On Jan 3, 8:52 am, Igor Samoylenko <[email protected]> wrote: > Hansen mentioned the Venus syndrome in his Bjerknes Lecture he gave at AGU in > December 2008: > > http://www.columbia.edu/~jeh1/2008/AGUBjerknes_20081217.pdf > > What he said is this: ...
In the chapter 10 'Venus syndrome' of his book 'Storms of my Grandchildren', Hansen says similar thing. But, as far as I understand, he does not properly formulate here what is the condition for runaway greenhouse effect, or 'Venus syndrome'. What he shows with good scientific support is that the climate system is more sensitive to radiative forcing (either solar constant or CO2) at both warmer and colder extremes, due to greenhouse effect of water vapor and ice-albedo feedback, respectively. I think this is reasonable. Then he suggests that even CO2 level of 1000 ppm may be dangerous (this corresponds to "10-20 W/m2" in the Bjerknes lecture, I guess), perhaps first triggering such an event like Paleocene-Eocene Thermal Maximum and then Venus-like runaway greenhouse (evaporation of the ocean). But he does not tell how likely will it be, or how confident he is. (This is a complaint a la Stephen Schneider. I know it is a tall order.) As far as I understand, the value 1000 ppm is just an estimate of the maximum level of CO2 in the atmosphere in the Cenozoic era except PETM. I could not grasp why he considers this level is near the runaway situation. So I am tempted not to use Hansen's book as a reliable source about climate change (though it is still a very interesting book). ***** By the way, some attempts to simulate runaway greenhouse condition in GCM are here (information for experts of climate dynamics): Ishiwatari M., Takehiro S.-I., Nakajima K., Hayash Y.-Y., 2002: A numerical study on appearance of the runaway greenhouse state of a three-dimensional gray atmosphere. Journal of Atmospheric Sciences, 59, 3223-3238. DOI:10.1175/1520-0469(2002)059<3223:ANSOAO>2.0.CO;2 Ishiwatari M., Nakajima K., Takehiro S., Hayashi Y.-Y., 2007: Dependence of climate states of gray atmosphere on solar constant: From the runaway greenhouse to the snowball states. J. Geophys. Res., 112, D13120, doi:10.1029/2006JD007368. http://www.agu.org/pubs/crossref/2007/2006JD007368.shtml (subscription needed for full text) Note that their formulation of radiative processes was crude. Probably they wanted to focus in dynamics. Ko-1 M. (Kooiti Masuda) -- 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
