Blue - why do you do this to yourself? 1960'S...HONESTLY -
https://www.carbonbrief.org/scientists- ... he%201830s.
Greenhouse gases have been warming the oceans since early 1800's. Pre-industrial and then increases from around 1830 Industrial era.
'The study, published in the journal Nature, draws on a new record of tropical sea surface temperature dating back to 1500, captured in fossilised corals and tiny marine organisms.'
Oceans are important for understanding global climate because more than 90% of the heat reaching Earth’s surface ends up there. Changes in how much heat the oceans take up is one reason why we see periods of faster and slower temperature change throughout Earth’s history.