It's crazy to think about where this data is coming from. To recover temperatures over such long time periods, samples where taken from over 5,100 trees, 2,300 ocean sediments, 800 boreholes, 351 coral reefs, and 170 ice cores, historical paper records, and more. You can access the raw data at NOAA/NCEI https://www.ncei.noaa.gov/products/paleoclimatology