Credo Reference is a collection of online reference books. It can be browsed and searched like an encyclopedia.
For example, if you search for global warming, you are shown the topic page on climate change (“the now commonly used term, having replaced “global warming”), extracts from many books, a list of related topics (Climate change, Greenhouse gas, Kyoto Protocol, etc.), images, and a mind map.
It might be a good place to start research for your long essay or project.