Warm Winter Days Boosted by Climate Change in U.S. Cities

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KEY CONCEPTS

• Carbon pollution drove abnormal warmth this winter. New Climate Central analysis shows which U.S. cities, states, and regions felt the strongest influence of climate change on daily average temperatures between December 2023 and February 2024.

• In the U.S., 283 million people — about 85% of the population — experienced at least one winter day with warm temperatures made at least two times more likely due to human-caused climate change. 

• Of the 247 U.S. cities analyzed, 51% (127) experienced five or more winter days with a Climate Shift Index level 2 or higher — indicating warm average temperatures made at least two times more likely by climate change.

• U.S. cities with the most warm winter days made at least two times more likely by climate change were: San Juan, Puerto Rico (84 days); Honolulu, Hawaii (50); San Francisco, Calif. (39); Juneau, Alaska (37); San Jose, Calif. (35); and Duluth, Minn. (33).

• Over the last three months, midwestern cities were among the most unusually warm in the world. Of the 487 global cities with populations larger than 1 million analyzed, Minneapolis experienced the largest departures from its normal winter temperatures (10°F warmer than average). Cities across the Upper Midwest experienced strong climate fingerprints on temperatures this winter, which also saw near record-low Great Lakes ice cover.

• Warming winters have year-round effects on seasonal allergies, lake ice, water supplies, and more.

Download data: Climate Shift Index and winter warming in U.S. cities, December 2023-February 2024

This brief focuses on U.S. states and cities. Check out the full report Seasonal Attribution Report for a global analysis of temperatures boosted by climate change from December 2023 to February 2024

Global fingerprints of climate change

Carbon pollution, primarily from burning fossil fuels, drove abnormal warmth this winter. 

Over the last three months, cities across the globe experienced warmer-than-expected temperatures that were strongly influenced by human-caused climate change, according to Climate Central’s Climate Shift Index (CSI).

• Roughly 80% of Earth’s population, 6.7 billion people, were exposed to abnormal warmth linked to climate change between December 2023 and February 2024.

• Learn more: Seasonal Attribution Report

New Climate Central analysis used the Climate Shift Index to quantify the influence of human-caused climate change on daily average temperatures experienced in 247 U.S. cities during meteorological winter in the northern hemisphere (December 1, 2023 to February 29, 2024). See Methodology below for details.

Climate Central’s Climate Shift Index, grounded in peer-reviewed attribution science, is based on the relative frequency of daily temperatures in the current climate and in a world without human-caused climate change. High Climate Shift Index levels mean that climate change made the temperatures more likely. For example:

• A Climate Shift Index level 2 indicates local temperatures that were made at least two times more likely due to climate change. These conditions indicate a strong influence of human-caused climate change. 

• A Climate Shift Index level 5 indicates local temperatures that were made at least five times more likely due to climate change, and potentially far more. These are exceptional events driven by human-caused climate change. 

For more information about the Climate Shift Index: watch our video explainer, explore the FAQs on our website, or read our peer-reviewed methods paper.

Influence of climate change during winter in U.S. cities

Across the U.S., 283 million people — 85% of the population — experienced at least one winter day with warm average temperatures made at least two times more likely due to human-caused climate change.

Of the 247 U.S. cities analyzed, 51% (127) experienced five or more winter days with a Climate Shift Index level 2 or higher — indicating warm average temperatures made at least two times more likely by climate change. 

Around half of all the U.S. cities analyzed (121) experienced average winter temperatures at least 3°F above normal.

U.S. cities with the strongest fingerprints of climate change, December 2023 to February 2024:

Midwestern cities felt the strongest influence of climate change.

In Minnesota, winter average temperatures in both Minneapolis and Duluth were more than 10°F above normal. People in both areas experienced more than 30 days of winter warmth made at least twice as likely by carbon pollution (Climate Shift Index level 2).

Daily temperatures in Minneapolis reached Climate Shift Index level 5 on three days this winter — indicating that climate change made those warm daily temperatures at least fivetimes more likely. Temperatures on those days would have been virtually impossible without the influence of carbon pollution.

Other midwestern cities experienced a strong influence of climate change:

• Residents of Marquette, Michigan and Mankato, Minnesota experienced more than 25 days with temperatures at Climate Shift Index level 2 or higher — contributing to average temperatures that were at least 9°F above normal for each city.

• In Wisconsin, Green Bay and Milwaukee experienced more than two weeks worth of warm winter days made at least twice as likely by climate change. 

• Detroit, Mich., Chicago, Ill., and Cleveland, Ohio all experienced at least seven days at Climate Shift Index level 2 or higher.

The Midwest’s winter warmth stood out on a global scale, too. Among the 487 global cities (with populations of at least 1 million people) included in the full analysis, Minneapolis experienced the largest warm departures from its normal winter temperatures (10°F).

The region’s unusual winter warmth boosted by carbon pollution coincided with record low Great Lakes ice cover — part of a decades-long trend toward less ice, for less time.  

