A similar scenario is setting up for another devastating frost, on the heels of what is known as a “false spring.” The warmth across much of the Lower 48 states has been exceptional, with most locations in the southern and eastern third of the United States seeing one of their top 10 warmest winters on record to date, as if skipping ahead a season.
The USA National Phenology Network, which tracks the timing of seasonal events in plants and animals, has documented an unusually fast spring arrival based on indexes it uses to gauge the status of tree leaves and flowers.
“Spring leaf out has arrived in the Southeast, over three weeks earlier than a long-term average (1981-2010) in some locations. Charlottesville, VA, is 24 days early, Knoxville, TN is 20 days early, and Nashville, TN is 18 days early,” the network wrote on its website. “In parts of the Southeast, this year’s spring is the earliest in the 39-year record."
The network’s map that tracks the emergence of spring leaves shows they have arrived as far north as the Virginia Tidewater and southern Delmarva.
Theresa Crimmins, director of the network and a research scientist at the University of Arizona, said spring has arrived up to four weeks early in some locations based on several indexes.
“One of the biggest [concerns] is that we’re absolutely not past the risk of frost in a lot of these locations,” she said in an interview. “I’m seeing a lot of reports [of] leaf buds breaking and flowers blooming in a lot of those early-blooming plants. That’s definitely a problem.”
Crimmins explained that trees can bounce back from a frost. “But if flower buds get hit by frost, typically they do not regenerate those buds and then you won’t see fruit,” she said.
In 2017, abnormally warm conditions in February resulted in many species flowering prematurely in the Southeast and Mid-Atlantic. Then a severe frost hit in mid-March. South Carolina lost 85 to 90 percent of its peach crop. In parts of Georgia and North Carolina the blueberry crop was “devastated.” In Washington, about half of the cherry blossoms were damaged.
In 2012 and 2007, there were also so-called false springs. A study published by the American Geophysical Union in 2013 determined the false spring of 2012 was the earliest on record in North America.
“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,” according to the study, published in the journal Eos. “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.”
Rising winter temperatures from human-caused climate change would seem to increase the likelihood of false springs in the future. However, the rising temperatures would also potentially decrease the intensity or even eliminate the occurrence of killer frosts that might follow.
Studies that have analyzed how false springs might change in the future have shown mixed results. The 2013 Eos study projected climate warming would “dramatically increase the future risk of false springs.” But a 2014 study in Geophysical Research Letters indicated “observed decreases in false springs are consistent with a warming climate.” A 2015 study in Environmental Research Letters concluded: “global climate change may have complex and spatially variable effects on spring onset and false springs, making local predictions of change difficult.”
Crimmins encourages citizens to help scientists better understand false springs by joining its Nature’s Notebook citizen science program, by sharing observations of how the seasonality and behavior of plants, flowers and trees, as well as animals, are changing in their backyards.
“Even though really early springs are becoming more frequent, we have a limited understanding of what the full ramifications of that are with respect to ecosystem functioning and implications for invasive species and spread of disease,” she said. “The more information we have, the better we can disentangle the nuances of the relationships.”