Planning trips to witness natural phenomena always involves a degree of uncertainty—after all, nature isn’t known for sticking to a schedule. Colorful fall foliage is no exception. But with a changing climate, the unpredictability of the autumnal season could increase even more.
This is because temperature and precipitation, two of the most crucial factors that affect the timing and vibrancy of fall colors, are both directly influenced by a warming planet. For those anticipating the autumn spectacle, here are three things to know.
Longer summers may delay fall colors
Trees rely on cooling temperatures in the fall as their cue to stop producing chlorophyll, the pigment that gives leaves their green color and allows them to produce food using energy from the sun. When plants stop making chlorophyll, other pigments in leaf tissue get their chance to shine. Those pigments include carotenoids, responsible for the yellow, orange, and brown hues of autumn; and anthocyanins, which yield rich red and purple shades.
Mukund Rao, an ecoclimatologist and carbon cycle scientist at Columbia University’s Lamont-Doherty Earth Observatory, says there are indications that hotter summers are already altering this natural process in parts of North America. Specifically, he has noticed in some recent years, trees have kept their green color a few days longer into the fall than usual. This change in timing has appeared in spots across the northeastern United States, which is home to a slew of popular destinations for viewing fall foliage, including New England and upstate New York.
Rao and other scientists use a network of cameras known as PhenoCams to study changes in the timing of chlorophyll slowdown. This collaborative project, which involves scientific facilities worldwide, uses time-lapse cameras mounted on high vantage points like rooftops and towers to monitor seasonal changes in vegetation, such as the timing of leaf color change, leaf drop, and the emergence of leaves in the spring.
“Because the summers are longer and you have warmer weather later in the year, the leaves remain green longer and the autumn colors show up later,” Rao explains.
Drier summers may affect the vibrancy of fall colors
Summer precipitation plays a significant role in how vibrant fall foliage will be, says Rao. Trees that receive adequate rainfall during the summer produce the necessary amount of sugars in their leaves to put on an eye-popping autumn show.
In areas where climate change leads to summer droughts, the colors may not be as striking.
“In a [hypothetical] year with hot temperatures and little rain, the trees would be pretty stressed,” he says. “And so fall colors in those years would not be very vibrant. The trees would just drop their leaves.”
Shorter leaf-viewing seasons could become the norm
While temperatures dictate when leaves start to change color, it’s the shortening daylight hours as summer wanes that prompt trees to drop their leaves. This part of the process remains unchanged (the planet may be hotter, but the rate at which the Earth orbits the sun is still the same), so the timing of leaf drop remains consistent.
That means that climate change may ultimately cause the peak period for seeing fall colors to shrink.
“The speed at which the transition happens is becoming faster,” says Rao. “You get just a very short period of the orange and red and yellow leaves and then they turn brown and fall off.”
What does this all mean for travelers?
Timing is everything when it comes to planning a fall foliage trip. While that has always been the case, climate change may require travelers to plan even more carefully.
When fall colors emerge later but leaves drop at the usual time, the window for experiencing the autumn display at its most spectacular can potentially grow smaller. So it’s more important than ever to be flexible with your travel dates. Consider recent weather patterns when selecting a destination. In addition, keep up with foliage reports, such as the interactive prediction map recently released by SmokyMountains.com.
