The Paradox of Cold Spells in a Warming World
In the heart of New England, amidst the biting cold of December, a question lingers: "What happened to global warming?" This query, posed by Michael Rawlins, an associate director at the Climate System Research Center, encapsulates a fascinating climate conundrum.
"Global warming is still very much a reality," Rawlins assures us. "However, it doesn't negate the occurrence of extreme cold outbreaks."
Indeed, December 2025 marked a chilling milestone for parts of New England. The region witnessed an early winter snowstorm, followed by relentless blasts of Arctic air, resulting in record-breaking low temperatures. The month culminated in an icy New Year's Eve, with Boston averaging a chilly 31.3 degrees Fahrenheit, the coldest December since 2017.
Yet, paradoxically, 2025 was one of the hottest years on record globally. The relentless burning of fossil fuels continues to drive up global temperatures, surpassing the 1.5-degree Celsius threshold set by nations in a landmark climate treaty.
To unravel this climate mystery, some experts are turning their gaze northward.
Research suggests that the rapid warming of the Arctic could be influencing the polar vortex, a swirling mass of frigid air above the North Pole. As the Arctic warms at a faster rate than the rest of the planet, the ice on the Arctic Ocean is disappearing, potentially causing the polar vortex to weaken or extend southward more frequently.
Further south, the polar jet stream, fueled by the temperature contrast between the Arctic and temperate regions, is also being impacted. As the Arctic warms, this temperature difference diminishes, potentially causing the jet stream to meander and drive extreme weather patterns.
Jennifer Francis, a senior scientist at Woodwell Climate Research Center, first proposed this idea in 2012. Since then, numerous studies have been published, with a consensus emerging that climate change is indeed influencing the jet stream. However, the field is still evolving, and attributing specific cold spells to climate change remains a complex task.
"We're still piecing together the puzzle," Francis explains. "Understanding how these atmospheric interactions work is an ongoing process."
Francis suggests that a marine heat wave in the North Pacific and the lack of sea ice in the Arctic Ocean north of Scandinavia, both exacerbated by global warming, could be influencing the jet stream and driving colder weather in the Northeast. The polar vortex, she says, has been periodically stretching over North America, reinforcing cold spells.
But not everyone agrees with this interpretation. A study by a Dartmouth team, published in June, challenges the idea that the jet stream's recent meandering is unusual. Their analysis of the jet stream's variability since 1901 shows that it was wavier during certain periods of the 20th century than it is today.
"We don't yet have strong evidence that climate change is intensifying these cold snaps and jet stream waviness," says Jacob Chalif, a Dartmouth graduate student and co-author. "At least, not yet."
Another factor in the cooler weather is the current La Niña conditions, characterized by below-average sea surface temperatures across the Pacific Ocean. These climate patterns, which occur irregularly every few years, can also influence regional temperatures.
Ambarish Karmalkar, a geosciences professor, notes that while La Niña winters have brought chillier temperatures in the past, December's La Niña was relatively weak, and the impact on local temperatures is highly variable.
"There's no single variable that explains all the regional temperature variations we experience," Karmalkar emphasizes.
Even as New England warms overall, it will still experience record lows and cold months. A study published in early December reveals that New England has already warmed by more than 4.5 degrees Fahrenheit since 1900, making it one of the fastest-warming regions globally. In Massachusetts, the state has lost about 30 days of snow cover annually since the early 2000s.
"The data is clear: we're warming up," says Stephen Young, a professor of environmental sustainability and lead author of the study.
Michael Iacono, chief scientist at Blue Hill Observatory, highlights that despite the cold December, the year as a whole averaged around 50 degrees, making it the coldest year since 2019. The observatory's climate record, dating back to 1885, shows that the five years preceding 2025 were the warmest five-year period on record.
The cold and dry weather is expected to persist at least through the start of January. However, New England may find some relief later in the month, with forecasters predicting a warmer-than-normal winter for much of southern New England.
So, while the cold spells may be disruptive, they are a reminder of the complex and evolving nature of our climate. As we navigate these challenges, one thing is certain: the conversation around climate change and its impacts is far from over.
What are your thoughts on this intriguing climate puzzle? Feel free to share your insights and questions in the comments below!
