The quality of this dataset has been approved by Bruce T. T. Calvert on February 19, 2024. This dataset is a further derived product (classifying as a level 4 data processing level) derived from various source datasets, including sea ice coverage of HadISST2, land mask data of OSTIAv2, the surface temperature climatology of Jones et al. (1999), the sea surface temperature climatology of HadSST3, and surface elevation data of GMTED2010. Sensitivity tests of HadCRU_MLE_v1.2 use alternate sea ice source datasets (COBE-SST2, G10010v2, and G02202v4). These source datasets either have had extensive quality control or are themselves further derived products based on source datasets that have had extensive quality control.