In mid-January 2024, extreme Arctic air and severe weather moved southward across the U.S., breaking low-temperature records in states from Montana to Texas. Dangerously low temperatures affected tens of millions, while heavy lake-effect and snow squalls ravaged the Northeast and Great Lakes regions.
The Polar Jet Stream, the jet stream that separates the Arctic from the more temperate air, dips deep southward, bringing cold Arctic air into regions that are not used to it.
Surface temperatures as of 7 a.m. on January 16, 2024. Temperatures are shown in blue for temperatures below freezing and red for those above freezing. The light blue line is arrowed. Mathew Barlow/UMass Lowell, CC BY
A fascinating aspect of these events are that they occur often in conjunction with changes in another river of high-altitude air, the stratospheric vortex. This is a large stream of air that moves around the North Pole in the middle of the stratosphere.
This stratospheric whirlwind can also distort and stretch the jet stream, causing it to move southwards in certain areas.
The Arctic polar vortex (also known as the Arctic vortex) is a powerful band of wind in the stratosphere. It can be found 10-30 miles above ground. This band of wind, which normally circles the North Pole and is a strong one, can break when it weakens. Polar jet streams can reflect this instability, becoming weaker and more wavy. Cold air is forced southward at some locations. NOAA
This pattern was followed by the Arctic cold blast of January 2024, when the polar vortex had stretched so far across the U.S. that it nearly split in half. A number of factors could have caused this stretching, but the most likely one is high latitude weather over the previous two weeks.
Surface temperatures and jet stream at 7 am EST, January 16, 2024. The stratospheric vortex is also shown in dark blue. Mathew Barlow/UMass Lowell, CC BY
A polarized view of the wind in the lower stratosphere, at 7 am EST, on January 16, 2024. The lower stratosphere winds are shown at approximately 10 miles. Mathew Barlow/UMass Lowell
Cold doesn’t contradict climate change.
It may be surprising that Earth has set so many records for Cold after just experiencing its hottest record year. Does this recent cold snap contradict global warming caused by humans? Climate and atmospheric scientist, it absolutely does not.
A single weather event cannot prove or disprove the existence of global warming. Numerous studies have demonstrated that global warming is causing a decrease in extreme cold events.
The open question is whether global warming, contrary to expectations, may play a supporting role in these events’ intensity. Some research indicates that it is.
The February 2021 Cold Wave that seriously disrupted Texas’s electric grid was also related to a stretched stratospheric vortex. We have presented evidence that suggests Arctic changes linked to global warming increased the likelihood of vortex disruptions. The improved high-latitude heating, known as Arctic Amplification, may have an impact on regional sea ice and snow cover, which could lead to a stretched polar whirlwind.
We have recently shown that, for large parts of the U.S. and Europe, as well as Northeast Asia, the number of severe cold events has clearly decreased – which is expected due to global warming. However, it appears that the intensity of those events has not reduced correspondingly, despite rapid warming of their Arctic origin regions.