Climate Matters•January 25, 2023
Fewer Frigid Nights
KEY CONCEPTS
204 U.S. locations have seen a drop in the annual number of freezing nights since 1970.
The average change across these 204 locations was 13 fewer freezing nights.
Local trends since 1970 are part of a larger trend: the most rapid warming in the U.S. has generally occurred when it’s typically coldest—including at night and during winter.
These trends are likely to continue with additional heat-trapping emissions. By the middle of this century, 23 states are projected to see at least three or four fewer weeks of freezing days.
Fewer freezing days and nights may reduce cold weather hazards and heating costs, while also negatively impacting economies and ecosystems that depend on the cold.
The coldest time of year
The coldest nights of the year are upon us, bringing serious risks. When thermometers drop to their annual minimums, cold weather hazards and home heating costs both spike and many struggle to stay warm.
The coldest time of year also plays important roles in plant, animal, and insect life cycles, recharging snowpack that supplies freshwater, and sustaining snow and ice for winter recreation and associated local economies.
For most of the U.S., the coldest nights of the year are warming.
Fewer frigid nights
Climate Central analyzed local trends in the number of coldest nights each year from 1970 to 2022. What is considered a cold night differs from Minneapolis to Miami. Locations were therefore assigned different low temperature thresholds based on their climatology (see methodology for details).
Of the 247 U.S. locations analyzed, 231 had at least one day at or below freezing in at least half the years in the period of analysis.
Of these 231 locations, 204 (88%) have experienced a long-term decrease in the annual number of freezing nights since 1970.
Of the 204 that have experienced a decrease in freezing nights, the average decrease since 1970 was 13 fewer nights below freezing.
The locations that have experienced the largest decreases in the number of nights at or below 32°F were: Reno, Nev. (91 fewer freezing nights); Albuquerque, N.M. (45 fewer freezing nights); and Bend, Ore. (41 fewer freezing nights).
Some locations that previously experienced freezing nights during earlier decades now no longer do—including Las Vegas, Nev.; New Orleans, La.; Phoenix, Ariz.; and several locations in California (San Francisco, San Jose, and Santa Maria) and Florida (Fort Myers, Sarasota, Tampa Area, and West Palm Beach).
Cool places and seasons warm quickly
The observed trends since 1970 are part of a longer-term trend.
The most rapid warming in the U.S. has generally occurred when and where it’s usually the coldest, including at night, in northern parts of the country—and during winter.
Winter was the fastest-warming season for 74% of 246 U.S. locations analyzed by Climate Central.
Nationwide, the rate of warming for nighttime lows since 1900 (1.78°F per century) is about 25% faster than the rate of warming for daytime highs (1.42°F per century).
Fewer future freezes
Climate models suggest that the coldest times of the year will continue to warm if emissions of heat-trapping greenhouse gases continue.
The Climate Impact Lab modeled future scenarios of the change in annual days below freezing.
Under a medium-high emissions scenario, every state in the contiguous U.S. (and Alaska) will experience a drop in days with below-freezing temperatures by 2040.
By the middle of the century, 23 states—especially in the Northwest, Southwest, Plains, Upper Midwest, and Northeast—are projected to see at least three or four fewer weeks of freezing days.
Fewer freezes: cold weather hazards
Extreme cold comes with serious risks. During the December 2022 winter storm, more than two-thirds of the U.S. population (those under weather advisories or warnings) experienced these risks. The storm and Arctic front sent temperatures plummeting across the central and eastern U.S., left more than one million people without power, and contributed to an estimated 87 fatalities.
A long-term decrease in the number of freezing days and nights may reduce some of the most acute risks of cold exposure among vulnerable populations, including the hundreds of thousands of people experiencing homelessness in the U.S. Hazardous extreme cold events such as the December 2022 winter storm still occur in a warming climate, however.
As the coldest nights of the year warm, the costs of home heating may also decrease, reducing the economic burden on many families. The total U.S. winter heating degree days have decreased since 1974, along with residential winter natural gas usage.
Fewer freezes: cold weather benefits
Although fewer freezing days and nights can reduce the risks and costs associated with the coldest times of year, these trends can also have negative consequences for economies and ecosystems that depend on the cold.
Warming during the coldest time of year can disrupt snowfall patterns, which can in turn limit snow-fed water supplies that people, agriculture, and ecosystems rely on throughout the year.
Communities and businesses reliant on winter recreation may find it difficult to maintain snow and ice. That means less ice for ice fishing, fewer cross-country ski days, and shorter snowboarding seasons.
A lack of cold can prolong the active season and expand the range for disease-carrying pests such as ticks and mosquitoes. According to the EPA, the increasing number of cases and the growing distribution of Lyme disease are indicators of climate change.
Yields of high-value fruit crops that require a minimum number of winter chill hours can also be impacted by a decrease in the number of freezing days and nights.
LOCAL STORY ANGLES
What are the local impacts of extreme cold nights in your state or region?
Climate Central’s report On Thin Ice covers the impacts of warming winters on America’s cold-weather sports economy and the communities that depend on it. According to Climate Central’s Surging Power Outages and Climate Change analysis and report, 22% of the 1,542 weather-related power outages from 2000–2021 were caused by winter weather. The EPA Indicator, Cold-Related Deaths, reviews trends and contributing factors in mortality due to cold temperature extremes.
Who is most at risk from extreme cold nights in your local area?
Older adults, children, sick individuals, people experiencing homelessness, and pets all face greater risks from extreme winter weather. Low-income individuals facing higher home heating costs are also at risk when overnight temperatures drop, and may qualify for home energy assistance programs. Ready.gov provides guidance to prepare and stay safe, and your city or county may have a cold weather emergency plan. Criteria for winter storm watches, advisories, and warnings can vary by region so check out your local National Weather Service office.
CONTACT EXPERTS
Kyri Baker, PhD
Assistant Professor
University of Colorado Boulder
Relevant expertise: Power systems, grid resilience to freezes
Contact: Kyri.Baker@colorado.edu
FIND EXPERTS
Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts.
Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.
Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs and Diverse Sources to find and amplify diverse expert voices.
Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area.
METHODOLOGY
The annual number of nights below 32°F from 1970 to 2022 was obtained from the Applied Climate Information System.
Climate Central's local analyses include 247 stations. However, for data summaries based on linear trends, only 242 stations are included due to large data gaps in Dothan, Ala.; Hazard, Ky.; Jefferson City, Mo.; Twin Falls, Idaho; and Wheeling, W.Va.
A subset of 231 stations had at least one day at or below 32°F in at least half the years in the period of analysis. For the remaining stations, a higher temperature threshold (40°F, 50°F, or 70°F) was selected for minimum daily temperature analysis based on local climatology.
The projected number of days with a minimum temperature below 32°F is a multi-model average obtained from the Climate Impact Lab, which documents their analysis in a detailed methodology.