The Cooperative Children’s Book Center has an incredible bibliography of books on earth and the environment for children and teens.  The books are broken into three categories:

In My World: Loving the Earth

What Happened Here? Environmental Challenges and Change

Taking Action: Planet Pioneers

The categories have items for many different ages with each book given a handy age range to eliminate guess work.  Nicely, each category is broken into fiction and nonfiction.  Even better, the books are from the CCBC Choices lists which means that they are all worth looking at.