- Climate
Cold snaps during global warming are not actually a paradox, here’s why
Why do cold snaps persist if the Earth is warming? This question has popped up in various forms online, especially on social media. Climate contrarians often use it as a rhetorical question to make the false claim that ‘global warming must not be happening if we still experience cold weather’.
Others may ask this question out of genuine curiosity – after all, it might be confusing to hear that the planet is warming if you are shivering in a cold spell.
But does anything actually prevent global warming and cold snaps from coexisting? Not at all. Cold snaps (short periods of very cold weather) occur when there are large southward dips in the jet stream – strong winds 5 to 7 miles (8 to 11 kilometers) above Earth’s surface that blow west to east (Figure 1).
It’s clear that global warming has not stopped this process because climate scientists know for certain that Earth is warming and that cold snaps are still occurring. But that doesn’t answer the more interesting question of why.
The simple answer is that global warming does not stop Earth’s seasons from changing – thus allowing for winter weather – nor does it stop atmospheric circulation patterns that drive weather fluctuations. To dig deeper on this, we will explore what global warming is and – very importantly – what it isn’t, and how this ties into cold weather and cold snaps.
Later, we will share comments Science Feedback received from five climate scientists on this topic and explore a hotly debated theory surrounding it.
Main Takeaways:
- Global warming is causing winters to get warmer, and making cold snaps less frequent or less intense over most land areas globally since 1950;
- Global warming does not mean that all cold weather should suddenly stop happening – just that global average temperatures measured around the world are rising;
- Cold weather and cold snaps are part of Earth’s natural climate variability and are not evidence against global warming
- Cold snaps occur when there is a dip in the jet stream (fast west-to-east flowing air currents 5 to 7 miles up) that brings cold air from the Arctic to lower regions like the U.S. or Europe; and,
- Rapid warming in the Arctic is outpacing the rate of warming at a global scale; though hotly debated among climate scientists, some think this is influencing the jet streams in a way that increases cold extremes in mid-latitude regions (like the U.S.).
Global warming is making winters warmer, but that doesn’t mean cold weather will suddenly disappear
To understand why global warming doesn’t just stop cold weather from happening, it’s important to know both what global warming is and what it isn’t.
The term ‘global warming’ does not imply that ‘everywhere is hot all the time’. Instead, it means that average global temperatures – measured from locations across Earth – have risen over the long term (typically decades or more). (See our past review on climate vs. weather).
With the massive scale of our planet, this can be tricky to visualize. To simplify this, imagine heating up food. If you stick a large ham in the oven, for example, the ham is not instantly hot. Parts of the ham remain cold, while other spots heat up more quickly.
By the same token, cold temperatures occurring somewhere on Earth does not mean the Earth is not warming overall. Moreover, Earth is far more complex than a piece of food in an oven – it is a massive rotating planet with large circulating systems like oceans and atmospheric layers that move and store heat around Earth.
Given the complexity of our dynamic planet, scientists look at average global temperatures over decades or more. Looking at long-term averages in this way allows climate scientists to identify clear climate trends that might otherwise be obscured by short-term weather fluctuations (over days, weeks, or months). And what do they find?
Evidence from decades of research shows – without a shadow of doubt – that Earth has been warming since the industrial revolution in the late 1800s[1]. This recent warming has been driven by human activities – such as burning fossil fuels – which have increased the greenhouse gases like carbon dioxide (CO2) in our atmosphere[1]. These greenhouse gases increase global temperatures by trapping outgoing energy/radiation (heat) that would otherwise escape to space.
This process is known as the greenhouse effect – something we’ve covered in depth in past reviews – and it creates an energy imbalance in Earth’s climate, causing it to warm over time. So, if the planet is warming, why do we still experience cold weather? Put simply, global warming does not stop seasons – like winter – which are driven by Earth’s orbit and tilt relative to the sun.
Seasons occur because Earth’s axis of rotation is tilted relative to the sun (see figure below). This tilt causes Earth’s northern or southern hemisphere to be closer to the Sun at different periods of Earth’s orbit. Whichever hemisphere is tilted toward the sun will experience summer, while the other experiences winter.
Diagram showing why Earth’s tilt allows the northern and southern hemispheres of our planet to experience seasons differently as we orbit the sun. During the part of Earth’s orbit when the northern hemisphere is tilted toward the sun (as shown above), it will be summer in the northern hemisphere, and winter in the southern hemisphere. And vice versa when the northern hemisphere is tilted away. Adapted from source: The Conversation
Although winters still occur in a warming climate, that doesn’t mean they aren’t changing. As explained by the Intergovernmental Panel on Climate Change (IPCC), winters in general are getting warmer, and cold snaps have become less frequent or less intense over most land areas globally since 1950[1].
