Wikipedia is a free web-based encyclopedia, with free meaning free to use, free to edit, and free to copy and redistribute. As of March 2004, Wikipedia contained more than 220,000 articles in English, and more than 290,000 articles in 54 other languages (from the obvious -- Spanish, French, Japanese -- to the obscure -- Esperanto, Walloon, Bahasa Indonesia, Occitan, Tamil, Swahili, Tatar, Nauruan, Nahuatl, Soto).

As a starting point, type in your topic in the search box. A search on "environment" produces a page with a wide range of choices and definitions -- from literature to sociology to ecological -- each one linked to more information. A more narrow topic choice, such as climate change, brings up a definition and how it differs from global warming with recommendations to also see historical temperature record. It offers a table of contents including climate change factors (internal factors, natural factors, human factors, anthropogenic greenhouse gases, etc), evaluation of the relative importance of various factors, attribution of climate change over the past century, global warming episodes in the geological, and more.

Following the links of each of these subjects brings even more choices. For example, clicking on human factors, offers an explanation that includes links to a definition of homo sapiens, as well as specifics on the Intergovernmental Panel on Climate Change and carbon cycles. The choices seem endless, requiring a focused interest.