How Climate Change Has Ruined Groundhog Day

What a silly tradition actually reveals about our changing world.

Jason Cohn/Reuters

Every Feb. 2, a man in Punxsutawney, Pennsylvania, dons a top hat, bow tie, and gloves, and hoists a groundhog up over an adoring crowd. The groundhog, the famous Punxsutawney Phil, then observes his shadow and—the story goes—has a short chat in “Groundhogese” with another top-hatted man, who translates a prognostication for the audience: If Phil saw his shadow, winter will persist for six weeks (as it did last year); if he did not, spring will come early. The affair is rather silly, and it’s meant to be.

Using animal behavior as a bellwether of seasonal change is nonetheless sensible. Long before calendars dictated the first day of spring, humans used observations of the natural world as a reliable seasonal clock. A robin’s song or a budding flower is a great indicator of whether spring has sprung, and paying attention to these cues is vital for hunters, gatherers, and farmers. The timing of hibernating animals, including groundhogs, emerging from winter slumber is one important indicator that the weather has turned, and there’s reason to believe that today’s Groundhog Day traditions have roots in this idea.

Of course it’s absurd to believe that a captive groundhog like Phil would know much about forecasting weather, let alone communicating those predictions to humans. (There are wild groundhogs that hibernate at this time, but the Groundhog Day phenomenon involves a captive animal.) But even Phil’s wild brothers should be forgiven if they’re predictions of late have been off: Climate change is throwing Mother Nature’s biological timepiece out of whack, bringing earlier springs on average.

The trouble is that plants and animals are not all responding to the warmer springs in the same way. “We know that the clock is getting faster, but it’s getting faster at different rates for different groups of animals,” David Inouye, biology professor emeritus with the University of Maryland, told The Daily Beast. “One analogy might be that one group of species is responding to daylight savings and the other one’s not, and so their clocks are no longer synchronized.”

Scientists call this idea phenological mismatch or asynchrony. Phenology is the study of the seasonal timing of animal and plant behavior as it relates to weather and climate. Climate change affects different species in different ways, which results in natural events that used to coincide drifting further apart. This becomes a problem when, say, a hungry herbivore emerges from hibernation before their food sprouts.

Groundhogs are a species of marmot: large squirrels that generally live in burrows and hibernate through the winter. At the Rocky Mountain Research Station in Colorado, scientists have collected data on the timing of natural events for decades, including the hibernation behavior of Punxsutawney Phil’s alpine cousins, the yellow-bellied marmots. In some recent years, migrating robins have arrived in the area while there’s still four feet of snow on the ground, long before the tasty grubs in the soil are accessible. The first glacier lilies are sometimes blooming before the bumblebee queens emerge from their wintry underground lairs to pollinate them. Hummingbirds may soon arrive from Mexico too late to sip nectar from their preferred flowers.

Climate change doesn’t affect all of these species in the same way, because they’re not all listening to the same cues. Birds may pay attention mostly to day length to time their migrations, whereas the flowers they’re counting on at their destination need soil temperatures to be just right before they bloom. Even the bumblebees and the glacier lily bulbs, which both spend the winter underground, will experience change differently because they sleep at different depths under the insulating blanket of snow.

As for the yellow-bellied marmots, they’re emerging from hibernation more than a month earlier than they did just a few decades ago; the late ’90s and early aughts led to a bit of a population boom, since moms and pups took advantage of the longer warm season to grow healthy and fat.

But that boom was short-lived, Kenneth Armitage, professor emeritus at the University of Kansas who has studied climate change impacts on marmots, said. “In a subsequent year we had prolonged snow cover in the spring; about 50 percent of the adults, about 80 percent of the young died during the hibernation season.”

If there’s too much snow too late in the season, marmots cannot emerge from their dens, and they starve to death. Climate change doesn’t simply raise the thermostat, it also contributes to extreme weather events, which could be bad news for Punxsutawney Phil’s cousins in Colorado.

The premise of Groundhog Day as a spring prediction doesn’t have much scientific merit, but the emergence of hibernating animals in February is a clear sign of early spring. Perhaps the story of seeing a shadow served as explanation—if the groundhogs are not out and about, it must be that they attempted to come out but were frightened back into slumber. That would fit with a related superstition, that if the sun came out on Feb. 2, the winter would be long, but if it was cloudy (which tends to correlate with warmer weather) spring would come early.

If Punxsutawney Phil’s predictions miss the mark, it could be in part because the weather has become a little less predictable, and in part because all the cues in the natural world have shifted just a little, and they no longer all point in the same direction.

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“There are some old adages—things like, well, the time to plant corn is when the oak leaves are the size of a squirrel’s ear, or something like that,” Inouye said. “Some of those may not work the way they used to.”