Figure 2 below from IPCC’s Sixth Assessment Report shows that the annual coldest temperature in most land regions has increased (i.e., gotten warmer) between 1960 to 2018[1].
Looking specifically at mid-latitude regions in the northern hemisphere – an area that some claim has seen an increase in cold extremes – a 2024 peer-reviewed paper in Science Advances found a marked decrease in intensity of cold temperatures from 1971 to 2022[2]. This trend is shown in Figure 3 by a decrease in the number of very cold days in winter over time (graph B) and by a warming trend of the coldest days each winter (graph A).
(B): The number of days in winter where temperatures fell below the fifth percentile threshold (from 1971 to 2022), shown as ‘TM5p’ above. The downward trend in this data (black line) represents a decrease in extreme cold days.
Note that there is a very close match in both graphs between ERA5 (black line) – which has been shown to capture extreme temperatures well – and the other data (colored lines), showing good consistency between the data sets. Source: Blackport et al. (2024)[2]
Despite winters getting warmer, short periods of extreme cold (cold snaps) can still hit some regions quite hard. But this is no surprise to climate scientists. As Dr. Andreas Schmittner, Professor of Earth, Ocean, and Atmospheric Sciences at Oregon State University, explained to Science Feedback:
Andreas Schmittner
Professor, Oregon State University
“Cold snaps have always occurred and will continue to occur even as the globe is warming. This is part of natural climate variability.”
So what are the actual reasons for these cold snaps, and does global warming play a role?
In the next section, we will share comments we received from five climate scientists about the factors driving cold snaps and why there is still debate surrounding global warming impacts on the polar vortex and jet stream.
Cold snaps are part of Earth’s natural climate variability and can still occur while Earth warms
Cold snaps – likely due to their extreme nature – seem to trigger questions about global warming.
A question about cold snaps and global warming was even brought up in a recent NBC segment that went viral on Facebook. Al Roker, one of NBC’s weather presenters, claimed: ‘Global planet warming allows some parts of the U.S. to be colder than usual because as warm air moves into the arctic, it weakens the polar vortex and allows cold air to move south’. The video gathered over 420,000 views and sparked many debates in the comments section – most of which were started by climate change deniers.
Although the persistence of cold snaps in a warming climate is not a surprise to climate scientists, Roker’s specific claim tying in Arctic warming actually touches on a hotly debated topic among climate scientists.
To learn more about cold snaps, we reached out to several climate scientists. One of whom was Dr. Jennifer Francis, Senior Scientist at the Woodwell Climate Research Center, who researches how warming in the Arctic impacts weather patterns in mid-latitude regions. Francis explained:
Jennifer Francis
Senior Scientist, Woodwell Climate Research Center
“A winter cold spell is always caused by a large southward dip (aka trough) in the jet stream”
These dips naturally occur when the jet streams weaken and become wavier, allowing cold air to flow down from the Arctic into mid-latitude regions like the U.S., bringing exceptionally cold temperatures with it. This concept is depicted in Figure 4 below.
This is a well-known phenomenon among climate scientists and occurs as part of Earth’s natural climate variability. However, research papers over the last 12 years have argued that rising temperatures in the Arctic – which has been warming four times faster than the global average since 1979[3] – are leading to a wavier jet stream and thus a higher likelihood of cold extremes in mid-latitude regions in the northern hemisphere.
This is the root of Roker’s recent claims, but it is also a hotly debated topic among climate scientists. While Roker portrayed a mostly-accurate picture of why cold snaps generally occur, some key context was missing. When Science Feedback asked about Roker’s general claim, Francis explained:
Jennifer Francis
Senior Scientist, Woodwell Climate Research Center
“Yes, he’s basically correct, though the ‘polar vortex’ he refers to is actually the jet stream. Our research has shown that when the Arctic is abnormally warm during winter, North America and Eurasia tend to be colder than normal. The true polar vortex is in the stratosphere and exists only in winter. When it becomes disrupted from it’s typically circular shape, it can intensify cold spells over the continents [see link here][4]“
Beyond a minor terminology mix-up, the main issue with Roker’s claim is that it connects these cold snaps to rapid Arctic warming – and, thus, global warming. In reality, these jet stream dips happen as part of Earth’s natural variability, with or without global warming. Climate scientists are studying ways in which current global warming may be affecting certain behaviors of the jet stream, but the verdict isn’t out yet.
