The Science of Fall – Why Do Leaves Change Color?

As summer comes to a close and the temperature outside begins to cool, many deciduous trees around the United States begin to change colors. The once-green leaves begin to shift into dazzling shades of red, orange and yellow. Have you ever wondered why this transformation occurs? It’s simply science – read below to learn more!

A Colorful Chemical Reaction

During the spring and summer months, leaves are responsible for producing the nutrients essential for the tree’s growth through a process known as photosynthesis. As the roots of the tree absorb water and minerals from the soil, and its leaves take in carbon dioxide from the air, a chemical within the leaves themselves called chlorophyll (which give leaves their green color) combines the two, creating glucose and other compounds that the tree feeds on.

By fall, many trees and plants stop producing chlorophyll to conserve energy in preparation for the coming winter. This lack of chlorophyll production allows other pigments within the leaves to show through. These include:

• Xanthophylls, which produce variations of yellow 
   
• Carotenoids, which produce orange hues 
   
• Anthocyanins, which produce shades of red

Because these pigments take longer to break down than chlorophyll, during the warmer months when a tree is continuously undergoing photosynthesis, they remain hidden. External factors including light, temperature and water also affect a leaf’s coloration. According to the UC Davis Arboretum, cooler temperatures help the fall colors shine while warmer weather speeds up the process by causing quicker deterioration of chlorophyll.

Celebrate Fall

While enjoying vibrant fall foliage, we encourage you to continue learning about science in the world around you! Here are a few ideas to kick off your autumn of exploration:

• Take a stroll in your local park as a family to view the changing leaves. How many colors can you spot? 
   
• Head to a nearby apple orchard. Did you know that similar science determines pigments of apple colors too? Find out more! 
   
• Chilly or stormy days don’t have to rain on your fall fun — stay cozy inside with a seasonal book! Which from this list will you pick up from your local library?

Don’t forget! Keep an eye on our blog for more family-friendly STEM trends.