The Science Behind Fall Leaves
Oct. 10, 2025
Robin Oliverio, Ph.D.
“The falling leaves drift by the window,
The autumn leaves of red and gold.”
-Autumn Leaves, Jaques Prévert and John Mercer
Fall in Western Pennsylvania is a fantastic season – the crisp air, colorful hillsides, and nostalgic TV shows make for a cozy time filled with warm drinks and thick blankets. A large part of that seasonal magic stems from the vibrant color in the trees that line our streets, parks, and rivers. As the weather cools, we start to see red, orange, and yellow leaves floating down to the ground and scattering across sidewalks.
The Science Behind Leaf Color
There’s quite a bit of science behind the art of nature. Leaves appear green because of pigments called chlorophyll 
. These pigments are housed in chloroplasts , which power photosynthesis (the conversion of light into chemical energy). Chlorophyll plays a vital role in photosynthesis, capturing red and blue wavelengths of light to essentially turn sunlight into plant food. These pigments reflect green wavelengths of light, and that is the color that we end up seeing.
During the warmer months, chlorophyll breaks down and is replaced, keeping leaves green. Then, as we move from summer to fall, temperatures gradually drop, giving the classic nip in the air that we associate with fall. In deciduous trees, these cooler conditions signal the trees to start conserving energy for when there will be less sunlight. In this process, , and the underlying brown, red, and yellow colors of the leaves take center stage as the chlorophyll that is producing the green color degrades.
How Weather Impacts Fall Colors
Climate impacts the vibrancy and pace at which the leaves change color. For example, after a dry summer like the one we had this year, experts predict that the seasonal shift will be short-lived . This is because dry conditions impact photosynthesis . Lack of precipitation triggers an earlier end to chlorophyll production , which then affects the intensity of the color we end up seeing.
Stay Updated on Pittsburgh’s Fall Foliage
If you want to stay in the know about the fall colors this season, the Pennsylvania Department of Conservation and Natural Resources releases a weekly foliage report that will give you the most up-to-date details. As our season finally begins to shift into cooler weather, you can follow along and pay attention to how science plays out in the leaves around you.
About Robin Oliverio, Ph.D.
Robin holds a Ph.D. in neuroscience and is passionate about bridging the gap between science and policy. She focuses on using research to inform evidence-based policies that drive positive societal change. She is strongly committed to projects that make a meaningful difference in people’s lives, and she thrives in roles where science meets advocacy, communication, and impact.
If you have any questions or would like a particular topic to be featured, please reach out to Dr. Oliverio, science communications & media specialist, at OliverioR@CarnegieScienceCenter.org