Albedo(clouds & dust),
IR irradiation from surface absorbed in 1st hundred feet of atmosphere where it is predominately dissipated as kinetic energy.
Transport of heat from the surface to the upper atmosphere by convection dominated by
- N2 & H2 kinetic energy &
- water vapor(latent heat of vaporization/sublimation)
released radiant energy to stratosphere and on into space.
downward directed re-radiant IR is absorbed in the upper region of the atmosphere dissappated as kinetic energy not returning to the surface except by convection of cold air.
The role of CO2 is minimal by virtue of the near total absorption of IR in a very short path of troposphere. Adding more CO2 does not increase the capacity of air to absorb more IR at CO2 wavelengths, its just more molecules in the mass, same is true of NH4 & CFC's. Watervapor(latent heat), N2 & O2 kinetic energy are the dominant and overwhealming factors transporting heat from the surface to the statosphere where re-radiative loss becomes the dominant transport to space.
The main reason that I'm responding to this is that your original contention was this:
I find it interesting that out of all the range provided, the GW folks never present or even apparently consider the possibility that global climate temperatures can fall as well as rise. This is a telling note. They appear to be totally dedicated to demonstrating rising global temperture inspite of historical evidence that climates tempertures make excursions downward even with atmospheric CO2 concentrations much higher than even those assumed doublings of IPCC's GCM story lines.
Of all the mechanisms that you propose above, the only one that is capable of producing a significant global cooling is a change in albedo. As we've mentioned Mt. Pinatubo, an additional short-term mechanism is blocking of incoming solar radiation by atmospheric (volcanic, in this case) aerosols.
The significant global cooling mechanisms are those which substantially alter the Earth's radiation budget. Milankovitch forcing is therefore climatically significant because it's directly responsible for changes in the amount of solar insolation. Obviously, if the Sun's energy output was to decrease, that too would result in reduced insolation and therefore cooling. The most-commonly-held explanation for the "Little Ice Age" was a decrease in solar output during the Maunder sunspot minimum, and thus there was no Earth-based cooling mechanism. (I will note from a brief perusal of abstracts of the AGU Spring meeting, where I found the Wentz and Schabel MSU data re-analysis papers, indicates that the Maunder Minimum - LIA cause-effect relationship is not community consensus.)
A lot of people ask about the Ice Age - CO2 relationship. It appears that CO2 acts as a thermostat, but it is not the cause of major warming or cooling trends: insolation is. Once there has been a climatic shift, however, either elevated or reduced atmospheric CO2 concentrations act to maintain either a cold or warm climate, and cause 'resistance' to internal global temperature shifts. This is augmented by oceanic feedbacks, specifically iron input to the ocean via continental dust transport.
As an aside, it's interesting to me that we have different perspectives. My dalliance in geochemistry allowed me to see "beyond" chemistry; climate, specifically paleoclimate, shows the interaction and complexity of Earth's physical processes.
the only one that is capable of producing a significant global cooling is a change in albedo.
You leave out long term solar irradiation changes which do have long term variations as well as the 100kyr orbital precession of muller, (though the latter induces a change in stratospheric cloud cover which is a change in aldebo).
Milankovitch forcing is therefore climatically significant because it's directly responsible for changes in the amount of solar insolation
Actually the theoritical Milankovitch forcing of eccentricty does not fit as well as that of orbital precession. Orbital precession accounts for the 100ky variation much better than Milankovitch, and does not suffer from several inconsistancies that arise under Milankovitch.
Read:
My dalliance in geochemistry allowed me to see "beyond" chemistry; climate, specifically paleoclimate, shows the interaction and complexity of Earth's physical processes.
Anyone who has dabbled in prospecting, fossil collecting and rockhounding has that perspective, that along with astronomy, is what captured my interest in the sciences in my younger years under the influence of my grandfather & uncles.
My perspectives are much broader than the bare bones of what I have stated in this forum, most of which I prefer not to mention, but rather allow papers and substantive articles of others in the academic community to speak for me. It is useless for an internet personality to claim any credential and expect it to mean anything.
The web, I find, is a great leveler where ideas have to stand on their own more than on the personality or credentials of the speaker.