I haven't really followed this issue closely, but I will refer you to a pertinent paper:
Weaver, C.P., and V. Ramanathan, 1995: Deductions from a simple climate model: Factors governing surface temperature and atmospheric thermal structure. J. Geophys. Res. 100, 11,585-11,591 http://www.agu.org/journals/jd/jd9506/95JD00770.pdf It's pretty dense. In fact it describes an entire analytic infrared radiative transfer model. One of the points they address is that the infrared absorption bands of the greenhouse gases have "windows" - regions of the infrared spectrum where the atmosphere remains largely transparent (at least for non-cloudy skies). For Earth, a broad window is present between 8 and 12 microns. One consequence of the window is the fact that even for a warming surface and atmosphere, infrared radiation is still permitted to escape to space through the window. This property puts a limit on the total amount of warming for increasing CO2 and water vapor, that is the windows save us from a runaway greenhouse scenario. This was apparently understood as long ago as the 1920's according to the references in Weaver and Ramanathan. However, they note that the window may "close" slightly as the atmosphere warms and the water vapor amount increases. This occurs because of a process known as "pressure broadening", which means that IR absorption by water vapor at the edges of the window will increase as CO2 and temperature increases. They note that the final amount of equilibrium warming for a given amount of global warming depends on how much the pressure broadening of water vapor absorption closes the window, but I don't think there is concern that the window will completely close. Another issue, which I don't think Weaver and Ramanathan address is that IR absorption by clouds blocks the window. So the total amount of warming for a given increase in CO2 will also depend on how much a change in cloud cover (particularly high/thin clouds) increases IR absorption by clouds. But a runaway scenario based on clouds would require a much larger increase in cloud cover than is expected. In fact, I believe many models predict a decrease in cloud cover. -Eric On Feb 15, 9:06 am, Tom Adams <[EMAIL PROTECTED]> wrote: > One could make an argument that the most troubling potential effect of > global warming is not sea level-rise or drought. The most toubling > potential effect of global warming is *more global warming*. > > Yet there seems to be little public awareness of this. The public > seems view global warming as a problem that can be dealt with later, > but this might not be true. > > "Greenpeace International polled 400 climate scientists during > December 1991 and January '92. The sample included all scientists > involved in the 1990 study of the Intergovernmental Panel on Climate > Change, and others who have published on issues relevant to climate > change in `Science' or `Nature' during 1991. Scientists were asked > whether they thought there would be a point of no return at some time > in the future, if emissions continued at their present rate. By the > end of January 1992, 113 had replied, in the following way: probably - > 15 (13%), possibly - 36 (32%), probably not - 53 (47%). In other > words, 45% believe the runaway greenhouse effect to be possible. " > > http://archive.greenpeace.org/climate/database/records/zgpz0638.html > > "Runaway global warming" (RGW) is the best term I have found for this > (based on googling). Is there a better term? > > What is the status of RGW in the scientific community these days? It > is frige alarmist or mainstream? > > Is there any research that might sort out RGW, determine if its a real > probability, put a probability on it? > > What are the time frames for RGW? Perhaps it would play out over such > long time frames that it would not scare the public into action even > if the mainstream of scientists considered it probable. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
