Winter is warming almost everywhere. See how it’s changed in your town.
As another winter nears its close, we bid farewell to the season of merriment, good cheer and inane arguments about global warming.
If you think global warming is nonsense, winter offers many cold things to gesture at. “Behold,” you will say, brandishing a snowball, “global warming is a lie.” If, on the other hand, you’re terrified of global warming, you might startle at its shadow. A single unseasonably mild day becomes just more proof that the world is ending.
Fortunately, we don’t need to depend on people’s fears and vague intuitions to know how winter is changing. For that, we have high-resolution temperature data. In fact, I can tell you that in 86 percent of the contiguous United States, winters are trending warmer since 1980.
New England winters are warming fastest. The precise reasons are unclear, but warming Atlantic Ocean water could be making northeast winters milder, experts say. And warming winters feed on themselves. With less ice and snow reflecting sunlight back to space, the land absorbs more heat, driving temperatures higher.
In my Connecticut hometown, the average winter temperature used to be slightly below freezing. Now, it’s slightly above. How many joyful days filled with snowball fights and sledding would I have instead spent suffering in a classroom, gazing out the window at the rain, imagining the world just a little colder?
In Dover, Vt., home of the Mount Snow ski resort, winters have warmed at a rate of 1.19 degrees Fahrenheit per decade. “Being uniquely tied to the outdoors, we take climate change and its impacts on our industry extremely seriously,” said Joe Healy, a spokesperson for Vail Resorts, Mount Snow’s parent company.
Part of that means taking snow-making extremely seriously. Mount Snow can turn 100 acres of bare mountain into snowy, skiable slopes in little more than a day, Healy told me. The resort also sells as many preseason passes as it can, which can cushion the financial blow of a ski season without much snow.
What about the 14 percent of the country where winters are getting colder?
The simplest explanation is randomness, said Ken Kunkel, a senior scientist with the North Carolina Institute for Climate Studies. “Spatial variability is a natural part of the climate system,” Kunkel said. “I would actually be more surprised if you had found that the trends were the same, or nearly the same, everywhere.”
Still, over a 45-year period in which nearly the entire planet has warmed, why do we find any cooling trends at all? And why in the western United States but not in the east?
One theory involves the polar vortex, a cyclone of stratospheric winds that swirls over the North Pole, waning in summer and growing stronger in winter. As the Arctic has warmed, the polar vortex has grown wobblier during winter, sometimes spilling south into the United States.
Crucially, the Arctic polar vortex spins counterclockwise. When it descends into lower latitudes, its western side brings cold air from the north while delivering milder southern air to its eastern side. This could have slowed the rate of warming in the west while having little impact on the east.
The polar vortex theory is still up for debate. Whatever the cause, something is stopping western winters from warming like the rest of the country. In northeastern cities like Boston and Burlington, Vt., winters have warmed by more than 1 degree Fahrenheit per decade, while winters in Los Angeles are barely warming at all. In San Diego, winters have been getting slightly colder.
Or hover on the chart to explore the data| Change per decade | |
| Population |
In colder areas, milder winters can cut energy bills and reduce cold-related deaths, which outnumber deaths from heat by a wide margin. But warmer winters have their drawbacks, too. Disease-carrying insects like mosquitoes and deer ticks can remain active for longer, and invasive plants like kudzu thrive in areas with milder weather.
Have you perceived long-term changes in winter where you live? If so, I’d love to hear from you. You can email me at harry.stevens@washpost.com.
Check my work
I downloaded daily minimum and maximum temperature data from GridMET. To get the approximate daily mean temperature, I divided the sum of the daily minimum and maximum temperatures by two. Then I calculated the average daily temperature for each winter, beginning from Dec. 1 of the previous year and ending Feb. 28 of the current year. For example, winter 1980 begins Dec. 1, 1979, and ends Feb. 28, 1980. Finally, I calculated the linear regression relating time to temperature in each grid cell.
Each of those grid cells is 1/24 degrees, or a little more than 8 square miles. To join the grid to a list of cities, I downloaded the locations and populations of cities from Simplemaps. Then, I found the grid cell containing each city’s coordinates, filtering out a handful of cities in the Florida Keys that did not fall within the bounds of any grid cell.
The code I wrote to generate this article’s graphics can be found in three computational notebooks: the map, the trend chart, and the “wartplot” showing cities by winter temperature trend, region and population.
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