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What Washington’s famous cherry blossoms can teach us about climate change

Lauren Katz is a project manager at Vox, focusing on newsroom-wide editorial initiatives as well as podcast engagement strategy.

Spring in Washington, DC, means cherry blossom season, and the explosion of color around the Tidal Basin near the National Mall. This year, spring is arriving early, not just in Washington, but in a broad swath of the country. A quick Twitter search for photos of cherry blossoms in the DC area show how the trees are already beginning to bud and bloom.

The National Park Service recently updated its forecast for peak cherry bloom bloom; it's now expected March 19-22, which is about a week and a half earlier than the average date of April 1. Peak bloom, when 70 percent of the trees' blossoms are open, happens at a slightly different time every year.

And it's hard to predict. The dates depend heavily on the weather in the months leading up to April, according to the NPS bloom watch:

(National Park Service)

Vox recently spoke via email with Patrick Gonzalez, Principal Climate Change Scientist of the U.S. National Park Service and Visiting Scholar at the University of California, Berkeley, about what the unusually warm weather of early 2017 might mean for the Yoshino cherry trees. The following interview has been edited for length and clarity.

Lauren Katz

What are some factors that contribute to early blooming?

Patrick Gonzalez

Daylight and heat are the main factors that determine blooming time in temperate areas such as the lower 48 U.S. states. In flowering trees, daylight and heat trigger the break from winter dormancy.

Lauren Katz

Is the trend of earlier blooming consistent with warming trends we're seeing? And what can early blooming tell us about climate change, if anything?

Patrick Gonzalez

In Washington, DC, weather station measurements since 1946 show a statistically significant temperature increase of 1.6 degrees Celsius per century — double the global rate.

From 1970 to 1999, a Smithsonian Institution researcher and colleagues recorded blooming dates for 100 species of flowering trees around Washington, DC. For the Yoshino cherry (Prunus x yedoensis), the most numerous of the historic cherry trees around the Tidal Basin, their published research showed a statistically significant advance of cherry tree blooming by seven days. While blooming dates vary from year to year, the long-term trend shows earlier blooming. This earlier cherry blooming is consistent with the hotter temperatures caused by climate change.

A published analysis that examines possible future trends indicates that, if we do not reduce our emissions from cars, power plants, and deforestation, additional warming could advance peak cherry tree bloom at the Tidal Basin by a week to a month by the end of the 21st century.

Lauren Katz

I'm curious what this trend could mean for the trees long-term. Are there downsides to early blooming?

Patrick Gonzalez

Right after trees bloom, their leaves fully unfold in preparation for spring and summer growth. Earlier blooming possibly increases the chance that a snow or frost might follow the leafing out of the trees, damage the leaves, and reduce the growth and health of the trees.

Many trees depend on birds, bees, butterflies, and other species to pollinate their flowers, a necessary step to the formation of fruit. For those species of trees, earlier blooming may create a mismatch between flowering and the arrival of pollinators. This could possible reduce fruit production and, for trees in natural areas, reduce the number of seedlings to grow into trees in the future.

For the cherry trees at the Tidal Basin, the National Park Service plants replacement trees grown off-site in a nursery, so the pollinator mismatch does not necessarily reduce the number of trees.

To see the blossoms in action, you can watch the live stream courtesy of the National Park Service and EarthCam, which teams up to highlight scenes from around the nation's capital.

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