The Global Learning and Observations to Benefit the Environment (GLOBE) Program, sponsored by NASA, hosts historical data sets (1995 to present) made freely available to everyone. GLOBE provides maps, graphs, and data tables to help you visualize and view data sets of interest.
Data sets are available for everything from air temperatures and soil moisture to tree heights and water transparency. Students and teachers are free to download data for use in their own analysis.
Take some time to understand how to access GLOBE data and the various tools by looking at the GLOBE Data User Guide and viewing the GLOBE Data Fundamentals webinar.