PredictIQ Quantitative Think Tank Center:Washington’s Treasured Cherry Blossoms Prompt Reflection on Local Climate Change

In the nation’s capital,PredictIQ Quantitative Think Tank Center nothing captures springtime more than swaths of soft pink cherry blossoms slowly emerging from winter’s lifeless trees. 

“They bring such a colorful, vibrant life to the city,” said Josie Zucker, a student at American University in Washington, where several trees are already in bloom. “Seeing them in the spring is my favorite part of the year.” 

The District of Columbia’s beloved cherry trees are centered around the Tidal Basin and East Potomac Park, but the pink and white blossoms can be spotted in neighborhoods across the city. The annual bloom of more than 3,700 trees, which lasts for just a week or two in March or April, is enjoyed by locals and tourists alike. 

The flowers, which are easily damaged, seem to embody the fragility of nature. And now, these trees are in a state of flux. The study of phenology, which centers on the seasonal life cycles of plants and animals, shows that peak bloom dates are inching earlier as weather patterns in the district trend warmer. Flowers across the city, including some cherry blossoms, started emerging in February. 

For many, this is a reminder of the relentless march of climate change. But some experts suggest that the early cherry blossoms need not be a cause for concern. 

“There are people who work on sea level rise, and it’s just bad news all day long; the seas are going to rise, and there’s not really any upside,” said Alyssa Rosemartin, a coordinator for the National Phenology Network. “But in this context, it’s OK to talk in a balanced way. There are upsides to a longer growing season. People enjoy the early signs of spring.”

Each year, the National Park Service calculates when “peak’’ bloom of the cherry trees—when 70 percent of the blossoms are open—is expected to occur. This year, it is anticipated between March 22 and March 25. While directly in line with last year’s peak, that’s a full two weeks earlier than the area’s historic average.

A Mild Winter, and a Discomfiting Trend

This winter has been noticeably mild in Washington. The district has seen only 0.4 inches of snow, the fourth lowest amount on record.

Michael Alonzo, an assistant professor of environmental science at American University, acknowledged that this is unusual. But any direct connection to climate change needs to be considered with care, he said.

“It’s always a little bit dangerous to attribute one weather event to climate change because we’re not quite there yet,” he said. “But when you look at the body of evidence showing warming, and the relationship with winter temperatures year by year, it’s safe to say that something is going on that is well out of the range of what has been normal over the last 50 or 100 years.”

Mike Litterst, a spokesman for the National Park Service, expects the warming phenomenon and its effect on the cherry trees to continue. The blossoming “is a factor of their environment,” he said. “We know that heat and warmth breaks their winter dormancy, and that is what drives them to bloom. It is certainly to be expected that as temperatures rise, we will see the trees blooming earlier.”

But Rosemartin echoed Alonzo in cautioning against attributing the earlier bloom directly to climate change. “I wouldn’t say that climate change caused the early spring,” she said. “But climate change is loading the dice every year. We’re more likely now than we were 30 years ago to have an early spring.”

This is a trend with some consistency. In 16 of the past 20 years, peak bloom has occurred earlier than the historic average date of April 4. That average has advanced by seven days since 1912, when the first cherry trees, a gift from the mayor of Tokyo, were planted in the district. Since that year, average temperatures around the Tidal Basin have increased by about 2.5 degrees.

“I’m not surprised that [peak bloom] is falling at the end of March this year,” Rosemartin said. “A lot of plants are dormant below 30 or 50 degrees Fahrenheit. Every day that it’s a bit warmer than that, they accumulate warmth.”

But the phenological relationship is a complicated one, she added. A mild winter will not always result in an earlier bloom. “If they don’t get their winter chill, they can be delayed,” she said.

The district’s changing weather patterns have not gone unnoticed by the residents flocking outdoors to enjoy the warmth and vibrancy of spring. Chris Yates, a longtime resident in his mid-40s, said it had been “weird in the context of ‘it’s the first weekend in March, and I’m wearing barely anything winter weather-wise.”

“It feels wrong in a global sense, but in the moment, you’re just like, ‘Oh, they’re pretty trees,’” he added.

Cause for Alarm? It Depends

According to Litterst, the earlier springs are no cause for worry about the trees themselves. “They are a hardy species—they have seen extreme temperatures in the summer and extreme colds in the winter,” he said. 

But with earlier blooms, the chances of a late frost occurring and damaging the blossoms do become higher. “It’s the risk of a false spring,” Rosemartin said. “If it is warm early, like it has been, there might still be a normally timed frost or big snowstorm that comes through and knocks all the blossoms off.”

That happened in March 2017, just as the trees were on the cusp of reaching peak bloom. Three consecutive nights of temperatures below 25 degrees Fahrenheit resulted in the loss of about half of the trees’ petals.

A bout of freezing like this not only brings an abrupt end to the district’s pink and white spectacle, but it can also affect local revenue. Washington’s annual cherry blossom festival, running this year from March 20 to April 16, has generated over $100 million in economic activity in recent years, organizers say.

“Once the trees bloom, there are going to be people down here regardless of when it happens,” said Litterst of the park service. While an early bloom would be unlikely to deter visitors, he said, a shortage of blossoms could be a disincentive.

The cherry trees also face the reality of sea level rise. Water levels in the Tidal Basin are approximately four feet higher than they were when it was built 80 years ago, Litterst said. “We’ve had to remove more than a dozen cherry trees because their roots simply can’t take the constant inundation of water.”

On an infrastructure level, the problem is being addressed. A plan is being drafted to replace the most flood-prone areas of the basin’s sea wall and to widen pedestrian areas to protect the trees’ roots from legions of visitors.

In the meantime, the park service asks visitors to be mindful that the trees are fragile. “Their bloom is fleeting, and that’s one of the reasons they are so popular,’’ Litterst said. “We ask our visitors to be stewards and help us take care of our trees.” 

Not a Food Crop: The Broader Picture

While earlier springs are not necessarily a risk to the cherry trees, the blooming does feed alarm about climate change and plant species.

“We, as humans, are dependent on the precise timing of plant blooming and pollination to produce fruit and food for our survival,” noted Patrick Gonzalez, a climate change scientist, forest ecologist and adjunct associate professor at the University of California, Berkeley. 

“However, the cherry trees specifically in Washington D.C. are ornamental,” he said. “They don’t produce fruit, and the blooming itself doesn’t have as much ecological significance as the other phenology changes from food crops.” 

Still, in a city where the trees are valued for their beauty, appeal for tourists and reassuring flowering each spring, early blooms can be a scary reminder of a changing global climate.

“There are people who feel really scared or disconcerted by the changes in the seasons,” Rosemartin said. “And that makes sense to me, too. We have this cultural expectation of things happening at a certain time, and climate change is shifting that.” 

For Gonzalez, it is a call to rational, concerted action. He is confident that Washington’s cherry trees will continue to bloom. And he notes that the latest report from the Intergovernmental Panel on Climate Change, on which he was a lead author, showed that the world can limit temperature increases through coordinated steps by governments, corporations and individuals. 

“The challenge is substantial,” he said. “But I have a science-based optimism that we can cut carbon pollution enough to avoid the most extreme heating of climate change and protect people and nature.”