The Great Plains also experienced strong climate fingerprints.

Winter temperatures in Fargo, North Dakota were more than 10°F above normal. The city saw 32 days at Climate Shift Index level 2 or higher — meaning climate change made these abnormally warm winter temperatures at least twice as likely.

Bismarck, North Dakota and Sioux Falls, South Dakota experienced more than 10 winter days with warm temperatures made at least twice as likely by climate change. Average winter temperatures were around 6°F above normal in Bismarck and 8°F above normal in Sioux Falls.

The impacts of climate change were felt beyond the contiguous U.S.

San Juan, Puerto Rico experienced more days influenced by climate change (at any Climate Shift Index level) than any other U.S. city. San Juan saw at least 84 winter days at Climate Shift Index level 2 or higher, and 65 of those winter days reached level 5.

Honolulu, Hawaii experienced 52 winter days with temperatures made at least twice as likely by climate change, with 25 of those days that Climate Shift Index level 5.

Juneau, Alaska experienced at least 35 days at Climate Shift Index level 2 or higher, and 10 of those days reached level 5. Temperatures on those days would have been virtually impossible without the influence of carbon pollution. The city’s winter temperatures were more than 4°F above normal.

Western states didn’t escape the warming influence of climate change.

In California, San Francisco and San Jose both experienced more than 30 days with temperatures made at least twice as likely by climate change. When daily temperatures were averaged over the entire three-month period, however, winter average temperatures were only slightly above normal for both cities. It is worth noting that the 1991-2020 period used to define normal already includes 1.6°F of global warming relative to the late 1800s. San Francisco experienced more days that reached Climate Shift Index level 5 (12 days during the analysis period) than any other city analyzed in the contiguous U.S.

In the Pacific Northwest, Seattle, Washington experienced more than 25 days at Climate Shift Index level 2 or higher, while Portland, Oregon had nearly two weeks worth of temperatures made at least twice as likely by climate change.

East Coast cities felt the warming effects of carbon pollution, too. 

In the Northeast, people in Albany, N.Y., Boston, Mass., and Burlington, Vt. saw at least seven days that reached a Climate Shift Index level 2 or higher. Boston residents experienced winter temperatures more than 3°F above normal, while temperatures in Albany and Burlington were around 6°F warmer than their city’s seasonal average.

Winter temperatures in New York, New York were nearly 4°F above normal. Climate change made warmer temperatures at least twice as likely on eight winter days.

The effects of winter warming can last all year. 

Winter is the fastest-warming season for most of the U.S., and unusually warm winter days now happen more often. Winter warming has year-round effects that can:

• Contribute to longer growing seasons and longer allergy seasons.

• Increase the likelihood of ice-free lakes — which can influence lake water levels and lake-effect snow and have cascading impacts on cultural heritage, ecosystems, and recreation. 

• Disrupt the chill that valuable fruit and nut crops depend on.

• Change the timing, location, and amount of snowfall — as well as spring snowmelt and water supplies.

• Decrease home heating demand, which can be offset by longer, higher cooling demand during warm seasons. 

LOCAL STORY ANGLES

Climate Shift Index tools, data, custom maps, and local alerts

Here are four ways to use this attribution analysis from Climate Central:

Use the tools. Climate Central’s Climate Shift Index map tool shows which parts of the world are experiencing high Climate Shift Index levels, every day. Explore the global Climate Shift Index map for today, tomorrow, and any day.

Download the data. Data from this analysis are available to download and explore in more detail the daily global population exposure to high Climate Shift Index levels, and summary conditions for 175 countries and 678 cities between December 2023 and February 2024.

Access KML to create custom Climate Shift Index maps. The Climate Shift Index is now available in KML format. Fill out this form to join our pilot project, receive the KML links, and create custom Climate Shift Index maps. 

Sign up for alerts. Sign up here to receive custom email alerts when strong Climate Shift Index levels are detected in your local area.

CONTACT EXPERTS

Andrew Pershing, PhD (he/him/his)
VP for Science
Director of Attribution Science and Climate Fingerprints
Climate Central
Relevant expertise: Climate change attribution
Contact: pgirard@climatecentral.org (Peter Girard, VP for Communications)

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

All Climate Shift Index (CSI) levels reported in this brief are based on daily average temperatures and ERA5 data from December 1, 2023 to February 29, 2024 for 247 U.S. cities. See the frequently asked questions for details on computing the Climate Shift Index, including a summary of the multi-model approach described in Gilford et al. (2022).

For local graphics included in this brief: Daily average temperature anomalies (relative to 1991-2020 normals) were obtained from the Applied Climate Information System (ACIS) for 242 stations from December 1, 2023 to February 29, 2024. While Climate Matters local analyses typically include data from 247 stations, five were excluded from this analysis due to insufficient data: Bend, Ore.; Glendive, Mont.; Idaho Falls, Idaho; Laredo, Texas; and Panama City, Fl.