This winter’s extreme cold snaps, explained

Bitter cold is once again wrapping its icy fingers across the United States, extending the frigid start to the new year.

The weather this week has sent freezing temperatures all the way down to the Gulf Coast. A winter storm warning is in effect for southeast Louisiana, bringing upward of 8 inches of snow. New Orleans saw its first snow in 15 years. Ice and snow have frozen pipes, triggered power outages, and led to road closures around Houston. Florida is also receiving snow in the panhandle.

This stretch of chilly weather comes as a bookend to one of the hottest years on record, and while it’s freezing North America, the origins of this cold actually lie in the Arctic.

There’s evidence that — because of climate change — cold Arctic air may be more likely to break containment in the northernmost reaches of the planet and escape southward, bringing frigid temperatures to lower latitudes like the continental United States.

It may seem counterintuitive, but the fact that global average temperatures are rising does not preclude bouts of cold, and for some Arctic-driven storms, it could exacerbate them. Scientists are examining the mechanisms connecting humanity’s insatiable appetite for fossil fuels, the far north, and winter storms. They’re revealing a complicated picture that shows some of the most profound consequences of climate change occur in the chilliest parts of the planet and during the coolest times of year.

As average temperatures rise rapidly, their effects are manifesting in surprising ways, but with more observations and better forecasting tools, winter storms don’t have to be so deadly and destructive.

There are a couple key mechanisms behind chills like Winter Storm Blair. One is the polar vortex, a spinning band of strong, cold wind that is normally confined to 10 to 30 miles above the North Pole. The polar vortex picks up strength during the winter and tends to stay circular, but because of waves in the atmosphere, it can occasionally split into multiple swirls or deform into an oblong shape that reaches outside the Arctic.

The other factor is a jet stream known as the polar jet. This is a band of air blowing west to east at speeds of up to 275 miles per hour at altitudes between 4 and 8 miles above the Earth’s surface.

When the polar jet is strong, it forms a well-defined ring around the Arctic and holds the icy air in place. When it weakens, it wobbles and forms a flower or clover shape when viewed from directly above the North Pole. Within those lobes, cold Arctic air spills over landmasses like Asia and North America.

Disruptions in the polar vortex can combine with deviations in the polar jet, leading to more cold air reaching even further south.

Such Arctic spillovers, though, have occurred naturally in the past. How does global warming play in? Jennifer Francis, a senior scientist at the Woodwell Climate Research Center, co-authored a review article published in December looking at the body of research trying to answer this question.

The key fact is that while Earth is warming on average, the Arctic is warming up to four times faster than the planet as a whole, a phenomenon called Arctic amplification. That has important knock-on effects.

One is that a warmer Arctic means there is a weaker temperature gradient between the Arctic and its surrounding regions. Francis explained that the steep difference between Arctic and sub-Arctic temperatures is what powers the polar jet in the first place, so as the north begins to feel more like the rest of the planet, the jet gets weaker, making its frigid air more likely to meander across the Northern Hemisphere — and causing more extreme winter storms like Blair.

At the same time, the planet’s oceans have warmed to extraordinary levels in recent years, and some of the planet’s waters, such as the North Pacific Ocean, remain unusually balmy. That’s pushing tropical air further north, bending the jet stream northward over the Pacific and southward over North America.

The loss of sea ice in regions of the Arctic due to warming also has the potential to reshape the polar vortex in ways that lead to more chilly air reaching further south.

Francis and her co-authors acknowledge that there’s a lot of uncertainty in quantifying exactly how much human-caused warming is influencing periods of severe cold. It’s also unclear precisely how this will proceed as the planet keeps heating up.

The effects of warming don’t scale linearly, especially in the Arctic, and there are a lot of complicated feedback mechanisms that researchers are still trying to map out. Melting reflective sea ice, for example, yields to a dark, heat-absorbing ocean that can further melt more ice.

There are also researchers who aren’t convinced that climate change has had a discernible role in recent cold snaps, or that they’ll become more common as global average temperatures rise. One study published last year using climate models and historical records reported that the main way we can see human influence on sudden periods of severe cold is that they aren’t as cold as they used to be. The paper found that cold extremes are warming up faster than average wintertime temperatures in North America.

Scientists generally agree that winters are heating up on average and are warming up faster than summers. Despite this, dangerous winter weather will still, on occasion, spill over from the Arctic. “Even though the Arctic is warming, it will still be frigid during winter for a very long time because it has no sunshine for six months straight,” Francis said in an email. “There will still be plenty of cold air there to feed into cold spells when the jet stream takes a big dip southward.”

Researchers also highlight that the dangers from severe cold waves come not just from the temperature but from how well people are prepared to cope with them. A cold snap can prove deadly if it grips an area that rarely sees such severe chills, as when Winter Storm Uri froze Texas in 2021 and killed 246 people. The threat is amplified when there’s little advance warning.

On this front, there’s a bit of warm comfort in this icy weather. Forecasters are getting a better handle on the warning signs of cold spells. Scientists detected the polar vortex gathering strength last month, and meteorologists were warning since last week that intense cold and snow is in store across much of the United States. With further advances in data gathering and new AI forecasting tools, we’ll likely be able to see the bitter cold more sharply in the future and from farther away.

Update, January 21, 10:50 am: This story was originally published on January 7 and has been updated to include the latest very cold weather.