Cold snaps, on average, are also becoming shorter. Winter in the lower 48 states warmed more than 4 1/2 times faster between 1970 and 2017 than it did over the past 100 years, according to the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center.
Confusion over winter storms on a warming planet usually comes down to misunderstanding weather versus climate.
One way to think about the difference is to remember that “climate is what you expect and weather is what you get,” said Adam Terando, a research ecologist with the United States Geological Survey.
While weather refers to short-term atmospheric conditions, climate considers the average weather of a specific region over a longer period.
The average amount of snow, for example, is declining in many parts of the country, while the amount of snow that falls during a snowstorm is increasing, according to the Environmental Defense Fund.
Along those lines, weather patterns since the 1950s show that the cold temperatures Chicagoans have been experiencing this week used to be much more common, Terando said.
“Overall, we’re still driving the Earth’s climate to a warmer place over time … but around the averages, you can still have cold weather extremes like we’re experiencing now,” he said.
Imagine walking a dog. Although you’re instructing the dog where to walk and it may be staying on the path, the animal will still wobble or sway from one side of the sidewalk to the other, Terando explained.
“Those are the day-to-day fluctuations in the weather that we talked about,” he said.
The polar vortex — strong winds in the Arctic Circle that trap cold air above the North Pole — could also play a role. If that vortex weakens, cold air can move south.
El Nino events in the fall and winter can also cause wetter-than-average conditions from Southern California to along the Gulf Coast and drier-than-average conditions in the Pacific Northwest and Ohio Valley, according to the NOAA. El Nino winters increase the likelihood of warmer-than-average temperatures across the northern part of the U.S.
“Overall, we’re adding greenhouse gases to the atmosphere,” Terando said. “That causes less warmth and heat to escape out to space, and that means the planet will get warmer. That’s what we’re experiencing.”