If it's getting warmer, why is it so cold?

The Midwest was again caught in the icy grip of the “polar vortex” this winter, resulting in record-low temperatures that nearly rivaled the frigid temperatures in the beginning of Jan. 2014. For many in the Midwest, the bitter cold during these recent polar vortex winters has been frozen into memory.

The same is true for trees.

New research led by Steve Voelker, a dendroclimatologist from Utah State University, could help scientists understand the history of these chilling events.

Voelker said the research, published in the journal Scientific Reports on March 12, demonstrates for the first time, “how scientists can reconstruct winter temperatures from hundreds of years ago with tree rings.”

It also “has connections to both local and larger-scale climate issues,” he said.

Climate leaves signatures on every living thing, but some trees and conditions retain these better than others.

These memories of past climate are stored in the size and composition of tree growth rings. Voelker specializes in researching the chemical composition of these rings, which contain signatures of historical conditions.

Voelker and his team have found the atoms that make up growth rings in trees around Lake Superior have characteristics strongly linked to climate patterns, ice coverage of the lake, and winter temperatures in the region.

The connection of these variables to past climates also allows scientists to make more accurate predictions for the future. Specifically, Voelker is interested in the information contained in trees to learn more about events like the polar vortex. This climate phenomenon has gained media traction in the past 10 years because it is associated with record-breaking low temperatures that turn into billion-dollar disasters for business and industry in the Midwest and Northeast regions of the country.

“We hope to reconstruct winter polar vortex activity back in time and understand if the huge swings we’ve seen recently are anomalous or not and if they are related to global warming,” Voelker said. Climate change is projected to increase the variability of climate patterns and events, resulting in more extreme and energetic weather. Voelker said this enhanced variability will cause issues that are hard to foresee.

“If you’re worried about clearing your roads of snow and you’re under a warmer climate, you’re not going to employ as many drivers on a regular basis or have as many trucks,” Voelker said. “Then again, you may need these resources more suddenly due to amplified variability. That variability has a cost in and of itself.”

The implications are far-reaching. Voelker referenced the impact of ice buildup during polar vortex years on the Great Lakes and its impact on shipping, the cost of heating and energy production during deep-freeze events and travel delays due to extreme storms.

“There is a cost, and it’s not as obvious as some people might see,” Voelker said.

While it might seem counterintuitive to imagine a warmer world with more severe winter weather, the unique climate of North America could be making this possible. Simon Wang, a coauthor of the article and climatologist at USU, studies how events like the polar vortex are linked to severe drought in the West.

Wang’s research has connected the severe California drought of 2014 and the recent polar vortex events to an atmospheric circulation pattern known as the “dipole.” This pattern of rising and falling air over North America connects conditions affecting dry weather and drought in the West with the frigid cold events occurring in the Northeast.

“This new research will help us understand whether or not the recent increase in cold winters over the eastern U.S. is traced to global warming,” Wang said.

As climate change is also expected to amplify or exacerbate the dipole, the United States is facing a unique situation in which more dramatic winter climate variability could have drastically different impacts in different regions of the country.

The connected nature of these extreme events in the western and eastern United States makes Voelker and Wang’s research important to climate adaptation for the nation. Even though the trees used in this study are a continent away, “they have the potential to improve our knowledge of past drivers of drought and flooding in California,” Voelker said. “That’s what’s important for Utah and the west.”