Are stratospheric polar vortex disruptions what they seem?
A weak or distorted stratospheric polar vortex (SPV) is often associated with severe winter weather in Northern Hemisphere continents. Traditional metrics of the SPV state, however, may conflate influences from both the stratosphere and the troposphere below, obfuscating attribution of weather extremes. In a new paper, published this month by Climate Dynamics, researchers present a new method that more clearly separates variations in the two atmospheric layers and their contributions to severe winter weather.
Depending on your feelings toward cold and snow, the headline “The Polar Vortex is Coming!” may instill dread or delight. The Polar Vortex first entered dinner-table conversations during the extreme winter of 2013/14, the coldest North American winter of the 21st century, and has since been used—often incorrectly—as shorthand for any cold or snowy spell. The polar vortex is a pool of frigid air encircled by strong westerly winds that sits high above the polar regions during winter only, and normally it has little influence on weather at the surface. But when it becomes disrupted from its typically circular shape—either stretched to an oblong, split into separate swirls, or greatly weakened—extreme winter weather can ensue, including severe cold, snow, and even winter heat waves.
One of the ways scientists track the behavior of the stratospheric polar vortex is to monitor the height of a constant pressure surface that exists within the stratosphere. Pressure decreases at higher altitudes because there are few air molecules above that level. The height of a pressure surface bulges and shrinks depending mainly on the temperature of the air below it: warmer air expands and cooler air contracts. Height fluctuations of a level in the stratosphere, then, are caused by temperature changes in the whole column of atmosphere below that level, not only in the stratosphere. Disruptions to the SPV detected using pressure heights, therefore, may be misleading as to their cause.
“As I explored the role of stratospheric disruptions on extreme winter weather, it occurred to me that there might be a better way to measure those disruptions,” said Dr. Jennifer Francis, Senior Scientist at Woodwell Climate Research Center and lead author. “Focusing on the stratosphere itself rather than the whole atmospheric column helps separate the influences from the two layers, which often behave independently.”
The authors analyzed the thickness of a layer in the stratosphere using an AI-based approach to identify representative patterns in the SPV, including various types of disruptions.
“The new metric revealed an increased occurrence of strong and abnormally cold SPV patterns,” added co-author Natasa Skific, Researcher at the Woodwell Climate Research Center. “This is different from findings in earlier studies based on pressure heights. Our findings make sense because higher concentrations of greenhouse gases cool the stratosphere, causing a stronger SPV.”
Paper co-author Dr. Judah Cohen, Research Scientist at MIT Parsons Lab and Director of Seasonal Forecasting at Atmospheric and Environmental Research, noted the previously underappreciated common occurrence of vortex stretching, which often contributes to cold spells in the U.S. and central Eurasia.
“The results of our study fit with other work highlighting the importance of stretched-vortex states on severe winter weather. Our new metric helps isolate the stratosphere so we can better understand its dynamics and connections with weather extremes, atmospheric blocking, and amplified Arctic warming.”
Fire on ice: The Arctic’s changing fire regime
The number of wildland fires burning in the Arctic is on the rise, according to NASA researchers. Moreover, these blazes are burning larger, hotter, and longer than they did in previous decades.
These trends are closely tied to the region’s rapidly changing climate. The Arctic is warming nearly four times faster than the global average, a shift that directly impacts rain and snow in the region and decreases soil moisture, both of which make the landscape more flammable. Lightning, the primary ignition source of Arctic fires, is also occurring farther north. These findings are detailed in a report published in 2025 by the Arctic Monitoring and Assessment Programme (AMAP), a working group of the Arctic Council.
Trump is leaving UN environmental bodies. What that means for the climate
On Wednesday night, President Trump announced that the U.S. would be withdrawing from the United Nations Framework Convention on Climate Change (UNFCCC), a landmark global treaty that sets a legal framework for international negotiations to address climate change.
The move comes after the Trump Administration asked the State Department to review the country’s involvement in various international organizations last February. The result is that the president has now withdrawn the United States from a total 66 international organisations, including 31 United Nations entities. Other groups included U.N. Oceans, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, and the International Renewable Energy Agency.
