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February 2021: Texas Freeze, Winter Storms, and the Polar Vortex

February 2021: Texas Freeze, Winter Storms, and the Polar Vortex

Record Low Temps in Texas.  In 2021, fluctuations to the polar vortex were responsible for the coldest February since 1989. According to the World Meteorological Organization (WMO), natural disruptions caused the polar vortex to weaken, wobble, and slip southward off the pole. The extreme weather event brought record-low temperatures to a large portion of central Canada, the United States and even northern Mexico. Temperatures recorded during February fell as much as 25 to 50°F below average.

Southern states in the U.S. were the most affected by the descending Arctic air, particularly in Texas and parts of Oklahoma and Arkansas. Other weather patterns interacted with the cold front to cause an unprecedented band of freezing air to linger over the South for most of early February.

Furthermore, severe winter storms during February brought heavy snowfall and treacherous icy conditions to large communities such as Houston, which rarely see snow at all. In Texas, the cold front caused further damage by putting significant strain on the municipal power grid and water supply. Millions of Texans lost power during the storm and were unable to heat their homes or prevent their water pipes from bursting. At least 217 people were killed directly or indirectly by the severe cold, and property damages were estimated to be at least $195 billion.

Making matters worse, the state’s power plants were not prepared to handle the sustained freezing conditions that are rare in Texas. The power grid failures led to further shortages in basic food supplies and clean drinking water as the winter storm interfered with supply chains and municipal plumbing grids. These shortages also made it harder for hospitals to care for thousands of patients suffering from hypothermia (subnormal body temperature) and other injuries caused by the storm. For those sticking it out at home, Texans were advised to boil their tap water to prevent risk of illness until wastewater treatment facilities could get back online.

Natural gas was hit the hardest of all the utilities in Texas because both the production and distribution pipelines froze and shut down. The problem only worsened as millions of freezing Texans turned up their heat. The abrupt spike in demand for natural gas for heating purposes led to shortages at power plants using natural gas to produce electricity. Some natural gas providers even took their power plants completely offline to avoid paying the high cost of fuel and to avoid long-term damage to their facilities. With coal, wind, and nuclear power plants also stressed with their own power shortages, the state’s energy grid collapsed in a time of great need. 

What is the polar vortex?  In recent years, “polar vortex” has become a commonly used term during winter weather reports throughout North America. While many people would recognize  this phrase or use it to describe colder than usual weather, its scientific meaning is complex and the natural phenomenon’s connection to climate change is still largely unknown.    

In essence, the polar vortex is a band of westerly winds that accumulates between 10 and 30 miles above the North Pole every winter (there is a similar polar vortex at the South Pole but it has less effect on weather in the Northern Hemisphere). Surrounding the vortex at lower altitude in the troposphere – 5 to 9 miles above the surface – the polar jet stream works to keep this large body of extremely cold air contained in the stratosphere.


Isolated from warmer latitudes by the polar jet stream below, the air inside the vortex grows progressively colder throughout the winter. During a normal winter when the polar vortex is stable, the polar jet stream is able to shift northward and more firmly contain the vortex of cold air (left diagram). In this scenario, the coldest polar air remains in the Arctic, resulting in milder weather in the mid-latitudes.

Conversely, in years when the polar vortex weakens or shifts, the polar jet stream can become wavier, lose strength, slow down, or sometimes reverse. These disruptions to the polar vortex’s usual position are called sudden stratospheric warmings because they allow warm air from the south to be pulled into the Arctic, which can contribute to glacial melt. When this happens, the displaced polar air is pushed south into the mid-latitudes, which can consequently cause the freezing temperatures and inclement winter weather the polar vortex is known for in America (right diagram). This phenomenon naturally occurs every few years but is hard to predict or prepare for.

Are severe winter storms caused by the polar vortex linked to climate change?  The extreme cold in the Southern Plains during February 2021 also coincided with warmer-than- average temperatures in the Arctic. It follows to wonder if changes in the frequency and severity of polar vortex fluctuation events is caused by or contributing to global warming. Are severe winter weather outbreaks in the mid-latitudes becoming more likely?

