Cherry Blossoms

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4 Apr 2024

Did you enjoy the cherry blossoms' early peak bloom? It was a warning sign.

A 1,200-year record of cherry blossoms shows our current climate is historically unprecedented.

First, the green bud appears, sprouting from a tree branch like a fledgling peering skyward from its mother’s nest.

The florets show up next, extending from the branch’s center like a petal unfurling to bask in the sun. This is followed by the elongation of a smattering of flower stalks, from which a handful of puffy cherry blossoms finally open in a dazzling bloom.

Lured by the spellbinding visual and the chance to catch a whiff of the flowers’ almond-like scent, Kyoto’s blooming cherry blossoms—or sakura—draw crowds from across the world. But around when the delicate buds that adorn Kyoto’s cherry trees bloom in springtime has advanced by nearly two weeks from when they used to emerge in 1850.

That timing is one of the most valuable benchmarks for scientists tracking the impacts of climate change on flowering plants. “We are now blowing by any experienced climate that we've ever seen as human beings,” said Elizabeth Wolkovich, an associate professor at the University of British Columbia who studies plant communities and climate change.

Global warming, largely driven by fossil fuel combustion, propelled temperatures so high in 2023 that it became the hottest year in history, followed by the warmest January and February on record.

“To me, the cherry blossom record really captures how extreme these changes are,” she said. A co-organizer of the International Cherry Blossom Prediction Competition, Wolkovich says that anthropogenic climate change is driving earlier springs, which is leading to early-blooming cherry blossoms in locations like Kyoto.

“We haven't experienced anything like this,” said Wolkovich. “It really dwarfs the Little Ice Age or the Medieval warm period…it's a new world that we are heading into.”

Peak bloom arrives early

Warmer springs triggering earlier blooms is a phenomenon not just isolated to Kyoto’s renowned sakuras, but something scientists are also observing elsewhere—including in Washington D.C.

On March 17, the signature cherry trees in the nation’s capitol saw their second-earliest peak bloom on record—emerging almost a week before they were expected to, tying with the year 2000, per data from the EPA.

Peak bloom, or the point at which nearly two-thirds of a tree’s blossoms open, typically lasts at least a week, but varies depending on weather conditions and species. Sometime between the end of March and beginning of April has historically been when the Yoshino Cherry, the type of tree found throughout D.C., experiences peak bloom—but scientists believe that’s changing in response to the planet’s rapidly warming temperatures.

Although flowering times vary annually, the long-term trend shows earlier blooming in D.C., according to Patrick Gonzalez, a climate change scientist and forest ecologist at the University of California, Berkeley.

“In D.C., the advance in blooming is consistent with, but not scientifically attributed to, human-caused climate change,” said Gonzalez. This means that while scientists have detected a change that is statistically different from natural variation, they haven’t yet attributed it to anthropogenic climate change. Other possible causal influences include the urban heat island effect, he noted.

That's where the research in Kyoto is critical. The city’s sakura records go back more than 1,200 years—offering up a treasure trove of historical weather data that has been described as likely the longest annual record of phenology, or the study of biological life cycles, anywhere on Earth.

And unlike in D.C., research on earlier blooms in Kyoto “has been both detected and attributed to human-caused climate change,” said Gonzalez.

In 2020, 2021, and 2023, Kyoto’s sakura saw record-early blooms—the earliest dates ever recorded, reported the BBC. A 2022 study found that anthropogenic climate change is the primary reason behind an earlier spring ushering in the “peak bloom” flowering period in Kyoto, pushing that season forward by roughly 11 days.

Under a medium-emissions scenario, the research estimates that Kyoto’s cherry blossoms' earlier arrival would push forward by almost another week by 2100. To some, this pattern should be viewed with a sense of alarm.

“This is one of the most visible signs to people of the impacts of excessive human carbon pollution,” said Gonzalez, adding that continued climate change could advance cherry tree blooming even further under a “worst case” emissions scenario. “It really signals how seriously we need to cut our carbon pollution to reduce the most drastic impacts of climate change.”

Why early blooms matter

The early onset of spring and subsequent accelerated cherry tree blooms can result in ecological disruptions that include blossoms mismatching with their pollinators and an increased cold snap vulnerability afflicting the trees themselves.

While they may not produce edible fruit, the impacts of climate change on cherry blossom trees also provide a fitting example of what other crop-producing trees—such as apples and peach blossoms—are simultaneously undergoing, according to Lewis Ziska, a plant physiologist and associate professor at Columbia University.

And if winter continues to warm faster than summer in much of the U.S., the amount of exposure to cold weather that a tree requires in its winter dormancy period may not be met—resulting in some trees failing to flower at all in the spring.

A cherry blossom tree needs a month of temperatures below 41 degrees Fahrenheit to fully bloom during warmer weather. In cherry blossom hotspots like D.C., a recent analysis of National Park Service data shows that the average spring temperature in D.C. has increased 3.6 degrees Fahrenheit from 1970 to 2023. In 2017, a late frost killed roughly half of the trees’ blossoms.

“[Peak bloom date] may be accelerated in the future,” said Ziska. “But the end result of not having any blossoms, if there's no winter, may happen sooner than we think.”

“A spiritual feeling”

Not only are cherry trees a tool for scientists to understand changing temperatures, but the trees’ flowering also represents a “very visible” historical and cultural symbol for people to celebrate the onset of spring, said Soo-Hyung Kim, a plant ecophysiologist and professor at the University of Washington.

“The arrival of spring is a feeling…there’s just warmth around it,” said Kim, adding that the “spectacular” experience isn’t limited to Kyoto and D.C. A grove of flowering cherries in Seattle, which also recently hit peak bloom, is among the dozens of sites where the blossoms’ splendor can be witnessed nationwide—a list that includes everywhere from a botanical garden in St. Louis, Missouri to an annual festival in Macon, Georgia.

For those who haven’t had the opportunity to stroll under a canopy of blooming cherry blossom trees, Ziska says the experience is akin to “walking through a church or cathedral.”

“You can imagine colors. Pinks of all shades, reds of all shades, and the blue sky behind them. And at some point the words don't apply…there are not words to describe it,” said Ziska. “It's a spiritual feeling. It touches a part of your soul that can't be reached any other way.”