Early cherry blossoms aren't a good climate change indicator in Washington, D.C.

Take a Break From Worrying About Climate Change to Enjoy the Early Cherry Blossoms

Take a Break From Worrying About Climate Change to Enjoy the Early Cherry Blossoms

The Slatest
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March 25 2016 2:44 PM

Take a Break From Worrying About Climate Change to Enjoy the Early Cherry Blossoms

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A young woman smells the blooms of one of the cherry trees surrounding the Tidal Basin near the National Mall on Wednesday in Washington, D.C. You should, too.

Chip Somodevilla/Getty Images

Spring is officially here: D.C.’s cherry trees are in peak bloom.

It’s a rite of seasonal passage for locals, and you can expect stunning and very spring-y photos to flood your Instagram feeds over the next several days. This year’s blossoms are arriving nearly two weeks early, thanks to several above-normal temperature days this March on the East Coast—half of the days this month have been at least 10 degrees warmer than normal in D.C. That may make for some “pretty sweet” early springtime weather, but in my circles, that means subtle expressions of existential worry about climate change.

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That specific worry is misguided. (There are, of course, countless other reasons to fret about climate change, if you feel so inclined.) But feel free to go bask in pink and white this weekend with a modicum of dread.

So why are the trees blooming early? The D.C. icons are a Japanese species, a gift of Tokyo Mayor Yukio Ozaki in 1912. The climate in Tokyo and D.C. is similar enough, but not identical. Across the Pacific, there is convincing evidence from hundreds of years of Japanese cherry blossom festivals that blooming season has been getting earlier in recent years there due to warmer temperatures. And D.C.’s cherry trees have been blooming an average of five day earlier in recent years too (though that data point doesn’t have nearly the statistical grounding as the evidence from Japan).

But D.C.’s cherry blooms are more variable at least partly because cherry trees aren’t native to the area, so it’s harder to definitively link to climate change. We do know that warmer weather makes cherry blossoms come sooner—but it’s mostly just, as a non-native species, the D.C. cherry trees are out of their natural context, so they’re not a reliable indicator. In general, this holds true for most non-native species: In 2002, the New York Botanical Garden planted an experimental border comprised of non-native species adapted to a climate similar to the one expected to arrive in New York City within the next few decades. This year, a few of those species are blooming early, too.

“It’s glorious if you like creepy early springs where everything is flowering three weeks earlier than what you’d like it to be,” Todd Forrest, NYBG’s chief horticulturist, told me. In 2012, the U.S. Department of Agriculture updated the nationwide map of plant “hardiness zones,” a key guide for gardeners, shifting the zones delineating similar climates northward. But again, farmers’ fields and gardens along sidewalks and in backyards typically have non-native plants. And non-native plants, like daffodils, magnolias, and cherry trees, have a range of flowering dates that is much bigger than non-native plants. The East Coast is a highly variable climate, and this year was “a classic winter of extremes,” Forrest said, with a few of the coldest days on record interspersed with long stretches well above normal. Last year, after a particularly cold winter, the soil in the NYBG flowerpots was still frozen at this time, Forrest said, noting that the early bloom of non-native plants doesn’t necessarily concern him.

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For true evidence of climate change in the natural world, interested observers should instead focus their attention on phenology, the study of the behavioral response of native plants and animals to weather shifts. The key difference here is the word “native”—plants that are local to the area.

Thankfully, since people have been enjoying nature throughout all of history and like writing things down, in some cases there are ample records of native species’ behavioral changes over time. Aldo Leopold and Henry David Thoreau, for example, were avid phenologists. Here, Leopold’s daughter describes her family’s fascination:

It’s when we start to see significant and widespread shifts in indigenous species that have spent eons adapting to the local environment, that we should start to worry. There’s evidence that, in some limited cases, this may already be happening.

Instead of cherry trees, Forrest said, “the real harbinger of spring is the red maple.” Since 2001, the NYBG has had a citizen-science project that trains volunteers to look for seasonal changes in eight specific species in their old growth forest, including red maple. “Most people don’t think of red maple as a flowering tree,” said Forrest, but “its flowers are quite beautiful … this year we saw red maple flowering basically a week earlier than we’ve ever seen it.”

An analysis by Climate Central of recent temperature data showed that winter and spring are the fastest warming seasons for the majority of the U.S., including the East, pushing the rhythm of the natural world further out of kilter. A 2013 study from Duke University said that this specific event—an exceptionally warm late-winter and early-spring—had the strongest effect on plants’ timing than at any other time of the year.

Dave Epstein, a New England based meteorologist and avid gardener, told me that this year, insect behavior is out of whack, too. Garden pests, like moths, are emerging earlier. In extreme cases, as the climate continues to warm, my Slate colleague Rachel Gross explains that “we could lose the link between plants and their pollinators, which could have devastating affects on agriculture.”

This year is also probably a bit of an outlier. Over the past several years, winter has indeed been getting warmer due to human-caused climate change, but “the El Niño has pushed that into overdrive,” Epstein says.

So, yes, this year is weird. And we’ve been having a lot of weird years lately. But one thing’s for sure—don’t take your climate angst out on the gorgeous cherry blossoms.

Eric Holthaus is a meteorologist and a contributing writer at Grist. Follow him on Twitter.