As explained by Dr. Adam Sobel, Professor of Applied Physics and Applied Mathematics and of Earth and Environmental Sciences at Columbia University:
Adam Sobel
Professor, Columbia University
“Roker is not representing a scientific consensus. While there have been studies for around 12 years arguing that arctic warming weakens the tropospheric polar vortex and that this leads to an increased probability of cold extremes in midlatitudes, these studies have also been strongly challenged.”
This was the general sentiment from several of the climate scientists we spoke with. However, one of the scientists Science Feedback contacted, Dr. Francis, believes that although jet stream troughs occur naturally, global warming could be increasing their waviness through the rapid – and disproportionate – Arctic warming we noted earlier. Francis explains:
Jennifer Francis
Senior Scientist, Woodwell Climate Research Center
“These [jet stream] troughs occur naturally, but recent studies suggest jet stream waviness is increasing during winter, allowing cold spells to become more persistent and extend farther south. Disproportionate Arctic warming is one likely reason for this increased waviness, but other factors such as intensifying ocean heat waves and more frequent disruptions of the stratospheric polar vortex are also playing a role.”
When Science Feedback asked if any evidence suggests that human-caused global warming is directly causing jet stream waviness to increase, or if it is more loosely connected, Francis explained:
Jennifer Francis
Senior Scientist, Woodwell Climate Research Center
“I would say that our recent review paper provides convincing evidence for causal mechanisms contributing to this linkage. Natural variability is always large in winter, which makes it difficult to assess causes of any particular cold spell […] I wholly agree there is still much we don’t understand about connections between rapid Arctic warming and winter weather extremes (not only cold spells), but I think there are two fronts we addressed in this new paper that shed light on the topic.”
Francis explained that rapid warming in the Arctic is reducing the north-south temperature difference (temperature gradient), which makes ‘blocks’ – high-pressure areas in the atmosphere that are nearly stationary – more likely to form. “These blocks are like eddies in a river that become separated from the main flow and can swirl in one place for a long time,” Francis explains. “A favored location of blocks is near Greenland, which is associated with upstream troughs in the jet stream that create cold spells.”
The second piece of evidence comes from the fact that the Barents/Kara Seas area (north of western Russia) is warming faster than most places on Earth – Francis explains*:
Jennifer Francis
Senior Scientist, Woodwell Climate Research Center
“As this region warms faster than almost anywhere on Earth, it is sending wave energy upward that can “topple” the vortex, similar to poking a spinning top with your finger. If you poke it hard enough for long enough, eventually the spinning top will wobble. The same thing is happening to the vortex — it is more likely to become elongated or even split as this region warms. And we know when the vortex is disrupted, it tends to send its cold air southward where it can intensify cold-air outbreaks.”
*Note: For more details about this evidence, see Francis’ full response in the Scientists’ Feedback section at the end of this article.
Other climate scientists argue that the theory has not yet been validated. Regarding the possibility that a weaker and wavier jet stream could lead to more hot and cold extremes, Dr. Michael Wehner, Senior Scientists at the Lawrence Berkeley National Laboratory, explained:
Michael Wehner
Senior Scientist, Lawrence Berkeley National Laboratory
“that change has not been observed in a statistically significant sense. So while it is an interesting theory, it has yet to be validated […] In my opinion, the theory is interesting and probably correct. But a climate change signal has not risen above the noise of natural variability.”
Conclusion
Global warming has not stopped all cold weather and cold snaps from happening, but this isn’t a surprise to climate scientists. Since 1950, on a global scale – and over most land areas – winters have been getting warmer as global temperatures have risen, and cold snaps have become less frequent or intense. Despite global warming, seasons will continue as part of Earth’s natural cycle (a result of Earth’s tilt and orbit), and along with it, hotter and colder periods (summer and winter).
Cold snaps are also part of Earth’s natural climate variability, but they have decreased at a global scale in frequency or severity as the planet has warmed. Cold snaps in the northern hemisphere can occur with or without global warming, as disruptions to the polar vortex (cold air currents circling high above the Arctic) cause the jet stream (fast west-to-east flowing winds at lower altitudes) to dip southward, carrying cold air to mid-latitude regions (like the U.S.). Some have argued that global warming has affected the jet stream in a way that is making cold extremes in these regions more likely, but the theory is still hotly debated among climate scientists.
