Global temperature anomaly data come from NOAA's Merged Land
Ocean Global Surface Temperature Analysis (NOAAGlobalTemp), which uses comprehensive data collections of increased
global coverage over land
(Global Historical Climatology
Network-Monthly) and ocean (Extended Reconstructed Sea Surface
Temperature) surfaces. These datasets have data from 1880 to the present. The land and ocean datasets are blended
into a single product to produce the combined global land and ocean temperature anomalies. The available timeseries of
global-scale temperature anomalies are calculated with respect to the 1901-2000 average, while the mapping tool
displays global-scale temperature anomalies with respect to the 1991-2020 base period. For more information on
these anomalies, please visit Global Surface Temperature
Anomalies.