Studying historical hourly weather data – and the amount of time that temperatures remain above or below certain thresholds – reveals several impacts of U.S. regional climate change trends. In a new study, researchers from North Carolina State University found that over the past four and a half decades, areas in the northeastern U.S. have lost almost 1 1/2 weeks of temperatures below freezing, while portions of some states in the Gulf and Southwest have gained almost 1 1/2 weeks of temperatures that cause heat stress. The data can be used to inform climate adaptation planning.

“One of the challenges when talking about and planning for climate change is that the average change seems too small to be significant,” says Sandra Yuter, Distinguished Professor of Marine, Earth and Atmospheric Sciences at NC State and corresponding author of the study. “Two or three degrees doesn’t make much difference if your average daily temperature is 65 degrees Fahrenheit. But it can make a huge difference if your typical temperature was 30 F and that increases to 33 F.”

The research team looked at hourly weather station data obtained from the National Centers for Environmental Information’s Integrated Surface Database Lite – which contains data from 340 weather stations in the contiguous U.S. and southern Canada – from 1978 to 2023. For each station, they computed decadal trends in hours below the freezing point (0 degrees Celsius, 32 F) and hours above the threshold for heat stress in animals and plants (30 C, 86 F).

“The length of time that temperatures exceed thresholds like the one for heat stress is important,” Yuter says. “Maximum temperatures of 90 F (32 C) recorded for six hours over the course of a day will have substantially different impacts on people, animals, plants and buildings compared to the same maximum temperature recorded for only one hour of a day.”

Overall, they found that the most dramatic impacts were in the northeastern U.S. during winter. Many weather stations east of the Mississippi River and north of the 37th parallel have lost the equivalent of about 1 1/2 to 2 weeks of temperatures below 32 F (0 C).

They also found that locations in Arizona, New Mexico, and parts of southern Nevada, southern California and southern Texas have gained the equivalent of about 1 1/2 weeks of temperatures higher than 86 F (30 C), a threshold at which agricultural crops and animals start to experience heat stress symptoms.

Some areas, such as the Midwest, showed no significant trends due to the high variability of temperatures from year to year.

The researchers hope that the data can help policymakers, businesses, and homeowners justify and plan climate adaptations.

“Our main aim with this analysis is to explain how climate change is occurring in a manner that aligns with lived experiences so that people can understand it and take pragmatic action to adapt,” Yuter says. “The U.S. is a big country, so changes will look different depending on your region, but the work demonstrates that hourly temperature data is potentially useful in determining where there will be effects on ecological patterns and organism behaviors, energy usage, and growing season duration across the country.”

The work appears in PLOS Climate and was supported by the NC State University Provost Professional Experience Program, the National Aeronautics and Space Administration (80NSSC19K0354), the Office of Naval Research (N00014-21-1-2116 and N00014-24-1-2216), and the Robinson Brown Ground Climate Study donation fund. Former NC State undergraduate student Logan McLaurin is first author. Other NC State contributors include former Ph.D. student Kevin Burris and Senior Research Scholar Matthew Miller.

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