically characterized by relatively straight paths, separating polar air from midlatitudes. Nevertheless, it can develop large wobbles, potentially linked to rapid Arctic warming. These wobbles can evolve into symmetrical waves called Rossby waves, and the study suggests that a specific wave pattern known as a wave-4, with four peaks and troughs, is particularly influential during winter. When this pattern locks in place, it triples the chances of extreme cold or wet conditions in the troughs, while the peaks may experience abnormally warm or dry conditions.
An example of the wave-4 pattern occurred in February 2021, causing a severe cold wave across North America, with temperatures plummeting as far south as the U.S. Gulf Coast. Texas experienced record cold, leading to infrastructure failures and widespread power outages, resulting in numerous casualties and extensive economic damage.
Similar wave-4 events also affect Europe, with southwestern Europe and Scandinavia being particularly vulnerable. In January-February 2019, this pattern brought extreme low temperatures to southern France and Sweden while causing flooding in central and eastern Europe by drawing moist air from the Atlantic.
The study reveals that these concurrent waves, which used to occur only once a winter on average 50 years ago, now happen twice a year, indicating synchronization between extreme weather events in North America and Europe.
While the precise mechanisms behind the wave-4 pattern require further investigation, researchers believe it may originate from periodic changes in Pacific oceanic conditions that trigger a global chain reaction. Understanding this mechanism could lead to improved prediction of these extreme winter patterns.
In contrast to the well-established link between climate change and summer heatwaves, the connection between climate change and winter wave patterns is still a subject of scientific debate. Scientists are exploring potential climate-related factors and whether human activities contribute to these extreme events.
In summary, the study underscores the increasing occurrence of synchronized extreme winter weather events in North America and Europe, driven by complex atmospheric patterns, and highlights the need for further research to better comprehend and predict these phenomena in the context of a changing climate.
Source: Columbia Climate School