For over a century, the polar jet stream has played a crucial role in shaping weather patterns across the Northern Hemisphere, yet its long-term behavior remains surprisingly understudied until recently. Studies have often focused on the period following 1979, the dawn of satellite-era observations, leaving much of the jet stream’s earlier history a mystery. However, a groundbreaking study conducted by researchers at Dartmouth College has leveraged advanced machine learning techniques to reconstruct a 125-year timeline of the jet stream’s wintertime variability, revealing new insights that challenge prevailing narratives about climate change and atmospheric dynamics.
The investigation, published in the journal AGU Advances, confronts the widespread assumption that recent dramatic waviness and volatility in the polar jet stream are primarily consequences of anthropogenic climate change. By analyzing extensive historical climate datasets using novel statistical tools, the Dartmouth team has uncovered evidence that the jet stream’s erratic behavior is not unprecedented. Indeed, periods of pronounced waviness, with far-reaching impacts on weather, have occurred sporadically over the last century, independent of the direct influence of global warming.
Under normal conditions, the polar jet stream acts as an atmospheric boundary, flowing west to east along the northern border of the United States, modulating the distribution of cold Arctic air and warmer southern air masses. When the jet stream’s path forms large, meandering waves—sometimes described as “wavy” or “wavy patterns”—cold Arctic air can plunge deep into lower latitudes, precipitating extreme cold snaps and intense winter storms even in regions unaccustomed to such conditions. The recent spike in extreme winter weather events has been linked by some climate scientists to these persistent and amplified undulations in the jet stream, presumed to be fueled by a warming Arctic and changing atmospheric dynamics.
Contrary to this prevailing interpretation, the Dartmouth study reconstructs jet stream behavior dating back to 1901 through machine learning models trained on long-term temperature, pressure, and wind data, far preceding the satellite record. This extended chronology reveals that we are currently in what the authors characterize as the latest wavy phase in the jet stream’s natural cycles. Intriguingly, some previous episodes exhibited even greater amplitude and volatility, including a pronounced wavy period spanning from the 1960s to the 1980s, which played a pivotal role in the climatic anomaly known as the “warming hole” in the southeastern United States.
The "warming hole" refers to a counterintuitive 30-year interval when average winter temperatures in parts of the U.S. Southeast dropped by approximately 2 degrees Fahrenheit, contrary to the overall hemispheric warming trend. This cooling phase bewildered climatologists for years, with various hypotheses attempting to decipher its cause. The new research confirms that enhanced waviness in the jet stream led to repeated incursions of cold Arctic air into the region, establishing a persistent pattern of cooler winters well before the modern era of pronounced climate change impacts.
Lead author Jacob Chalif, a graduate student working under Professor Erich Osterberg, explains that the findings complicate the simplistic narrative linking jet stream instability directly to global warming. “The jet stream was frequently just as wavy as it is today, if not more so, prior to the significant influence of climate change,” Chalif states. “This temporal context allows us to reconsider how we interpret modern atmospheric variability framed against a much longer historical baseline.”
Professor Osterberg, who directs Dartmouth’s Ice, Climate, and Environment Lab, emphasizes that while climate change undeniably intensifies extreme winter weather events through other mechanisms—such as increased atmospheric moisture leading to heavier precipitation—its role in modulating jet stream waviness may not be as direct or significant as once believed. Instead of attributing more erratic jet stream behavior solely to human-induced climate factors, researchers must explore alternative processes influencing these atmospheric patterns.
The broader implications of the Dartmouth study urge a reframing of how climate scientists relate jet stream dynamics to extreme weather in the context of global warming. Rather than focusing exclusively on the jet stream’s path alterations, research may increasingly prioritize the thermodynamic factors associated with a warmer atmosphere. Enhanced atmospheric moisture content and energy fluxes may prove to be more critical drivers of intensified storms, including hurricanes and winter blizzards, than the amplitude of jet stream waves alone.
Understanding the natural variability of the jet stream presents a significant advancement in climate science’s capacity to interpret past, present, and future weather phenomena. Because satellite observations began in 1979 coinciding with one of the more wavy phases in jet stream history, previous research may have overstated the extent to which current jet stream behavior deviates from long-term norms. This study’s rigorous multi-decade reconstruction fills a vital data gap, offering a more nuanced perspective on atmospheric variability before and after the advent of satellite-era climate monitoring.
Additionally, this research illuminates the complexity of what climatologists term “climate chaos”—the vast web of interacting influences shaping weather on daily, seasonal, and decadal timescales. As Chalif notes, daily weather is affected by a tapestry of forces, many of which remain poorly understood or difficult to predict. The long-term reconstruction of jet stream variability enriches this understanding by contextualizing recent patterns within broader, historically recurring cycles.
Moreover, the study helps clarify the link between jet stream waviness and significant weather events such as the polar vortex. Often referenced in media as the culprit behind sudden Arctic blasts, the polar vortex itself can be influenced by jet stream configurations that channel frigid polar air into mid-latitudes. Nonetheless, this new research suggests that the frequency and severity of such incursions have fluctuated naturally over the past century, sometimes independently of anthropogenic climate drivers.
Co-author Trevor Partridge, a former Dartmouth PhD student now with the U.S. Geological Survey, previously correlated jet stream patterns with the warming hole phenomenon. His continued involvement in this study further substantiates the connection between jet stream dynamics and regional climate anomalies, underscoring how shifts in jet stream waviness can establish temporary climate regimes that defy general warming trends.
Ultimately, these findings call for a recalibration of research priorities within climatology and meteorology. They urge scientists and policymakers to anticipate extreme weather through multifaceted lenses that appreciate both natural cycles and anthropogenic influences. As the climate continues to warm, the atmospheric system’s response may be less straightforward than linear cause-effect assumptions suggest, demanding sophisticated analyses that disentangle layered climatic processes.
In a rapidly evolving climate context, the Dartmouth team’s contribution offers both clarity and caution. While global warming remains an undeniable force reshaping Earth’s climate, this study emphasizes the necessity of integrating long-term historical data to avoid misinterpreting transient phenomena as unprecedented trends. With continued advancements in machine learning and data analytics, future research promises even more detailed reconstructions of atmospheric behavior, empowering society to better prepare for the full spectrum of climate-induced challenges ahead.
Subject of Research: Not applicable
Article Title: A Wavier Polar Jet Stream Contributed to the Mid‐20th Century Winter Warming Hole in the United States
News Publication Date: 26-Jun-2025
Web References: http://dx.doi.org/10.1029/2024AV001399
References: Chalif, J., Osterberg, E., Partridge, T., et al. (2025). A Wavier Polar Jet Stream Contributed to the Mid‐20th Century Winter Warming Hole in the United States. AGU Advances. DOI: 10.1029/2024AV001399
Image Credits: Jacob Chalif/Dartmouth
Keywords: Climate change, Anthropogenic climate change, Climate change effects, Environmental issues, Extreme weather events, Storms, Weather, Seasonal changes, Winter season, Climate data, Climatology, Climate modeling, Machine learning, Meteorology, Weather simulations, Physical sciences, Atmospheric science, Earth systems science, Planet Earth, Earth sciences
