Climate change reshapes fall foliage along the East Coast

Fall foliage across Maine, Vermont, New Hampshire, and New York is entering a season shaped by warming temperatures and increasingly variable weather, scientists say. The timing of peak colors and the brightness of the leaves are being influenced by climate change, even as the underlying chemistry that creates color remains the same.

Leaves change color as temperatures drop and daylight shortens. Chlorophyll breaks down, revealing carotenoids and anthocyanins—the pigments that give leaves their oranges, reds, and yellows. “They're present the whole time,” says Stephanie Spera, a professor at the University of Richmond who is studying shifts in the fall foliage season. “They're just masked by all the chlorophyll.” Not all trees follow the same color script. Aspen trees, and also some other trees, tend to turn yellow, in part because their roots receive extra nitrogen from fungi, reducing the need to pull nutrients from the leaves. “Aspen trees, and also some other trees, get extra nitrogen from fungi in their roots, so they don't need to make such a big effort to recuperate the last nitrogen from their leaf,” Renner said. Maple and oak trees, by contrast, must produce an energy-intensive “sunscreen” to keep leaves on the branches longer, allowing them to absorb more nutrients.

There’s no one-size-fits-all answer for how climate warming will affect leaf coloration. Renner notes that it is not possible to predict across the board how warming will shape the autumn palette. One thing that remains constant is the chemical process behind color; however, the conditions needed to trigger that process can vary. “The maple trees will continue to be red no matter the temperature, because of the underlying chemical ability of the plant to produce this or that color,” Renner said. Yet trees need cold temperatures to produce the vibrant hues people associate with fall.

Fall colors in some regions and some years are pretty dull because the nights weren't cold enough, Spera added. Higher temperatures in the summer and fall can also shift when leaves begin to fall. Without a stronger decline in temperature, “the trees don't have that cue to start shutting down chlorophyll production and shutting down photosynthesis,” Spera said.

In the region of Maine that Spera has been studying, fall foliage has been delayed by almost a day each decade, mostly due to warmer summer temperatures. Rain and drought can also affect the leaves, with too much rain fostering fungus and too little causing drought scorch—the leaves literally crisp off the trees, according to Spera. After a summer of drought and erratic rainfall, experts predict that New England’s famed fall foliage, which brings an estimated $8 billion to local economies, will be “bright, brief and early” this year.

The variability underscores how climate change reshapes a long-running seasonal icon. Researchers emphasize that while the timing and intensity of colors may shift, the fundamental chemistry behind why leaves change color remains, for the most part, unchanged. The outcome, however, will continue to depend on a tree’s species, local climate, and the interplay of temperature, daylight, and moisture as autumn approaches.