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© Getty Images
0 / 31 Fotos
January 2025
- The first half of January 2025 brought severe wintry weather to certain parts of the US.
© Getty Images
1 / 31 Fotos
Early storm
- To kick things off, a storm at the beginning of the month caused seven states to declare a state of emergency.
© Getty Images
2 / 31 Fotos
Disruption
- Flights were canceled, businesses shut down, and in one area of New York, there was a huge dumping of snow—6.25ft (1.9m) in just 24 hours.
© Getty Images
3 / 31 Fotos
Lower than average temperatures
- Into the middle of January, another wave of Arctic air kept temperatures lower than would generally be expected for the time of year.
© Getty Images
4 / 31 Fotos
The cause
- According to experts, this blast of cold weather is due to a weakening in the polar vortex, otherwise known as the Arctic polar vortex.
© Shutterstock
5 / 31 Fotos
What is the polar vortex?
- The polar vortex is a ring of strong westerly winds that form between 10 and 30 miles (16-48 km) above the North Pole each winter.
© Shutterstock
6 / 31 Fotos
How it works
- These winds enclose a pool of extremely cold air. The stronger the winds, the better the freezing air is isolated from warmer areas.
© Shutterstock
7 / 31 Fotos
When stable
- When the vortex is stable, i.e. when the winds are strong, the polar jet stream shifts northward, which helps to keep the coldest air in the Arctic.
© Shutterstock
8 / 31 Fotos
When unstable
- However, when the vortex becomes unstable, this can allow the extremely cold air to escape further south.
© Shutterstock
9 / 31 Fotos
Impact on the US
- In certain cases, this can cause a cold snap to occur at mid-latitudes, where the US sits.
© Getty Images
10 / 31 Fotos
Extreme effects
- Although the polar vortex does not always influence weather in the US, when it does, the effects tend to be very extreme.
© Getty Images
11 / 31 Fotos
Expert opinion
- Meteorologist Brett Anderson has described the cold outbreak in January 2025 as “basically broken off pieces of the polar vortex.”
© Getty Images
12 / 31 Fotos
The impact of climate change
- In terms of whether climate change will affect the polar vortex, the jury is still out. This is because there are multiple factors to consider.
© Shutterstock
13 / 31 Fotos
Melting ice
- On the one hand, there are models that suggest melting sea ice may serve to weaken it.
© Getty Images
14 / 31 Fotos
Warming atmosphere
- On the other hand, there are also studies that suggest warming in the upper layers of the atmosphere could serve to strengthen the polar vortex.
© Shutterstock
15 / 31 Fotos
Sea surface temperatures
- Experts also believe that regional changes in sea surface temperatures could also have a role to play.
© Shutterstock
16 / 31 Fotos
No consensus
- According to atmospheric scientist Amy Butler, the models show “no agreement in what will happen to the Northern Hemisphere polar vortex in the future.”
© Shutterstock
17 / 31 Fotos
Climate change and winter weather
- In fact, scientists are uncertain in general about how climate change will affect extreme winter weather.
© Shutterstock
18 / 31 Fotos
Decrease in snowfall
- What we do know is that in many parts of the US, total snowfall has decreased since we began making records in the 1930s.
© Getty Images
19 / 31 Fotos
Snow falling as rain
- One of the reasons for this decline in snowfall is the warmer air temperatures. This causes winter precipitation to fall as rain instead of snow.
© Shutterstock
20 / 31 Fotos
Statistics
- Indeed, between 1949 and 2024, more than 80% of the weather stations across the 48 contiguous states measured a decrease in the proportion of precipitation falling as snow versus rain.
© Shutterstock
21 / 31 Fotos
General trend
- In general, then, cold snaps in North America have become less frequent and less extreme over the course of the last century.
© Getty Images
22 / 31 Fotos
Caveat
- However, when they do occur, cold snaps are often more dangerous than they used to be because communities are no longer prepared for them.
© Getty Images
23 / 31 Fotos
More intense
- There are also cases of winter storms being more intense than they would have been in the past due to the warmer atmosphere.
© Getty Images
24 / 31 Fotos
Moisture in the air
- A warmer atmosphere means more moisture in the air, and more moisture means more potential snow.
© Getty Images
25 / 31 Fotos
Conditions for snow
- Indeed, in order for it to snow, two basic conditions must be met: the air temperature must be below freezing, and there must be moisture in the atmosphere.
© Getty Images
26 / 31 Fotos
Actual trend
- However, what we’re actually seeing in many places is a trend towards more winter rain and/or mix events (winter weather that involves different types of precipitation).
© Getty Images
27 / 31 Fotos
Expert analysis
- According to Anderson, as the planet continues to warm, there will be more energy and moisture available for bigger winter storms.
© Getty Images
28 / 31 Fotos
Long-term trend
- There is a clear long-term global trend for snow: cold extremes will become less frequent and less extreme with climate change.
© Getty Images
29 / 31 Fotos
Lots of variation
- However, there will likely be considerable local variation, and winter storms will continue to present a challenge even as the planet warms. Sources: (BBC) See also: Can refreezing polar regions mitigate global warming?
© Getty Images
30 / 31 Fotos
© Getty Images
0 / 31 Fotos
January 2025
- The first half of January 2025 brought severe wintry weather to certain parts of the US.
© Getty Images
1 / 31 Fotos
Early storm
- To kick things off, a storm at the beginning of the month caused seven states to declare a state of emergency.
