If Earth is Warming, Why Is It So Cold?

Born and raised in Chicago, I know cold and windy. But nothing like this week’s bitterly cold Arctic air blast. Temperatures plummeted to 23 degrees below zero, -50 with the wind chill. Lake Michigan smoked and churned like witches’ brew in a boiling cauldron. Ice floats covered the Chicago River. According to FlightAware, 2,600 flights were cancelled throughout the US, more than 1,400 of them at Chicago’s O’Hare International Airport.

These periods of extreme cold cause some to ask “If Earth is warming, why is it so cold?” The answer requires an understanding of the difference between weather and climate. Weather is short term. Today, tomorrow, this week. Climate is the long view. Climate can be thought of as the sum of weather over a long period of time and it is getting more extreme.

So what is causing the horrendous weather across the country’s mid section this week? The Polar Vortex. It is a system of wind and cold air usually contained over the North Pole but which broke apart this month depositing its dangerously cold temperatures in different places. The New York Times visually demonstrates the phenomenon in an animated 3D, but I will summarize.

The Polar Vortex comes to life in winter, 10 miles above the ground. Like a cyclone, the vortex is a spinning wall of powerful winds surrounding a single center. When those powerful winds weaken, it causes the vortex to shift or even break into pieces. This January, the vortex split into parts. Instead of a single vortex, the swirling parts spread across the Earth. In so doing, the typical jet stream pattern warped, forcing freezing Arctic air further south and allowing warm air to flow further north.

Think of the jet stream as a wall, separating the warm air below it from the cold air above it. But instead of a straight wall circumnavigating the Earth around the North Pole, the wall is wave shaped, higher in some spots, lower in others. Warm air floating north stops at the wall’s most northern point. Similarly, Arctic air moves freely south until it bumps into the southern most tip of the wall.

This week, the jet stream’s southern most tip dipped south of the Great Lakes allowing Arctic air to freely descend down to the middle of the country, freezing everything it touched.

How is this related to climate change? Scientists say that melting polar ice in summer absorbs more heat, causing ocean hot spots. Come mid to late winter, those hot spots along with the jet stream driven by climate change causes the polar vortex to break down. As the Arctic warms, more severe weather is anticipated. While colder temperatures appear to be arriving later, when it does arrive, it is often very intense. Hence, extreme weather. WINTER IS HERE.

Here is the New York Times’ animated 3D view of the jet stream and polar vortex.
https://www.nytimes.com/intera...