With the fall arriving, and because this is the way my brain works, I’ve been wondering why I so look forward to the change from summer to autumn every year. Have you ever wondered why maybe you prefer one season over another? There’s something to be said for not over analyzing enjoyment of a thing because reducing it down to the constituent parts saps it of magic, but I’m not worried about that.
I had this moment the other day that crystalized something for me. I was standing on a hill just as the sun was going down. It was the first day that an honest chill had been in the air signaling the change of seasons. The sky was low and flat, a blue-gray that stretched indeterminately before breaking up into bits of fluff somewhere to the west. The pink orange sun had dropped below the clouds squeezing into the space just above the horizon. A cold breeze nipped at face and filled my lungs. That moment, that collection of sensations, felt very much like home. I’ve seen that sky and sun before, felt that breeze, and I loved it. Reflecting on these feelings in subsequent days the only thing missing from that scene, and my jumping off point into a little bit of science, was trees filled with leaves of the most vibrant orange and yellow. That moment is so quintessentially fall and brings me an amount of joy that I can’t really explain (but let’s give a try).
The above narrative dovetails with some research I was doing while thinking about what to write for this piece. I was looking into trees and photosynthesis, but still had this scene in my head and decided to look into why leaves change color in the fall. I had some Idea that the diminishing sunlight affects leaves ability to perform photosynthesis, but that was it. The answer is actually a beautiful metaphor for change and revealing what actually inside, which maybe explains why I love this time of year.
A few basic ideas to explain before getting into how leaves change are chlorophyll/chloroplast and sunlight. Chloroplasts are the organisms in a leaf cell that facilitate photosynthesis by producing chlorophyll. Chlorophyll is a chemical photoreceptor, contained in chloroplasts, that absorbs sunlight and performs photosynthesis to create plant sugar. Over time chlorophyll degrades from the exposure to sunlight, so the chloroplasts are constantly making more. Next, it’s important to understand that the light from the sun is actually a combination of different colors of light. The sun gives off red, orange, yellow, green, blue, indigo, and violet light (all the colors in the rainbow). Each of these different colors travels to earth along a slightly different wavelike path with some of the colors having longer/higher waves than the others, which affects how they interact with different chemicals.
During the summer when the sun is in the sky for a long period of time and the temperatures are high there is plenty of light for chlorophyll to perform photosynthesis. The light provides energy for the process of photosynthesis, chlorophyll absorbs all the different colors of light that except green. The chemical nature of chlorophyll prevents it from absorbing light that travels along the particular wavelike path that green light does. The green light is not absorbed and it reflects off the surface of the leaf and into our eyes, which is why we see leaves as green. As the hours of sunlight decrease and the temperatures begin to drop the chloroplasts stop making chlorophyll and the remaining chlorophyl in the leaf degrades and isn’t replaced. Without the chlorophyl absorbing and reflecting light other aspects of the leaf are revealed.
With chlorophyl gone the carotenoids that have been present in the trees leaves the whole time become visible. Carotenoid is the same chemical that makes carrots orange and it’s present in various amounts in Ash, Birch, Beech, and Maples. The beautiful hues of orange and yellow that we love seeing in the canopy of fall trees are colors that were in the tree the whole time waiting to be revealed. It’s the trees yearly version of metamorphosis where something old is shed and the inner beauty that was there all along is revealed. I know that it’s probably a bit sappy and that I should look for inspiration in metaphors that are less of a stretch, but I this is a narrative that I love. I worry about peoples’ (specifically me) ability to change which is why I always liked butterflies' process of metamorphosis. But now I can go outside look and the trees and remember that we know not yet what we may be.