Climate Number: Five Days
The Yoshino Cherry Trees that surround the Tidal Basin in Washington, DC were a gift from Mayor Yukio Ozaki of Tokyo City to signify friendship between the United States and Japan. 2012 marks the 100th anniversary of their arrival. The cherry blossoms also signify the arrival of spring. Whereas in many other plant species the annual timing of blooms are sensitive to factors like precipitation and changes in the length of day, the timing of the cherry tree bloom is almost entirely dependent upon temperature. This makes cherry trees an effective climate barometer, as trends in the timing of their blooms follow trends in spring temperatures. In Washington, DC, the trees bloom early during years when March temperatures are warmer than normal and later when they are cooler than normal. While the average peak bloom date is April 4, this year witnessed a peak bloom date of March 20. This early date is part of a 90-year trend of earlier blooms, with a five day advance in the average peak bloom date. During the same period, Washington, DC’s average March temperature rose by 2.3 degrees Fahrenheit. What is happening in Washington, DC is also happening in Japan: since record keeping began there in 1953, the nationwide bloom date has advanced by 4.3 days with the strongest trends happening in cities where a rapid increase in paved surface has led to an increased urban heat island effect.
For comparison: Another important climatic indicator for plants is the growing season, or the length of the period between the last frost in spring and the first frost in fall and winter. Globally, the growing season is 2.3 days longer than it was 40 years ago.
Sources: Chung, U et al. “Predicting the Timing of Cherry Blossoms in Washington, DC and Mid-Atlantic States in Response to Climate Change.” PLoS ONE 6(11): e27439. doi:10.1371/journal.pone.0027439 and Samenow, J. “D.C.’s cherry blossoms have shifted 5 days earlier: what about global warming and the future?” 20 March 2012. Accessed Online 1 April 2012 < http://www.washingtonpost.com/blogs/capital-weather-gang/post/dcs-cherry-blossoms-have-shifted-5-days-earlier-in-last-90-years-what-about-the-future/2012/03/16/gIQARvtTPS_blog.html> and Wallace, Bruce. “Early Blooms: An Inconvenient Truth for Japan.” Los Angeles Times 23 March 2007. Accessed Online 24 March 2007 <http://www.latimes.com/news/printedition/asection/la-fg-cherries23mar23,1,5416851.story>