https://www.smithsonianmag.com/blogs/national-museum-of-natu....

"The true heavyweights for reconstructing ancient seawater temperatures are the microorganisms. Foraminifera, single-celled organisms roughly the size of the period ending this sentence, occur nearly everywhere in the oceans and have an exquisite fossil record."

We have reasonably accurate sea surface temperature data from 1945 to present, about 78 years. We have less accurate measurements back to the 1880s. Finally, we have proxy records going back thousands of years, based on isotope fractionation ratios and other paleoclimate data.

I located https://www.epa.gov/climate-indicators/climate-change-indica...

Especially Figure 2 on that page, a map showing the change in Sea Surface Temperature, was interesting.

Do you have more information on what changed around 1945? (I mean, I could probably guess. I was wondering if you're looking at different sources than I am.)

On how many points ? The ocean is big, you know.