Google - good for taking a very wide view of a topic, using a variety of materials not found in library databases (blogs, some news sources, reports, etc.) Domain searching can target your search results example, "climate change" + :.edu | :.org | :.gov.
Google Scholar - still a huge swath of information, but more focused on scholarly publications (including journal articles, book chapters, conference proceedings, etc.)
Web of Science, Scopus, and JSTOR - academic databases with an explicit focus on scholarly publications, with many options for complex, targeted searching
Specialized databases - some are focused on a subject area (EconLit, America: History and Life, etc.), while others are focused on a type of source (news, primary sources, images, videos, etc.)