> I cited a paper by Pierrehumbert which showed that a boiling away of
> the oceans was not possible because the as the oceans boiled the
> vapour pressure would increase the atmosphereic pressure so raising
> the boiling point of the oceans.
Very strictly speaking there is no boiling. Boiling is the formation
of bubbles of vapour in the water, because the pressure inside the
bubble is bigger than the pressure of the atmosphere. For a kettle
exposed to the open atmosphere, that external pressure stays constant
at 1 atmosphere. The water vapour released has no measurable impact on
the external pressure.
When the whole world warms to 100C, no bubbles with water vapour will
form in the ocean; rather the atmospheric pressure will go up to
around 2 atmospheres.
But that does not mean the water on Earth could not in its entirety
turn into vapour (though strictly speaking again, the 400 bar or so
implied from evaporating 4 km of ocean get us beyond the critical
point for water of 214 bar and 372C beyond which there is no phase
boundary between the liquid and gas phases of water)
> What I am saying is that an abrupt climate change is a runaway event.
> But it need not result in the Earth being in a similar state to
> Venus. It is the term "runaway" which is confusing, and I have been
> told not to use it, but I do because to me it means a positive
> feedback of more than 1.
Just talk about tipping points that result in Earth moving from one
stable equilibrium to another. Then people won't think you are talking
about Earth turning in Venus.
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