On 30/05/07, Michael Tobis <[EMAIL PROTECTED]> wrote: > > If you've had some calculus, you may remember that some infinite > series converge and some don't. (It's really not a series in this > case but it has some of the same flavor.)
It can easily be analyzed into a series of steps though where the number of steps is infinite, at least in the case of the simpler models. I took Gavin Schmidt's explanation of the simple model he provided over at Real Climate then turned in into a spreadsheet - positive feedback between the ground and the atmosphere with thermal radiation lost to space - from both the ground and the atmosphere. Takes around fifty steps before the feedback becomes unnoticable - no longer showing a change at the eighth decimal place, depending. The spreadsheet is here: http://www.editgrid.com/user/timothychase/Greenhouse It includes a link to Gavin's article. It can be exported to Excel. > Conceptually if each boost around the cycle is smaller than the one > before it, it is possible to have a finite total boost. The > configuration of a planet such as ours, with a stable ocean, is such > that the runaway doesn't happen. The runaway case probably did happen > exactly as you describe on Venus; the difference is that the solar > constant there is higher so it works out differently, so the ocean > boils, the temperature stays very high, and life never arises on that > world to ask such subtle questions. But presumably CO2 had very little to do with getting the greenhouse going on Venus, at least initially. With greater watts per square meter from a brighter, earlier sun (about 15% more than what this planet has ever experienced), water oceans would have gradually evaporated, producing water vapor which acted as a greenhouse gas, much like it does here on earth. The higher the temperature, the more water vapor would have been produced, but this would have also increased the air pressure, raising the temperature at which water boils. It would have been approximately 675 C at over 80 atmospheres when the oceans themselves reached the boiling point, rapidly turning what was left into vapor. At full blast carbonaceous rocks were turned to gas, releasing carbon dioxide. At the high altitudes the water vapor disassociated with hydrogen leaking to space and oxygen reacting with what was left. And yes, this sort of thing is quite impossible here, from what I understand. Convection is one of the processes which keeps the feedback in check. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
