Each of the following three resources contain huge collections of ebooks--including reference encyclopedias, dictionaries, handbooks & other works that provide useful definitions, explanations and overviews relating to your environmental topic.
They also offer you a convenient and efficient way to discover different subject contexts and perspectives that relate to your topic (e.g. philosophical, ethical, sociological, socio-economic aspects).
Depending on your topic focus, you can choose from DePaul's extensive collection of online encyclopedias, handbooks, dictionaries and other reference works covering different aspects of the environment, some of which are linked below (to see a bigger range of environmental reference resources, click HERE):
Use the extremely helpful encyclopedias & other reference sources linked from this page - they're great starting points for your research!
Still can't decide on a topic, & looking for inspiration? Try searching some of the great news sources listed on the 'News & Issues' menu in this research guide.