Whose hand would be on the thermostat?

Once the process was complete, a thermostat using bi metallic expansion principles shut off heat to the unit at the appropriate time.

Setting a limit means weighing up the costs and benefits of a world with temperatures at one level, and comparing them with the costs and benefits if we were to turn down the thermostat.

A thermostat attached to the heating element turns off the heating element as needed to prevent overheating the water in the metal tube (overheating would produce only steam in the supply hose), then turns back on when the water cools below a certain threshold.

And by the way, the assumption that we can safely control the Earth's awesomely complex climate system as if it had a thermostat, making the planet not too hot, not too cold, but just right sort of Goldilocks style this is pure fantasy, and it's not coming from the climate scientists.