How many times in recent years do you recall ambling outside in 70-degree weather totally bewildered during the winter months?
Over the past five decades, the region has seen winter average temperatures increase between three and five degrees.
Based on current projections from the University of Maryland Center for Environmental Science, the winter months could warm an additional 4 to 10 degrees by 2080, depending on emissions of heat-trapping greenhouse gases and how the climate responds to them.
So far, warming is evident in each of the winter months, and the season is shrinking. Winter weather is starting later, ending earlier and is less intense at its peak. These changes are in line with observations nationwide that match what climate scientists expect in a world that is warming as a result of burning fossil fuels, such as coal and natural gas, for energy.
The data is stark
Since 1970, Washington’s average winter temperature has risen 2.9 degrees from an average of 37.2 degrees in 1970 to 40.1 during the winter of 2019-2020. The change has been even more pronounced at Dulles International Airport, with the average winter temperature increasing by 4.4 degrees, from 32.8 degrees in the winter of 1969-70 to 37.2 last winter.
In addition to long-term climate change from increasing greenhouse gases, there has been a marked increase in urban development in and around Dulles Airport, which may also be intensifying its rate of warming.
The frequency of bitterly cold winter days is in decline. During the past five decades, Washington has seen the number of days with high temperatures below freezing fall from an average of about 10 to 6 per year. At Dulles, the count has dropped from roughly 16 to 10.
Nights are thawing. In 1970, Washington would see lows dip to 32 degrees or lower 70 times in an average year. That number has dropped to 55, as of 2020. Dulles saw an average of 120 days with low temperatures at or below freezing in 1970, compared with 95 today.
The length of the season with freezing temperatures is shrinking. In the past five decades, the average length of time between Washington’s first and final freeze has decreased by about three weeks. At Dulles, where the freeze season is longer, the decline is sharper, down an entire month since 1970.
Extreme cold is no longer as extreme as it once was. In Washington, the lowest temperature of the year has risen from an average of 9 degrees in 1970 to 14 degrees today. At Dulles, it has increased from an average of minus-5 degrees to 6 degrees in this same span.
The last time the temperature in Washington fell below zero was in 1994. Of the 32 instances of subzero temperatures in Washington’s climate history, 29 of them occurred before 1940.
It’s not just Washington that is seeing winters get shorter and less severe. Climate Central, a nonprofit climate research and communications group, looked at winter temperature trends in 49 states since 1970 and found that winter is the fastest-warming season in 38 of them, especially in the Midwest and Northeast.
According to Zeke Hausfather, director of climate and energy at the Breakthrough Institute, winters are warming faster than other seasons because of the role water vapor plays in accelerating warming.
“Water vapor is a powerful climate feedback; with warmer temperatures there is more moisture in the air, and water vapor itself is a powerful greenhouse gas,” Hausfather said in an email. “In the winter — when water vapor in the atmosphere tends to be lower — an increase in the amount of water vapor in the atmosphere has a larger warming effect than in the summer, when there is already a lot of water vapor.”
Warmer winters won’t be snowless
Even though Washington is seeing a pronounced warming trend during the winter, this doesn’t mean that it will cease to snow anytime soon. It can still snow in a warming climate, sometimes quite a lot.
During January 2016, D.C. featured its fourth-biggest snowstorm on record, at 17.8 inches. While January was slightly below average temperature-wise that month, the winter as a whole was 10th-warmest, with an average temperature of 42 degrees. In addition, that winter’s December was the warmest on record.
In Washington’s snowiest winter on record, in 2009-10, winter ended abruptly after 56.1 inches of snow. The final freeze that winter was Feb. 27, which is the earliest final freeze on record. Last winter, Washington posted its second earliest last freeze on March 1.
Overall, the relationship between temperatures and snow is straightforward. Increasing temperatures and shorter winters mean that we have fewer chances at a significant snowstorm, but they don’t eliminate the possibility.
As Brian Brettschneider, a climatologist at the University of Alaska at Fairbanks, wrote in a tweet earlier this year, “At the weather time-scale, a big snow event can occur in an otherwise warm winter, but at the climate scale, more warm days means fewer opportunities for snow.”
It’s not surprising, then, that seasonal snowfall is declining in Washington. The National Oceanic and Atmospheric Administration (NOAA) maintains 30-year climate averages, and these are set to be updated next year to cover the period from 1991 through 2020. Once NOAA makes this switch, the average snowfall in D.C. will fall from 15.4 inches, which is the current normal amount when using the 1981-2010 period, to less than 14 inches.
Sights that once were common in Washington, such as the Potomac River freezing over as it curves its way through the District, are increasingly rare. So too are freezes for parts of the Chesapeake Bay.
In February, instead of river ice, we now have pollen spikes and earlier insect hatchings.
In addition, cherry blossom data shows that the average peak bloom has moved from April 4 to March 31 since 1921. This is primarily because March temperatures have risen over time.
Feeling like the South
There’s a long debate about whether D.C. is part of the South. One thing is certain, our new winter climate will surely feel that way.
The University of Maryland’s Center for Environmental Science created an interactive tool that projects how the climate of cities across North America is expected to shift over the next 60 years due to emissions of heat-trapping gases into the atmosphere.
Washington’s winter climate now resembles Richmond’s from about 100 years ago, and may end up resembling locations in Mississippi or South Carolina as climate change continues.
Under both the current high emissions and reduced emissions scenarios, our climate is expected to become more like the South. In a high-emission scenario, our climate match would be Greenwood, Miss. In a lower emissions future, D.C. could more closely resemble Paragould, Ark.
As our current climate shifts southward (or Southern climates shift northward, depending on your perspective), areas to our north like New York City are expected to become the new Washington during the winter and year-round.
