[pgrote]

I do not know. I am ignorant of the means in which NASA gathers temperature from the middle of the ocean and presume it is satellite. If that is the case, how was the temperature in the middle of the ocean ascertained in 1880? I would presume they base it on datapoints collected using thermometers by those at sea.

[bjwbell]

In 1880 via ship measurements. They'd take out a bucket of sea water and measure the temperature. They still use buoys as part of the sea surface temperature measurement.