Because disruptions of the polar vortex occur when the polar jet stream below it is altered, any forces – including changes to surface and sea temperature that impact the strength or location of the polar jet stream – can act to initiate a release of cold air from the Arctic. It appears that warming in the Arctic and diminishing sea ice is causing the polar jet stream to meander irregularly in at least two places, which makes it more likely to disrupt the polar vortex. So it is plausible that even though there is an overall warming trend on Earth due to human-caused greenhouse gas emissions, we may see an increase in the severity of winter weather events in the mid-latitude regions of North America and Eurasia due to interactions of the warming with the polar vortex.

On the other hand, outbreaks of cold Arctic air are natural and have been a known part of our regular seasonal weather patterns in North America since the pattern was first recorded in the 1950’s. Sometimes the polar vortex can also be disrupted without significant impacts on surface weather in lower latitudes. For these reasons, blaming the polar vortex alone for colder winter weather in America might be seen as a bit of a stretch.

There are still many things climate scientists do not understand about the polar vortex, so it is hard to pinpoint climate change as the primary reason the polar vortex fluctuations are happening more regularly. Instead, scientists suggest the reason is likely more of a mix of random natural weather patterns and human-induced climate changes. While the polar vortex’s exact links to climate change are yet to be ascertained, colder-than-normal winter weather events are not likely to negate the long-term warming trend from climate change.

In fact, the WMO reports that overall cold temperature records are becoming rarer as heat records and heatwaves are becoming more common. This overall warming trend is anticipated to continue because worldwide greenhouse gas concentrations are on the rise. Even though February, 2021 was a particularly cold month in North America, globally the average carbon dioxide concentration in the same time period was 416.75 parts per million, up from 413.4 parts per million in February of 2020.

Why continuing to observe the polar vortex matters.  That the southern United States experienced a relatively cold winter this year should not be seen as proof that global warming isn’t happening. It is. We just don’t have a very long record of data on polar vortex fluctuations to know what patterns are normal (or random) and what patterns are being caused or intensified by climate change. Some climate models predict that continued warming and sea ice melt will lead to a weakening of the polar vortex. Other models predict the opposite. This discrepancy is largely because the correlation between Arctic surface and sea temperatures and the atmospheric systems above are intricate and have only been studied for several decades.

With the data available at present, the effect of global warming on the polar vortex appears to be small compared to the natural variability of the phenomenon. Any future influence the polar vortex may have on winter weather is predicted to be small compared to the overall warming influence of greenhouse gas emissions. On average, our winters in North America are still warmer than in the past, and record-setting cold extremes have become far less likely.

Even if extreme winter weather events caused by the Arctic polar vortex occur infrequently, their potential damage to communities in the southern United States and elsewhere around the world is significant and is worthy of further research and monitoring. The precise linkages between polar vortex fluctuations and climate change may still be unknown, but the more we can learn about this intricate relationship the better. Increasing our understanding of the polar vortex and how to predict its movements will extend the lead time both citizens and government officials have to prepare for the next big storm.


Associated Press. (2021, February 17). How ‘topsy turvy’ polar vortex brought record freeze to Texas. NBCNews.com. https://www.nbcnews.com/science/environment/topsy-turvy-polar-vortex-brought-record-freeze-texas-rcna290.

Bogel-Burroughs, N., & Nieto, G. M. (2021, February 20). Texas Winter Storm: What to Know. The New York Times. https://www.nytimes.com/2021/02/20/us/texas-winter-storm-explainer.html.

Lindsey, R. (2021, March 5). Understanding the Arctic polar vortex: NOAA Climate.gov. Understanding the Arctic polar vortex | NOAA Climate.gov. https://www.climate.gov/news-features/understanding-climate/understanding-arctic-polar-vortex.

UN News. (2021, March 9). Polar vortex responsible for Texas deep freeze, warm Arctic temperatures | | UN News. United Nations. https://news.un.org/en/story/2021/03/1086752.

Wikipedia. (2021, May 12). February 2021 North American cold wave. Wikipedia. https://en.wikipedia.org/wiki/February_2021_North_American_cold_wave.

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