Every once in a while, the polar vortex is coming to visit. It dips south over North America from its usual perch in the Arctic and brings freezing cold temperatures. While it might be hard to fathom when you are trying to avoid frostbite, researchers have found that more frequent mid-latitude visits by the polar vortex are likely a side effect of climate change.
Although those of us who live in locations like the United States and Europe rarely hear about it unless it’s heading our way, the polar vortex is around all year long. It’s an area of cold air with low atmospheric pressure over the Arctic. As with all areas with low pressure in the northern hemisphere, the winds of the polar vortex swirl counterclockwise and inward towards the North Pole. Around its outer fringes is the polar jet stream, a fast-flowing current of air that circles the Earth between the Arctic and the mid-latitudes.
Typically, a large difference in temperature between the air of the polar vortex and the air in the mid-latitudes drives the polar jet stream. However, the Arctic is warming faster than other areas of the planet, which makes the difference in temperature less distinct. This causes the polar jet stream to meander north and south instead of making a beeline around the planet. The meandering causes the cold air of the polar vortex to wobble, and, like a toupee that goes askew, it can slip south off of the Arctic over the United States, Europe, or Asia. As meteorologist Marshall Shepherd noted in Forbes, "Ironically and counterintuitive to many, the strong polar vortex can be linked, in part, to warmer temperatures."
Researchers have found that there is a connection between the polar vortex and Arctic sea ice. Each year Arctic sea ice waxes and wanes with the seasons, but over the past few decades there has been an overall loss of sea ice because of warming in the Arctic. Sea ice reached record low levels this year. (For example, take a look at the graph of November sea ice amounts below.) Scientists are still investigating the connection between the polar vortex and sea ice and the mechanism that causes ice to affect the vortex.
It’s possible that more frequent visits from the polar vortex may have dampened the effect of climate change in the mid-latitudes. Worldwide the climate is warming, but different regions of the world are seeing different affects. As the polar vortex occasionally brings colder than usual air to locations like Europe, Asia, and the United States, this can keep average temperatures from warming as much as other places on Earth.