Scientists’ Feedback
Questions to scientists from Science Feedback:
- Does the claim made by Al Roker accurately describe why some parts of the U.S. can experience cold periods while the planet is overall warming? Or is the ‘weakening/more wavy polar vortex from arctic warming’ he describes just one mechanism among others that might cause this to occur?
- Is there sufficient evidence that anthropogenic climate change – especially in the arctic region – has affected the polar vortex in a way that causes (not just correlates with) cold weather anomalies in lower latitudes (e.g., the U.S.)? Or could this mechanism – if there is good evidence for it – fall within natural variability?
- Are climate scientists confident about how anthropogenic climate change has impacted (or will impact) winter temperatures?
Adam Sobel
Professor, Columbia University
1 & 2. My answer is no, Roker is not representing a scientific consensus. While there have been studies for around 12 years arguing that arctic warming weakens the tropospheric polar vortex and that this leads to an increased probability of cold extremes in midlatitudes, these studies have also been strongly challenged. In my view the challengers are right and I believe most scientists with expertise in atmospheric dynamics (though not all) agree. The observational evidence for increased mid-latitude cold extremes due to arctic warming is weak, and the dynamical arguments are as well. Climate models, to the best of my knowledge, do not do it either. So in answer to your third question, the answer is yes, climate scientists are confident that anthropogenic climate change has made winter temperatures warmer.
3. Despite global warming, the arctic is still colder than midlatitudes, and that will remain true. The “polar vortex” is really the jet stream, which roughly corresponds to the (moving) boundary between relatively warmer and colder air masses. So yes, when the jet dips south in such a trough, it brings relatively cold air behind it.
Michael Wehner
Senior Scientist, Lawrence Berkeley National Laboratory
There will always be winter. And sometimes it will be extremely cold compared to the “new normal” that could be attributed to the “polar vortex”. The question that remains is “are those periods extremely cold compared to the “old normal”. That is the part [of] the open research question.
So Mr. Roker is correct that despite global warming there will be periods of relative cold. The key word being relative. But tying increases in extreme cold temperature outbreaks to changes in the polar vortex is premature.
Yes, of course, The world will continue to experience cold periods (called winter…). But winter seasons have gotten warmer including the coldest night of the year. See the middle panel of figure 11.9 of the IPCC AR6 WG1 report[1]
1. The weakening of the winter jet stream (aka polar vortex) is occurring. And it has been suggested that a weaker jet stream is a wavier jet stream which could lead to more frequent hot and cold extremes through atmospheric blocking and other atmospheric circulation phenomena. However, that change has not been observed in a statistically significant sense. So while it is an interesting theory, it has yet to be validated. Note that opinions are strong on this issue. In my view, this is still an active research area See cross chapter box 10.1 of the IPCC AR6 WG1 report at https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-10/
2. In my opinion, the theory is interesting and probably correct. But a climate change signal has not risen above the noise of natural variability.
3. I think we are confident that average winter temperatures are getting warmer. And the coldest night of the year is also warming. But the question about very rare cold winter temperatures remains open in my opinion.
I would also add that because winters are getting warmer, people are not as used to cold temperatures like they were in the past. So cold temperatures that used to be fairly common are rarer now and perceived to be colder than they would have been in the past. This is an example of adaptation, although not in a good way.
Andreas Schmittner
Professor, Oregon State University
1. The theory that global warming or Arctic warming slow the polar vortex, which makes it wavier and leads to more cold snaps in the US and other mid latitude regions is a theory with little evidence to support it. Cold snaps have always occurred and will continue to occur even as the globe is warming. This is part of natural climate variability.
2. There is ample evidence (see link above for an example) that global warming leads to fewer and less extreme cold snaps. So, the idea that global warming would make cold extremes more likely or worse is false.
3. Yes, climate scientists are confident that global warming makes winters warmer. There is ample evidence supporting this, not just temperature data, but also reducing snow cover and melting glaciers, increased pests such as the bark beetle and longer growing season. In fact, cold snaps become less likely and less severe due to global warming.
Yes, a wavier vortex leads to more cold and warm events. A strong zonal vortex has winds blowing west-to-east, but a weaker wavier vortex includes more north-to-south and south-to-north wind components. The region affected by the north-to-south wind receives cold air from the Arctic and experiences a cold event. Vice versa for the region affected by the south-to-north blowing wind, which gets warmer. In addition, a weaker and slower vortex leads to more persistent extreme events, often called blocking. That is when a weather system stays in place for longer than usual.
