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Posted at 10:53 AM ET, 03/20/2012

D.C.’s cherry blossoms have shifted 5 days earlier: what about global warming and the future?


Time series showing the March average temperature and cherry blossom peak bloom date from 1921 to 2011 in Washington, D.C. (Data from National Park Service, NOAA)
Global warming may cause cherry blossoms to bloom up to a month earlier than today according to a front page story that ran in the Post last week. But is global warming already changing when the cherry blossoms bloom? And how do the historic changes fit in with future projections?

Link: Could cherry blossoms one day be blooming in winter?

I decided to analyze the historic data and plotted both March average temperatures in Washington, D.C. and cherry bloom dates dating back to 1921 (as long as bloom date records have been kept by the National Park Service). The National Park Service’s chief horticulturist Rob DeFeo has said March temperatures are the key predictor of peak bloom dates.

My analysis of temperatures and blooms dates reveals Washington’s average March temperature has warmed 2.3 degrees in the last 90 years and that the cherry blossom peak bloom date has shifted a little more than 5 days earlier (based on simple linear regression).

In other words, real-world data support the overall idea that the D.C.’s March climate is warming and the blossoms’ bloom dates are shifting earlier in response.

What do these historic trends indicate about the future?

If we simply extrapolate my analysis into the future, it would indicate bloom dates would shift another 5 days earlier by around 2100 - from around March 30 to March 25.

If you read the Post front page story, you’d notice this is a much slower shift than in the study discussed.

The study cited in Post story projected trees would bloom 10 days earlier by 2080 (2070-2099) in a mid-range global warming scenario and 29 days earlier in a high-end scenario - or early March.

Study link: Predicting the Timing of Cherry Blossoms in Washington, DC and Mid-Atlantic States in Response to Climate Change

In other words, this study suggests cherry trees will shift earlier 2 to 6 times faster in the future compared to the past (which means the climate would have to warm that much faster as well).

To look at it another way, D.C.’s climate would have to warm 5 to 14 degrees by 2080 for the study’s projections about bloom dates to be achieved (assuming the relationship between temperature and bloom dates stays the same). The study notes “the model [used] predicted considerable acceleration of the peak bloom date in .... cherry trees in the region towards the end of the century.”


From the study “Predicting the Timing of Cherry Blossoms in Washington, DC and Mid-Atlantic States in Response to Climate Change”: Top panel shows peak bloom dates from 1950-2000. Middle three panels (left to right) shows shifts in bloom dates for a mid-range global warming scenario in three time steps. Lower panel (left to right) shows shifts in bloom dates for high-end global warming scenario. View big. (Plosone.org)
I can conclude a few things based on my analysis, existing scientific asssessments of climate change, and the study featured in the Post:

1) There is a clear March long-term warming trend and blossoms have responded by blooming earlier

2) Based on the build-up of heat-trapping greenhouse gases in the atmosphere and the high likelihood for additional warming in the future - per multiple scientific assessments - there is no reason to think the shift towards earlier bloom dates will not continue.

3) The study’s high-end scenario projection for peak bloom dates 29 days early compared to present by 2080 doesn’t seem too plausible. It would require an incredible, six-fold acceleration of the warming trend in the region, and the temperatures presently are warming at a much lower rate. The mid-range scenario - which would require the temperature rate to double - is more plausible, but still out of step with the current temperature trends.

Related link: As Climate Changes, Tidal Basin Cherry Blossoms Could Peak At Their Earliest Yet (Brad Johnson, Think Progress)

Additional cherry blossom reading/photography:

Washington Post Cherry Blossom Festival coverage
Plan your cherry blossom trip
Cherry blossoms bursting out (PHOTOS 2012)
Washington, D.C. cherry blossoms destined for early bloom, Capital Weather Gang prediction
Cherry Blossom timeline: A century of drama and beauty
Washington’s century-old cherry trees: wizened but still able to bust a bloom
Your Cherry Blossom photos (gallery)
Poll: when will the cherry blossoms peak?
Cherry blossoms with an overcast sky (PHOTOS, 2011)
Washington’s cherry blossoms in the snow (PHOTOS, 2011)
A cherry blossom bird’s-eye view (PHOTOS, 2010)
Cherry Blossoms Wind Down as D.C. Greens Up (PHOTOS, 2009)
Cherry Blossom Morning (PHOTOS 2009)
Washington D.C.’s Cherry Blossom Bloom Begins (PHOTOS, 2009)
Photography: Falling Blossoms & Spring Scenes, Kevin Ambrose (2008)
Photography: A Blooming Good Time (2008)
Photography: Glorious Cherry Blossom Sunrise (2008)
Photography: Cherry Blossoms by Night (2008)
Photography: Flying High as Spring Blossoms (2008)

By  |  10:53 AM ET, 03/20/2012

Categories:  Latest, Climate Change, Cherry Blossoms, Local Climate

 
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