紅葉はなぜ赤や黄色になるのか｜黄色は夏から隠れていた

Why Do Leaves Change Color in Autumn?

Every autumn, many trees change from green to yellow, orange, and red.

Why does this happen?

In spring and summer, leaves work like little food factories for the tree.

They use the energy of sunlight to make sugar from water and carbon dioxide.

To do this, leaves need a green material called chlorophyll.

There is so much chlorophyll that the leaves look green.

But leaves also have yellow and orange colors inside them.

These colors are there all summer, but the strong green hides them.

In autumn, the days get shorter and the air gets cooler.

The leaves stop making food, and the chlorophyll breaks down.

When the green goes away, the hidden yellow and orange can finally be seen.

Red is different.

Red colors are not waiting inside the leaf all summer.

Many trees start to make them near the end of summer.

Bright, cool days and chilly nights that are not freezing help make the brightest reds.

But why does a tree make a new color for leaves that will soon fall?

Scientists are still not sure.

One idea is that red works like sunscreen for the leaf.

It may protect the leaf while the tree takes useful things back from it.

Another idea is that red is a warning to small insects: "Stay away from me."

So the next time you see autumn leaves, remember this.

The yellow was there all along, but the red is brand-new.