EBSCO maintains a thesaurus of keywords to help you make sure that your search is more specific.

For example, if you search DISCOVER for articles with 'global warming' in the title you will find over 2 million results appear.

From your search results list use the All filters button to make the filters menu appear on the right hand side.

Scroll down the Subject section. You'll see a selection of subject terms based on the search you ran. Tick the ones that are relevant to your search and then Apply. You will now have a smaller set of results to consider.