Chicago natives are no stranger to arctic weather, suffering through subzero temperatures at least once a year. But this winter, temperatures are plummeting to near negative 55 degrees Fahrenheit with wind chill, making Chicago colder than even the South Pole. And the reason may be surprising: global warming.
Global warming is a hot button topic, but there’s no denying that the earth has changed in the last century. According to the National Aeronautics and Space Administration (NASA), the planet’s temperature has risen by 1.62 degrees Fahrenheit since the late 19th century, with most of the change happening in the last 35 years. This has many repercussions, including the melting of polar ice. Between 1993 and 2016, the Greenland ice sheet lost 281 billion tons of ice per year, and Antarctica lost 119 billion tons of ice per year. This melting has caused sea levels to rise by eight inches, with the rate increasing every year.
The most affected places have been at the poles, with the Arctic warming at twice the rate of the global average. Ice is very reflective, so not a lot of sunlight is absorbed, and the heat is bounced back out into space. Water, however, is good at trapping heat, so when the temperature rises, ice melts, the water traps heat, the temperatures rise even further and even more ice melts in a feedback loop termed polar amplification.
Jennifer Francis, a senior scientist at the Woods Hole Research Center, explained this phenomenon in an interview with The New York Times.
“When we lose a lot of ice in that particular area in the summer, it absorbs a lot of extra heat from the sun,” Francis said. “And so we see a very persistent, hot spot there in terms of temperature differences from what they should be.”
The raising temperatures and sea levels aren’t just killing polar bears or drowning cities — it’s also blasting frigid air into mid-latitude cities, like Chicago. This is because of a break down of the polar vortex.
Now a common phrase, the polar vortex is not just a coined name for a cold spell. AccuWeather Chief Video Meteorologist Bernie Rayno explained this in an interview.
“The polar vortex is not a recently discovered phenomenon; in fact, it has been talked about in the meteorological world for decades,” Rayno said.
The polar vortex is actually a jet stream of wind that circles high in the atmosphere above the Arctic. It is caused by the difference in temperature between the pole and mid-latitudes, which also causes a pressure difference. Air always flows from high pressure to low pressure in an attempt to equalize the pressure, creating wind. The spin of the earth causes the wind to travel in a circle around the Arctic, a process called the Coriolis effect.
Usually this jet stream is very fast, keeping all the cold, Arctic air contained above the pole. However, unusually warm temperatures reduce the pressure difference between the pole and mid-latitudes, causing the polar vortex to slow down. This allows the pocket of cold air above the Arctic to slip out into Canada and the northern U.S., causing a short period of frigidly cold days.
The breakdown of the polar vortex every now and then is natural. Historical polar vortex’s occurred in 1977, 1982, 1985, 1989 and 2014, which launched the term polar vortex into every day vocabulary. But none of those were as powerful as the one the U.S. is currently experiencing. Although global warming is causing shorter winters, the effect on the polar vortex is making those short winters much more intense.
Thankfully, Baltimore seems to be right at the edges of the polar vortex’s reach, but the earth is hardly predictable — it would be smart to make sure your naive California friends are well prepared.