It is widely realized that WWii saw changes in the construction of sampling buckets
for sea surface temperature measurement, and many navies switching to water intake temperatures in compiling data from ships at sea.
There is a recognised bias in the dataset from the period around WWII associated with changes in the nationality of the shipping fleets
taking sea surface temperature measurements - the main contributor to the temperature record - due to the war.
Carbon Brief produced a raw global temperature record using using unadjusted
ICOADS sea surface temperature measurements gridded by the UK Hadley Centre and raw land temperature measurements assembled by NOAA in version 4 of the Global Historical Climatological Network (GHCN).
Not only that, but there is increasingly compelling evidence that the recent short - term slowdown in the surface temperature record was much less pronounced than previously estimated, if rapid Arctic warming is fully reflected, along with potential biases from the changing mix
of sea surface temperature measurement sources in recent years.
Global average temperature The mean surface temperature of the Earth measured from three main sources: satellites, monthly readings from a network of over 3,000 surface temperature observation stations and
sea surface temperature measurements taken mainly from the fleet of merchant ships, naval ships and data buoys.