On January 5, Woodwell Climate submitted public comment to the U.S. Environmental Protection Agency’s (EPA) and U.S. Army Corps of Engineers’ (Army Corps) proposed rule to update the definition of “Waters of the United States” (WOTUS).
As a result of climate change, flood risk is projected to increase for Leominster. The probability of the historical 100-year rainfall event, a useful indicator of flood risk, is expected to almost triple by mid-century and be more than five times as likely by the end of the century. Streamflow for the North Nashua River is also estimated to rise throughout this century with an increase of 12.2% by 2050 and an additional 12.5% by 2080. Both increases in streamflow and heavier rainfall will translate into greater flood depths and extent for Leominster. The vulnerability of Leominster’s stormwater system was evaluated under the present and future 100-year rainfall event. Here we present our findings on extreme precipitation and flooding to help Leominster in its plans to create a more resilient future for all residents.
As a result of climate change, flood risk is projected to increase for New Bedford. The probability of the historical 100-year rainfall event, a useful indicator of flood risk, is expected to double by mid-century and be more than three times more likely by the end of the century. Heavier rainfall will translate into slightly greater flood depths and extent for New Bedford. Making changes to the land elevation and culverts will help alleviate some of the flooding near Terry Lane and Chaffee Street. Here we present our findings on extreme precipitation and flooding to help New Bedford in its plans to create a more resilient future for all residents.
Mass. home insurer of last resort sees spike in enrollment
Combination of growing climate risks and inflation likely led to roughly 15,000 new policies added to FAIR Plan in fiscal year 2024
Don’t pull the fire alarm yet, but new data on home insurance in Massachusetts is turning heads across the industry.
Massachusetts enrolled more than 173,000 policies in its insurer of last resort, known as the FAIR Plan, in fiscal year 2024 — marking the first year-over-year increase for the insurer since 2017 and its largest single-year jump since 2007. In fiscal 2023, the FAIR Plan enrolled 158,660 policies.
Continue reading on Commonwealth Beacon.
A message from President & CEO Dr. R. Max Holmes
A few weeks ago, as the temperature here in Falmouth really dropped for the first time, I pulled out my winter coat. In the pocket, I found a folded copy of comments I made at a Stand Up for Science rally back in March. It was a stark reminder of just how much has happened—and how far we have come—this year.
Here at Woodwell, our days are long and full. Attempting to recall any year’s efforts and events can be head-spinning. This year, there was an added intensity, as everything we did felt like it was happening while riding a roller coaster. And yet, as we approach the end of 2025, I am certain that our organization and our work are stronger and more essential than they were a year ago.
That does not diminish the climate policy setbacks—truly immense—we have seen at the federal level here in the U.S. Withdrawal from the Paris Agreement and the UN climate negotiation process, efforts to roll back the Endangerment Finding, the dismantling of federal climate science programs, the end of IRA incentives for renewable energy and electric vehicles, and a host of regulatory changes that threaten clean air and water—these are just a handful of the moves whose damaging impacts will be felt ever more acutely as we move forward.
Federal actions have also directly impacted Woodwell’s operations, from the loss of (a small number of) government grants and collaborations to concerns about future funding priorities and criteria. For a time, even the security of our non-profit status was in question. The first third of this year felt like an unrelenting assault. Uncertainty, even fear, was a constant theme. But as the months have passed, the frenetic pace has eased and we have shifted from crisis footing to a risk-aware but forward-looking stance.
Through it all, Woodwell’s experts have stood strong and spoken up for science—whether in public comments on proposed rule changes or in personal reflections shared at a Moth-style story slam. We have shared our strength in mapmaking with Indigenous communities around the globe—from women’s firefighters in the Amazon, to Alaska Native villages, and traditional reindeer herding communities—so that they can leverage the power of geospatial data. We have supported the launch of an innovative new international mechanism to fund tropical forest conservation, the Tropical Forests Forever Facility. And I, along with more than a dozen Woodwell experts, were among those attending COP30 and making sure the rest of the world knows not all Americans have turned away from the UN climate agenda. Indeed, Woodwell’s delegation contributed to some of the top items, from forest finance and Indigenous leadership, to increasing ambition and monitoring resilience.
Onward,
