Polar Vortex Reverses Direction in Earliest Disruption on Record, Raising Winter Cold-Snap Risk

Roughly 10 to 50 kilometers above the Arctic, a ring of cold, low-pressure air normally spins counterclockwise around the North Pole. This year, observations show its winds have turned the other way. Scientists say the reversal is the earliest disruption of the polar vortex ever recorded.

Tim Stockdale and Frederic Vitart, principal scientists at the European Centre for Medium-Range Weather Forecasts, told the AFP news agency that, as far as they know, it is the earliest stratospheric vortex disruption ever observed. Meteo-France, the French weather agency, called it an unprecedented event. What the disruption will do to the Northern Hemisphere winter is not yet clear, but researchers agree the record itself is not in doubt.

The vortex sits just above the jet stream, another band of powerful winds, which marks the boundary where cold Arctic air meets warmer air from the tropics and subtropics. In some winters the vortex stays a tight circle that holds the coldest air near the pole. In others it forms uneven waves that dip south. As its strength and shape change, it can shift the jet stream below, and the jet stream is what steers weather on the ground. A wavier jet stream that plunges south can let freezing Arctic air spill toward lower latitudes.

One of the biggest triggers of this kind of upheaval is sudden stratospheric warming, in which temperatures in the polar stratosphere climb sharply within a few days and the vortex's strong westerly winds weaken. The vortex can then be knocked off the pole, split into several rings, or, as now, see its westerlies change direction. Recovery can take several weeks.

The consequences can be severe. An earlier disruption contributed to the Great Texas Freeze of February 2021, which brought more than a week of freezing temperatures, power outages, and the deaths of hundreds of people. Judah Cohen, a climatologist at the Massachusetts Institute of Technology, told AFP that this early breakdown raises the chance of cold air outbreaks in the latitudes where most of the Northern Hemisphere's densely populated centers lie: the United States, Europe and East Asia.

But severe cold is not guaranteed. The UK's Met Office stresses that the vortex can tilt the odds toward cold, but it is not a switch that turns cold weather on and off. Other weather patterns also shape the outcome.

One is El Nino, the warming of surface waters in the central and eastern equatorial Pacific, which is associated with milder winters. The current event is intensifying, is expected to peak at the end of the year, and has been classified as exceptionally strong, disrupting weather around the globe. Cohen said El Nino could moderate or modify the vortex's effects, though he added that this was not certain.

There is also a longer-term question. Some research ties the rapid warming of the Arctic, driven by climate change, to more frequent vortex disruptions, which would mean some regions could still see harsher cold spells even as the planet warms. That link is not conclusive and remains debated among scientists.

The thing to watch in the coming weeks is how the vortex's slow recovery plays out against a strengthening El Nino, and whether cold air actually reaches the populated regions Cohen named.