You may be interested to hear that Prof. Ray Pierrehumbert came to the same conclusion as you, that a boiling away of the oceans was impossible for the same reasons you give, in this paper:
Pierrehumbert, R. T. 1995: Thermostats, Radiator Fins, and the Local Runaway Greenhouse. J. Atmos. Sci. 52, 1784-1806. http://geosci.uchicago.edu/~rtp1/papers/JASRadiatorFins.pdf I think he also deals with Wiiliam's point which I imagine was that clouds only form in rising air, and since what goes up must come down, then only 50% of the surface can have rising air and be covered in clouds. Logical, but not true of Venus! Cheers, Alastair. On Jan 2, 4:29 pm, "[email protected]" <[email protected]> wrote: > > 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. -- You received this message because you are subscribed to the Google Groups Global Change ("globalchange") newsgroup. Global Change is a public, moderated venue for discussion of science, technology, economics and policy dimensions of global environmental change. Posts will be admitted to the list if and only if any moderator finds the submission to be constructive and/or interesting, on topic, and not gratuitously rude. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/globalchange
