If you're just starting out your research, it's a good idea to consult an encyclopedia to learn and establish context about an environmental problem you're interested in:
AccessScience is an encyclopedia that gives easy-to-read background information about science topics.
You may also want to browse through environmental issues to spark an interest in a particular problem or group:
Gale in Context: Environmental Studies lists several environmental issues, in an easily browsable format. This resource is easy to read and provides an overview of each issue, as well as related news, academic journal articles, and podcasts on topics relating to climate change and the environment.