Science in Context - GCCC Library
You will need a GCCC membership to access this database - but it's totally worth it!
Try Library Webs to find information that will assist you in the discussion section of your chosen topic. Try search terms such as 'climate change', fossil fuels', etc., then use the Advanced Search function to add keywords to narrow your search. In the search results, select those that are tagged Senior School.
The Nitrogen Cycle
This site provides an easy-to-understand explanation of the Nitrogen Cycle, and a number of links to further reading material - bonus!
A more in-depth look at the Nitrogen Cycle, including nitrogen fixation and nitrification.