Addressing the World War 2 Warm Anomaly in HadSST.4.2.0.0

ABSTRACT We present an update to the Hadley Centre Sea‐Surface Temperature dataset (HadSST.4.2.0.0) that addresses residual warm bias during the Second World War (WW2). Using an existing quantitative definition of the WW2 warm anomaly we identify Engine Room Intake (ERI) bias corrections as the dominant factor in this warm bias in HadSST4, and use this to propose new constraints on ERI bias estimates prior to 1950. In addition, we implement corrections for truncation bias in observations from the Japanese Kobe Collection, spanning the period from 1933 to 1961. We evaluate the effects of these changes with respect to the previous version of HadSST and compare with the most recent iterations of other SST datasets including ERSSTv6, COBE‐SST3 and DCSST. We show that it is possible to remove the WW2 warm anomaly using a physically‐based approach that maintains the independence of HadSST from land surface temperature records, and preserves structural diversity within the range of available global SST datasets.