The spring of 2012 shattered almost every imaginable record for warmth in the U.S. Trees bloomed and buds burst weeks ahead of schedule. Now scientists who study plant stages and their relationship to climate say it was the earliest spring on record.

In their study, The False Spring of 2012 – Earliest in North American Record, researchers sponsored by the U.S. Geological Survey analyzed indices of the relationship between temperature and the leaf-out and flowering dates of different plants species. These so-called “spring indices” revealed the spring of last year occurred earliest on record dating back to 1900.

“Much of the central and eastern parts of the domain experienced spring onset as much as 20 or 30 days ahead of their climatological expectations,” says the study, published in the journal Eos of the American Geophysical Union.

Left- Time series of first leaf date index compared to 1981-2010 average. Right-  First leaf date  index differences from 1981-2010 average in 2012 (Eos AGU)

The warm weather arrived so prematurely that the scientists termed it a “false” spring. False, because vegetation emerged from dormancy so soon that it became vulnerable to frost and drought down the road.

“Unusually early blooming in fruiting trees (e.g., cherries, apples, peaches, and pears) was followed by a damaging but climatically normal hard freeze in April,” the study reports.

The Upper Midwest and Great Lakes regions were hardest hit by the April freeze. The study notes that frost damage reached half a billion dollars in Michigan, prompting the federal government to declare the state a disaster area.

Ongoing climate warming raises concerns about an increase in frequency of these false springs the study says:

As global climate warms, increasingly warmer springs may combine with the random climatological occurrence of advective freezes, which result from cold air moving from one region to another, to dramatically increase the future risk of false springs, with profound ecological and economic consequences.

Scientists have already observed certain plant species blooming earlier.

A U.S. EPA report on climate change indicators says that in the Lower 48 first leaf growth in lilacs and honeysuckles are now occurring a few days earlier than in the early 1900s. The most apparent change towards earlier dates in these species commenced in the 1980s the report says.

Although the long-term trend is towards warmer and earlier springs, increasing the likelihood of an event like last year’s false spring, the current spring is cooler than normal – showing there is a great deal of year-to-year variability in the season’s character.


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