We Finally Know Why Spring Now Shows Up A Week Early In Cities

We Finally Know Why Spring Now Shows Up A Week Early In Cities

Something weird is happening to spring. It’s starting earlier and earlier — but not everywhere. The shift is limited to cities and heavily-populated areas.

Cherry Blossoms in DC (Image: Andrew Bossi)

Late last year, a research study suggested that the spring season’s start was creeping slowly forward so that, by 2100, spring would begin almost a full month earlier than it does today. Now, a new study from researchers at the University of Exeter in Proceedings of the Royal Society B concludes that spring’s start has already shifted forward by a full week — but only in heavily-populated areas. The Exeter team believes the cause is light pollution at night.

The researchers used a combination of ground observations of the dates when the trees first began to bud and satellite data showing light pollution at night. In areas heavily lit up by street lamps and neon signs, the trees were in bud on average 7.5 days early. But the onset of spring in the darker countryside, even in adjoining areas, was unchanged.

The shifting season is also potentially catastrophic to the delicate relationships between plants and animals. Lead author Richard Ffrench-Constant, described the “cascading effects” of the change, which could drastically change which species will or won’t thrive.

“Winter moth caterpillars need to hatch out of their eggs when the oak leaves are fresh and tender and lacking in tannins,” he told Gizmodo. “If the oak bursts one week early then the caterpillars will hatch to find tough tannin filled leaves. Less caterpillars means less food for song birds which also time their eggs to hatch at peak caterpillar densities. So it’s the mismatch between bud burst and insect hatching that causes the knock-on effect on the birds.”

Now that researchers have identified the link between light pollution and seasonal shifts, they intend to pass along the data to cities. Perhaps with a little less light from the ground, spring will stay right where it is.