© Getty Images
2 / 31 Fotos
Disruption
- Flights were canceled, businesses shut down, and in one area of New York, there was a huge dumping of snow—6.25ft (1.9m) in just 24 hours.
© Getty Images
3 / 31 Fotos
Lower than average temperatures
- Into the middle of January, another wave of Arctic air kept temperatures lower than would generally be expected for the time of year.
© Getty Images
4 / 31 Fotos
The cause
- According to experts, this blast of cold weather is due to a weakening in the polar vortex, otherwise known as the Arctic polar vortex.
© Shutterstock
5 / 31 Fotos
What is the polar vortex?
- The polar vortex is a ring of strong westerly winds that form between 10 and 30 miles (16-48 km) above the North Pole each winter.
© Shutterstock
6 / 31 Fotos
How it works
- These winds enclose a pool of extremely cold air. The stronger the winds, the better the freezing air is isolated from warmer areas.
© Shutterstock
7 / 31 Fotos
When stable
- When the vortex is stable, i.e. when the winds are strong, the polar jet stream shifts northward, which helps to keep the coldest air in the Arctic.
© Shutterstock
8 / 31 Fotos
When unstable
- However, when the vortex becomes unstable, this can allow the extremely cold air to escape further south.
© Shutterstock
9 / 31 Fotos
Impact on the US
- In certain cases, this can cause a cold snap to occur at mid-latitudes, where the US sits.
© Getty Images
10 / 31 Fotos
Extreme effects
- Although the polar vortex does not always influence weather in the US, when it does, the effects tend to be very extreme.
© Getty Images
11 / 31 Fotos
Expert opinion
- Meteorologist Brett Anderson has described the cold outbreak in January 2025 as “basically broken off pieces of the polar vortex.”
© Getty Images
12 / 31 Fotos
The impact of climate change
- In terms of whether climate change will affect the polar vortex, the jury is still out. This is because there are multiple factors to consider.
© Shutterstock
13 / 31 Fotos
Melting ice
- On the one hand, there are models that suggest melting sea ice may serve to weaken it.
© Getty Images
14 / 31 Fotos
Warming atmosphere
- On the other hand, there are also studies that suggest warming in the upper layers of the atmosphere could serve to strengthen the polar vortex.
© Shutterstock
15 / 31 Fotos
Sea surface temperatures
- Experts also believe that regional changes in sea surface temperatures could also have a role to play.
© Shutterstock
16 / 31 Fotos
No consensus
- According to atmospheric scientist Amy Butler, the models show “no agreement in what will happen to the Northern Hemisphere polar vortex in the future.”
© Shutterstock
17 / 31 Fotos
Climate change and winter weather
- In fact, scientists are uncertain in general about how climate change will affect extreme winter weather.
© Shutterstock
18 / 31 Fotos
Decrease in snowfall
- What we do know is that in many parts of the US, total snowfall has decreased since we began making records in the 1930s.
© Getty Images
19 / 31 Fotos
Snow falling as rain
- One of the reasons for this decline in snowfall is the warmer air temperatures. This causes winter precipitation to fall as rain instead of snow.
© Shutterstock
20 / 31 Fotos
Statistics
- Indeed, between 1949 and 2024, more than 80% of the weather stations across the 48 contiguous states measured a decrease in the proportion of precipitation falling as snow versus rain.
© Shutterstock
21 / 31 Fotos
General trend
- In general, then, cold snaps in North America have become less frequent and less extreme over the course of the last century.
© Getty Images
22 / 31 Fotos
Caveat
- However, when they do occur, cold snaps are often more dangerous than they used to be because communities are no longer prepared for them.
© Getty Images
23 / 31 Fotos
More intense
- There are also cases of winter storms being more intense than they would have been in the past due to the warmer atmosphere.
© Getty Images
24 / 31 Fotos
Moisture in the air
- A warmer atmosphere means more moisture in the air, and more moisture means more potential snow.
© Getty Images
25 / 31 Fotos
Conditions for snow
- Indeed, in order for it to snow, two basic conditions must be met: the air temperature must be below freezing, and there must be moisture in the atmosphere.
© Getty Images
26 / 31 Fotos
Actual trend
- However, what we’re actually seeing in many places is a trend towards more winter rain and/or mix events (winter weather that involves different types of precipitation).
© Getty Images
27 / 31 Fotos
Expert analysis
- According to Anderson, as the planet continues to warm, there will be more energy and moisture available for bigger winter storms.
© Getty Images
28 / 31 Fotos
Long-term trend
- There is a clear long-term global trend for snow: cold extremes will become less frequent and less extreme with climate change.
© Getty Images
29 / 31 Fotos
Lots of variation
- However, there will likely be considerable local variation, and winter storms will continue to present a challenge even as the planet warms. Sources: (BBC) See also: Can refreezing polar regions mitigate global warming?
© Getty Images
30 / 31 Fotos
How the polar vortex causes intense wintry weather
The main culprit of the January 2025 storms
© Getty Images
In January 2025, the winter weather in the US has been a lot more extreme than expected. Everyone is quick to blame climate change, but according to experts, there is something more specific at play.
The polar vortex, which is a band of strong winds that encloses a pool of freezing cold air in the Arctic, can cause extreme wintry weather in the US when it becomes unstable.
Curious? Check out this gallery to find out more.
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