[organsnyder]

How did the ocean stay cool before steamships were invented?

[eptcyka]

There was less CO2 in the atmosphere, which increased its capacity to cool off the oceans.

[Kuinox]

There was less CO2 in the air.

[samatman]

We don't know that they did. It takes satellites to get a representative measure of ocean temperatures worldwide. There's some noisy data from ships dipping mercury thermometers into the oceans, but this was hardly a widespread practice.

[energybored11]

They did not.