> That type of runaway is not possible on the earth, because if the
> oceans boiled away the earth would be completely covered in cloud.
> This would raise the albedo from 0.3 to 0.9 and the planet would cool!
I thought William had somewhere stated that even with an atmosphere
out of pure water vapour there could be clear sky areas without
clouds. I cannot find that statement in the group archives so maybe I
mixed things up somehow.
Anyway, is Hansen being misquoted here? Tbe review of his book makes
it sound, as if runaway global warming of the ocean boiling variety is
a certainty, as opposed to a near impossible event.
Let me add a few other thoughts: The oceans are a few km deep. 10m of
water column is a bar. If the oceans were to evaporate, atmospheric
pressure would rise by of the order of a bar for ever 10m of water. At
atmospheric pressure water boils at 100C, at 30 bar it's more like
250C.
I've done some order of magnitude calculations, and, 100m of perfectly
insulated air column can be heated by 200 W/m2 to the surface
temperature of the sun in a few weeks and melting the world's ice
would take a few decades. To get through the first 10 m (doubling
atmospheric pressure and raising world temperature to above 100C)
would also take a few decades under these extreme assumptions (all the
world's insolation going towards evaporating water, the world being
perfectly insulated against heat loss).
So, to get to 100C in 200 years should take a forcing of the order of
50 to 100 W/m2 by my reckoning.
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