Poets, philosophers, and even regular Joes generally see the first blossoms of spring as a much-anticipated sign of renewal. Now it seems certain factors–some natural, some human-induced–are causing Spring to spring earlier.
Last year, European scientists looked at long-term records of when a large variety of plants bud and flower. They concluded Spring is arriving earlier there.
Unfortunately, no comparably diverse record of blossom dates exists for North America. Only one plant, the lilac (Syringa vulgaris in the western U.S. and Syringa chinensis in the East), has been tracked so closely.
University of Wisconsin-Milwaukee researchers Mark Schwartz and Bernhard Reiter examined the dates of lilac leaf emergence and first bloom between 1959 and 1993 across the United States. They found lilacs are leafing out earlier (5.4 days earlier in a 30-year period) and blooming earlier (by 4.2 days over 30 years). They also found that the last spring frost is happening sooner (by 4.5 days in 30 years). Those trends compare quite nicely with the 6-day advance detected across Europe.
Geographically, Spring is starting sooner in western North America along the Canada-U.S. border, in the Northeast, and in southeastern Canada. Little change was detected in the north-central United States. Only in two sites in the entire network is Spring arriving later: far fewer than random chance would cause over such a large network.
The advanced lilac phenology in the West seems related to higher temperatures there from March through May; in the East, the changes seem to be primarily driven by warmer Aprils. And increasing carbon dioxide levels are no doubt part of the equation.
What might this change mean? If the lilac’s early bloom is any indication, then other plants–including agricultural crops–may enjoy an earlier start and a longer growing season, producing more food to feed the world.
A sign of renewal indeed.
Menzel, A. and Fabian, P., 1999. Growing season extended in Europe. Nature, 397, 659.
Schwartz, M.D. and Bernhard, R.E., 2000. Changes in North American spring. International Journal of Climatology, 20, 929-932.