Why Do the Leaves Change Color When Autumn Comes?

By Janice Yang ’26 • Nov 9, 2025

Fall in love with autumn in these stunning European destinations (© Euronews, 2023).

When summer’s heat begins to fade and cool breezes arrive, trees quietly start their transformation. The lush green leaves that shaded our days slowly turn brilliant shades of red, orange, and yellow. This dazzling transformation draws tourists to forests and parks every autumn — but have you ever wondered why it happens?

Let’s look beneath the surface of those falling leaves and discover the science behind their colors — and how climate change is altering the timing of this beautiful season.

The Science Behind the Color Change

During spring and summer, leaves are busy performing photosynthesis — the process by which plants convert sunlight into energy. This happens thanks to a green pigment called chlorophyll, which gives leaves their color and power to make food.

But as autumn approaches and the days grow shorter, trees begin to prepare for winter. With less sunlight available, photosynthesis slows down and eventually stops. The tree no longer needs as much chlorophyll, so it breaks down the remaining pigment and stores the nutrients for survival through the cold months.

As the green fades, other pigments that were always present in the leaf but hidden by chlorophyll begin to show. This shift in dominance is what paints the world in the warm tones of fall.

Pigments That Paint the Season

Each autumn color has its own chemical artist:

• Carotenoids and xanthophylls create the golden and orange tones we see in ginkgo and birch trees.

• Anthocyanins, produced from sugars left in the leaves, bring out vivid reds and purples — the signature of maple trees.

  
  

As the pigments change, trees also form an abscission layer — a thin barrier between the leaf and the branch that helps the leaf detach easily while conserving water. Once this layer forms, the leaf falls gracefully to the ground, completing the cycle.

How Climate Change Is Rewriting Autumn

In recent years, the timing of fall foliage has begun to shift — a subtle yet striking sign of climate change.Rising global temperatures delay the breakdown of chlorophyll, meaning trees stay green longer and the “peak” of fall color arrives later. In some areas, leaves even drop before turning fully red or yellow, leaving the season duller and shorter than before.

The brilliance of autumn hues also depends on the difference between daytime and nighttime temperatures: wider gaps create more vivid colors. However, with warmer nights and milder days, this contrast is shrinking — and so is the vibrancy of fall.

These changes don’t just affect landscapes; they also impact ecosystems and tourism. For regions that depend on fall travelers, a delayed or muted autumn can mean fewer visitors and economic strain.

A Changing Season, A Changing World

The transformation of leaves each autumn isn’t just a natural spectacle — it’s a reminder of nature’s delicate balance. Every shade of red and gold tells the story of a tree adapting to its environment, and now, of a planet adapting to human change.

As we admire the fleeting colors of fall, we are also called to notice the signs of a warming Earth — and to remember that even the quiet beauty of autumn leaves carries a message worth listening to.