Why Do Leaves Change Color In Autumn?

After returning from New England in early fall, I wanted to understand the science behind the changing of the leaves.  Where do those bright orange and red colors come from?  Here's a bit of a basic science lesson

Leaves are nature's food factories.  Plants take in water from the ground through their roots.  They take carbon dioxide from the air.  Plants use sunlight to turn water and carbon dioxide into oxygen and glucose.  So without plants, we would have no oxygen to breathe.  Plants use glucose (sugar) as food for energy and as a building block for growing.  The process by which plants turn water and carbon dioxide into oxygen and sugar is called photosynthesis.  Chlorophyll in the plants help this happen, and also give plants their green color.

As summer ends, the days get shorter and shorter, and the trees know to begin getting ready for winter.  During winter, there is not enough light or water for photosynthesis.  Trees will rest, and live off the food they have stored.  They begin to shut down their food-making factories.  The green chlorophyll disappears from the leaves.  As the green disappears, we begin to see yellow, orange, red and purple colors that we love so much.  The colors are there all the time, but are covered up by the green chlorophyll.  Sunlight and cool nights of autumn cause the leaves to turn the glucose in maple tress into a red color.  The brown color of tress like oaks is made from wastes left in the trees.

When I was on my cruise, and trees had not turned colors the way we anticipated, the locals told us it was because the nights had not been cold enough yet.  Luckily, when we got to Quebec City we had freezing temperatures at night, and saw some beautiful leaves.  Living in California we have few opportunities to see the leaves turning colors.  I was happy to cruise the East Coast, and get an opportunity to see it firsthand.