The Fall of Autumn

Autumn is fast approaching here in New England. Every year, I anxiously await the crisp fall air and, of course, a chance to take in the colorful foliage.

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I’m not the only one who looks forward to fall colors. Millions of tourists flock to New England to view the autumn leaf display. These so called “leaf-peepers” generate a huge amount of revenue for the region, but scientists are now discovering that climate change could shift when and to what extent the leaves change their color in the fall.

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Leaf-peepers in New England. Image credit:

Climate change can affect the onset of fall weather and the production of autumn leaf colors. For example, the growing season is now two weeks longer than it was in the beginning of the 20th century. This is due to warmer average temperatures brought on by increased greenhouse gas emissions. But, before we talk about this further, it’s important to understand why the leaves change color in the fall.

Plants produce a pigment called chlorophyll during the spring and summer. The function of chlorophyll is to capture sunlight, which is used for photosynthesis, the process by which plants make their food. The chlorophyll can only absorb red and blue wavelengths of light. So, the green light gets reflected back to your eye, making the leaves appear green. As fall approaches, the leaves start to separate from the branches, cutting off the flow of nutrients to the leaves, which then limits the production of chlorophyll. The chlorophyll that is left in the leaves is broken down by the sun.

Leaves produce other pigments as well, known as carotenoids, which appear yellowish. The abundance of chlorophyll in the leaves masks the carotenoids during the spring and summer. As the chlorophyll disappears in the fall, the yellow carotenoids become more prominent. Leaves that appear red in the fall contain pigments called anthocyanins. Anthocyanins are only produced in the leaves of many trees in autumn, so you don’t see them during the spring and summer. It’s these extra pigments, or mixtures of pigments, that give trees their brilliant fall color.

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A red maple leaf. The green in the leaf is left over chlorophyll, which gets broken down as fall approaches. The red pigment is anythocyanin, which is only produced after the growing season. Image credit:

So, how will the changing climate affect the fall leaf display? Well, the answer remains unclear. The longer growing season could shorten the duration of fall foliage. In addition, hotter temperatures and droughts can cause leaves to fall off the trees earlier. Anthocyanin, the red pigment, is best produced during cold sunny days and, therefore, may be inhibited by increased precipitation associated with climate change in the Northeastern US. However, a recent study  from Harvard University showed that there may be hope for autumn in New England. The study predicts that autumn leaf colors will emerge later, but will actually appear brighter and last longer as climate change progresses.

How will climate change affect fall foliage? Scientists are trying to figure out the answer. Image credit: National Geographic
How will climate change affect fall foliage? Scientists are trying to figure out the answer. Image credit: National Geographic

Although the Harvard study paints a hopeful picture for the future of New England’s autumn foliage, we still don’t really understand how climate change will affect the timing of biological events that occur in the fall season. In fact, a recent review paper pointed out the wealth of scientific studies on the effects of climate change on biological events in the spring and the extreme lack of studies on fall events, such as when leaves change color and drop from the trees. The display of colors in the fall may be further complicated by the migration of plant species in response to warming temperatures. For example, sugar maples are one of several species of trees expected to shift their range to the north as temperatures rise.

Climate change and its related effects are already well underway. Things we take for granted, like the enjoying the beauty of autumn foliage, are going to change in the not-so-distant future. Therefore, we need to understand how to deal with the intensifying effects of climate change. Scientific research can predict what’s to come, but to ensure the future of our planet all of us have to work together to support funding for science and reduce greenhouse gas emissions. Here’s how you can help: UCS EPA

And here are some great places in New England to get out in nature and enjoy the wonders of fall!