The goal of the GloSAT project was to develop, extend and analyse a consistent record of observed global surface temperatures to help scientists better understand how the Earth's climate has changed since the late 18th century. GloSAT developed a temperature record based on in situ air temperature observations over land and ocean. Prior instrumental records of global mean surface temperature change combine air temperature over land and terrestrial ice-covered regions with sea surface temperature readings, typically with start dates around the mid-19th century. GloSAT extends the instrumental global temperature record further back to the late 18th century through use of marine air temperature measurements, combined with improved understanding of measurement uncertainties affecting land and ocean data.