The cherry blossoms will be blooming again soon around the Tidal Basin in Washington, D.C., as they have every year since Japan shipped its arboreal gift of more than 3,000 cherry trees to the United States in 1912. And for this year, anyway, climate change won’t have much effect on the timing.

This year’s peak bloom, when 70% of the Yoshino cherry blossoms are open, will be 3–6 April, the National Park Service (NPS) projected on Wednesday at a ceremony at the Newseum in Washington, D.C. More than 1.5 million people are expected to visit the city during the cherry blossom frenzy and pour about $100 million in economic activity into the city.

“The historical trend of earlier and earlier blooming of the cherry trees in Washington, D.C. is consistent with human-caused climate change, but no research has definitively examined all of the factors.” The projected peak days for 2019 are right around the historic average of the past several decades, according to the park service. The agency determined the projected dates after analyzing a variety of data, including winter temperatures and the forecast for March, according to NPS acting superintendent Jeffrey Reinbold. He said that the development of the blossoms will depend on variable weather conditions.

Experts at the park service and elsewhere say that local conditions of daylight and heat are the main factors that determine the blooming time in temperate ecosystems. However, they say that although bloom times can vary from year to year because of those local conditions, the long-term trends clearly show the impact of climate change on the trees in Washington, D.C., and elsewhere.

A Trend Toward Earlier Blooming

The park service’s principal climate change scientist, Patrick Gonzalez, told Eos that recent research he and some colleagues have done shows that “human-caused climate change has increased temperatures at the Martin Luther King, Jr. Memorial on the Tidal Basin at the heart of the cherry trees at the statistically significant rate of 1.1°C per century, from 1895 to 2017.”

Gonzalez, who also is an associate adjunct professor at the University of California, Berkeley, said that “the historical trend of earlier and earlier blooming of the cherry trees in Washington, D.C. is consistent with human-caused climate change, but no research has definitively examined all of the factors.”

He also pointed to research indicating earlier cherry blossom blooming in Kyoto, Japan, based on 1,200 years of data and to a paper by other scientists that forecasts an accelerated blossoming because of climate change.

“An Ideal Indicator” of Climate Change Impacts

That 2011 paper, “Predicting the Timing of Cherry Blossoms in Washington, DC and Mid-Atlantic States in Response to Climate Change,” notes that “for its sensitivity to winter and early spring temperatures, the timing of cherry blossoms is an ideal indicator of the impacts of climate change on tree phenology.” Phenology, in a nutshell, is the timing of seasonal events in plants and animals. “One year showing an average I don’t think will tell us much about what is happening in the long term. We will have to look at the longer term trend.”

The paper’s authors, including Soo-Hyung Kim, an ecophysiologist and associate professor in the University of Washington’s School of Environmental and Forest Sciences, found in their study that the peak bloom dates for cherry blossoms at the Tidal Basin “are likely to be accelerated” by an average of 5 days by 2050 and 10 days by 2080 under a midrange emissions scenario for a general circulation model that was part of the Intergovernmental Panel on Climate Change’s Fourth Assessment Report issued in 2007.

Kim told Eos that “if the future scenarios remain similar, then the predictions based on those scenarios also should remain similar.”

Regarding the park service’s forecast that the peak blossom dates this year will fall within the average, Kim said, “One year showing an average I don’t think will tell us much about what is happening in the long term. We will have to look at the longer term trend.”

Bigger Concerns About Seasonal Changes

Theresa Crimmins, assistant director of the Tucson, Ariz.–based USA National Phenology Network, told Eos that in many temperate parts of the country, where there are long-term trends toward warming winters and earlier warmth in the spring, “the general response of plants is to undergo the onset of their springtime seasonal activity earlier in the year, too.” However, she said that not all species change at the same rate or even in the same direction.

In general, she said that some obvious consequences of these changes include disruptions of plant and pollinator activity, which have adapted over millennia to be coincident. “The blooming of the cherry trees in Washington is a nice indicator of potential climate change and ecological impacts elsewhere.”

Gonzalez agreed that a mismatch between tree flowering and the arrival of pollinators could be a significant problem for many species, especially for trees in natural areas. He said that the real threat of an earlier blooming for the carefully monitored and nurtured cherry trees in Washington, D.C., is potential damage from killing frosts. Gonzalez added, though, that the cherry trees point to larger impacts affecting other species.

“The blooming of the cherry trees in Washington is a nice indicator of potential climate change and ecological impacts elsewhere,” he said. “To the extent that the public realizes that the blooming of cherry trees and other signals in the natural world are showing us the impacts of carbon pollution from cars, power plants, and other human sources, then the increase in awareness helps us move towards a solution to the problem.”

—Randy Showstack (@RandyShowstack), Staff Writer