Jennifer Francis
Senior Scientist, Woodwell Climate Research Center
1. Yes, he’s basically correct, though the “polar vortex” he refers to is actually the jet stream. Our research has shown that when the Arctic is abnormally warm during winter, North America and Eurasia tend to be colder than normal. The true polar vortex is in the stratosphere and exists only in winter. When it becomes disrupted from it’s typically circular shape, it can intensify cold spells over the continents [see link here]
A winter cold spell is always caused by a large southward dip (aka trough) in the jet stream, as his graphics illustrate. These troughs occur naturally, but recent studies suggest jet stream waviness is increasing during winter, allowing cold spells to become more persistent and extend farther south. Disproportionate Arctic warming is one likely reason for this increased waviness, but other factors such as intensifying ocean heat waves and more frequent disruptions of the stratospheric polar vortex are also playing a role.
2. I would say that our recent review paper[5] provides convincing evidence for causal mechanisms contributing to this linkage. Natural variability is always large in winter, which makes it difficult to assess causes of any particular cold spell.
3. We’re confident that overall we’ll see fewer cold records broken. But it is also likely that regions ill equipped to deal with cold — such as Texas, New Orleans, the Middle East — will continue to suffer whenever Arctic air plunges southward in large jet-stream troughs.”
Additional question to Dr. Jennifer Francis:
SF: There seems to be some conflicting opinions among climate scientists about causality between arctic warming, polar vortex disruptions, and cold spells in mid-latitudes. (Even among the climate scientists who have responded to me thus far). Could you point out why the evidence in your recent paper offers more compelling evidence for causality? For example, does it offer new insights on some aspect of the theory that other climate scientists felt was missing or made them hesitant to accept the overall theory?
JF: “I wholly agree there is still much we don’t understand about connections between rapid Arctic warming and winter weather extremes (not only cold spells), but I think there are two fronts we addressed in this new paper that shed light on the topic. The first is a bit weedy, so I didn’t want to get into it too much, and that is the link between regional Arctic warming (strongest in areas of greatest sea-ice loss) and weakening of the north-south gradient in a quantity called potential vorticity, which is a measure of the tendency for moving air to take a curved path. When this quantity is smaller, there is a greater likelihood of blocking patterns to form in the jet stream. These blocks are like eddies in a river that become separated from the main flow and can swirl in one place for a long time. They have the effect of stopping weather systems from progressing, hence their name. The gradient in potential vorticity is smaller when the north-south temperature gradient is smaller, so as the Arctic warms rapidly, the conditions conducive to block formation are more likely. A favored location of blocks is near Greenland, which is associated with upstream troughs in the jet stream that create cold spells.
The second is evidence supporting the influence of rapid warming in the Barents/Kara Seas area (north of western Russia) on the stratospheric polar vortex. As this region warms faster than almost anywhere on Earth, it is sending wave energy upward that can “topple” the vortex, similar to poking a spinning top with your finger. If you poke it hard enough for long enough, eventually the spinning top will wobble. The same thing is happening to the vortex — it is more likely to become elongated or even split as this region warms. And we know when the vortex is disrupted, it tends to send its cold air southward where it can intensify cold-air outbreaks.
Zeke Hausfather
Climate Research Lead, Stripe
1. The idea that a rapidly warming Arctic is destabilizing the jet stream is an area of active scientific debate, with no clear consensus in the literature today. However, this effect is smaller than the rapid winter warming we’ve seen in recent years. The coldest days of the year have warmed rapidly, and the number of days below zero has decreased in every part of the United States.
2. As above, I think the jury is still out on the significance of the mechanism here, and recent research has made a pretty compelling case that there is a strong reduction in mid-latitude cold extremes even if there ends up being a demonstrable effect on atmospheric circulation.
3. We are confident broadly that both winters and the coldest days of the year are warming rapidly pretty much everywhere, and faster than annual average temperatures have been warming.
References
- 1 – IPCC (2021). Sixth Assessment Report.
- 2 – Blackport et al. (2024) Models and observations agree on fewer and milder midlatitude cold extremes even over recent decades of rapid Arctic warming. Science Advances.
- 3 – Rantanen et al. (2022) The Arctic has warmed nearly four times faster than the globe since 1979. Nature Communications Earth & Environment
- 4 – Cohen et al. (2021) Linking Arctic variability and change with extreme winter weather in the United States. Science.
- 5 – Hanna et al. (2024) Influence of high-latitude blocking and the northern stratospheric polar vortex on cold-air outbreaks under Arctic amplification of global warming. Environmental Research Climate.