According to NOAA, this May tied with 2016 for the hottest May on record going back to 1880. The year to date January through May ranks second warmest for that period. Temperatures in the Southeast were one of the few places on earth that had May temperatures below average, and the temperatures in Siberia were especially warm, along with above normal temperatures in most of the ocean basins. You can read the news story at https://www.noaa.gov/news/may-2020-tied-for-hottest-on-record-for-globe and see more details at https://www.ncdc.noaa.gov/sotc/global/202005.
