Map source: Washington Post
By Dorothy Janick
This past winter in the United States was the coldest in over a decade—and yes, climate change is still happening. This week, we’re taking a closer look at the map of global temperature anomalies from December 2024 to February 2025, as compared to the thirty-year average from 1991–2020.
Overall, the contiguous United States was about 1.1° Fahrenheit (0.6° Celsius) below the 1991–2020 thirty-year average, making this the coldest winter the United States has seen since the winter of 2013 to 2014. Several states experienced extreme cold anomalies, like in western Kentucky, where some areas were almost 7 degrees colder than the thirty-year average.
These cold conditions were largely due to the expansion of the polar vortex. The polar vortex is an area of low-pressure cold air that surrounds the Earth’s poles. This winter, a high-pressure area in parts of the Arctic pushed the polar vortex farther south than usual, rerouting cold air masses. At one point, the polar vortex was pushed so far south that it encompassed parts of Louisiana, making Louisiana temperatures actually colder than in Anchorage, Alaska.
Despite these cold anomalies in the United States, global temperatures still increased significantly. In fact, January 2025 was the warmest January since human records began, surprising climate scientists who’d expected a cooler January due to modest La Niña conditions in the equatorial Pacific, which generally lead to a cooling effect on global temperatures. Compared to pre-industrial global temperatures, January 2025 showed a warm temperature anomaly of 3.15° F (1.75° C). Across the globe, 44 percent of areas experienced above-average temperatures this winter compared to the 1991–2020 thirty-year average.
This map, created by The Washington Post using data from NOAA, shows that while some areas like the United States experienced colder temperatures than usual, many other parts of the globe experienced warmer temperatures, especially in the high latitudes. The areas around the poles are the fastest-warming regions of the globe; this phenomenon is called polar amplification, and it’s a key feature of climate change. As temperatures in the Arctic continue to increase, climate models aren’t clear about how the polar vortex might respond, with some models indicating that the polar vortex will strengthen, while others indicate it will weaken, in which case we would see the polar vortex moving south even more frequently.
While this winter’s relatively cool temperatures may fuel climate change skeptics, it’s important to understand that short-term, regional variability does not negate long-term climate trends, which continue to show warming global temperatures. In addition, this winter’s temperatures in the United States were cold compared to the recent 1991–2020 thirty-year average—a useful comparison for understanding current climate conditions, but not as useful for measuring long-term climate change. If we compare this winter’s temperatures to pre-industrial temperatures, we see significant warming. The warming trend, despite short-term variability, demonstrates the ongoing impact of anthropogenic warming on our planet’s climate system.
Sources:
Hausfather, Z. (2025, February 2). “January sets an unexpected temperature record.” The Climate Brink (blog). https://www.theclimatebrink.com/p/january-sets-an-unexpected-temperature.
Noll, B. (2025, 3 March). “Why winter was colder than average in the U.S., and what spring will bring.” Washington Post. https://www.washingtonpost.com/weather/2025/03/03/coldest-winter-united-states-spring-forecast/.
Rantanen, M. et al. “The Arctic has warmed nearly four times faster than the globe since 1979.” Nature 3, (2022). https://www.nature.com/articles/s43247-022-00498-3.
National Weather Service. “What is the Polar Vortex?” (n.d.). https://www.weather.gov/safety/cold-polar-vortex.