Around this time last year, Texas experienced an intense and damaging Arctic blast of cold air. Texas, of all places! This week, the “polar vortex” is at it again, bringing snow, ice and incredibly cold temperatures, this time across the central and eastern US. So, what’s going on? How can Arctic air reach so far south?

It has to do with a counter-clockwise spinning mass of cold air that hovers above the Arctic called the “polar vortex”, which grows and shrinks with the changing seasons. When stable, it remains closer to the North Pole, constrained by a strong polar jet stream. When there is a large temperature difference between the warmer mid-latitudes and the polar region, the jet stream is strong and keeps the polar vortex stable. But when the difference is smaller, the jet stream weakens and gets more wavy. This can cause the polar vortex to “break off” and plunge towards the south, bringing cold Arctic air with it.

Is climate change to blame? In a nutshell, yes. In particular, the loss of sea ice due to warming temperatures has led the highly reflective surface of ice to transform to a dark absorbing surface of water instead. This change is warming the higher latitudes and reducing the temperature difference between the mid-latitude and polar regions. That, in turn, weakens and destabilizes the polar jet stream. Future climate change likely will further weaken the polar jet stream, bringing rise to more extreme and unusual weather patterns. Global warming. Climate change. These terms have helped us define, through time, the changes that we’re witnessing. Perhaps a more accurate descriptor now is “climate destabilization.”

photo: Ulyana Horodyskyj, in Colorado