|International Comprehensive Ocean-Atmosphere Dataset|
An dataset maintained by NCAR and NOAA that is used by the three key surface average-temperature histories (HadCRUT, NCDC, and GISS) to calculate sea-surface temperatures.
For more detailed information about how the dataset, click here.
Example Usages -
1. "Oceanic data are based on sea surface temperature (SST) rather than marine air temperature (MAT). All three global products rely on SST series derived from the ICOADS archive, though the Hadley Centre switched to a real time network source after 1998, which may have caused a jump in that series. ICOADS observations were primarily obtained from ships that voluntarily monitored SST."
(Source: Ross McKitrick | , A Critical Review of Global Surface Temperature Data Products )