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parmenides3, on 19 September 2009 - 16:01 , said:
C-Bob:
As I said on another thread, I am leaning towards the idea that the mechanism that is being sought is nothing more than the long-established greenhouse effect - no need to change the basic principles there. The change to AGW theory would be that the greenhouse effect is not significantly altered by small changes in CO2 concentration - rather, the greenhouse effect's basic ability to retain heat, and how it reacts to changes in incoming energy, is sufficient to explain global warming in conjunction with the sun's varying output.
we need to be much clearer about this; 'greenhouse effect' is no more than a (dodgy) name used to provide a convenient analogy to the global climate system. You seem to be suggesting that the system's record of temperature change might be disconnected from the CO2 content - to a greater or lesser degree - if it can be shown that 'heat memory' from the Sun is in some way the cause of changes to the temperature record. But why would this phenomenon suddenly come into being since the 1950's, and not before?
If the system is retaining more heat than it used to, and the rate of retention is increasing, there must be some physical cause. Thermometers measure current conditions (+/- some short-term hysteresis); other than that, there is no 'memory' in the measurement tools, surely?
P
As I said on another thread, I am leaning towards the idea that the mechanism that is being sought is nothing more than the long-established greenhouse effect - no need to change the basic principles there. The change to AGW theory would be that the greenhouse effect is not significantly altered by small changes in CO2 concentration - rather, the greenhouse effect's basic ability to retain heat, and how it reacts to changes in incoming energy, is sufficient to explain global warming in conjunction with the sun's varying output.
we need to be much clearer about this; 'greenhouse effect' is no more than a (dodgy) name used to provide a convenient analogy to the global climate system. You seem to be suggesting that the system's record of temperature change might be disconnected from the CO2 content - to a greater or lesser degree - if it can be shown that 'heat memory' from the Sun is in some way the cause of changes to the temperature record. But why would this phenomenon suddenly come into being since the 1950's, and not before?
If the system is retaining more heat than it used to, and the rate of retention is increasing, there must be some physical cause. Thermometers measure current conditions (+/- some short-term hysteresis); other than that, there is no 'memory' in the measurement tools, surely?
PHi P3,
I shall skip the hysteresis bit, since VP has answered it already and knows far more about it than I do! So, in response to that quoted above...
In this sense I am referring to the "greenhouse effect" as the effect by which the atmosphere helps to maintain a comfortable temperature for life on Earth. It blocks a certain amount of incoming energy, thereby preventing the daytime temperature from soaring to around 120C. It also blocks a certain amount of outgoing energy, thereby preventing the nighttime temperature from plummeting to around -230C. (These figures are the night- and daytime temperatures of the Moon - since the Earth doesn't stay illuminated on one side for as long as the Moon then these extremes may not be reached in the event of there being no atmosphere, but it illustrates the point.)
So, if you like, the greenhouse effect is the term used for the atmosphere's ability to even out the Earth's surface temperature.
We know that the greenhouse effect stops all the energy (heat) from rushing away from the Earth all at once by, if you like, cushioning the release of energy. (There's more to it than that, of course, because the ground absorbs radiation, the oceans absorb radiation and every object on the Earth absorb radiation, in addition to the atmospheric absorption.)
The Stefan-Boltzmann law tells us that as something heats up it radiates more energy, but its temperature at equilibrium will increase as well (since the emissivity does not increase quite as rapidly as the absorptivity).
So, my thinking which led to this Leaky Integrator idea is that if solar activity remains above a certain level then the absorptivity of the Earth increases a bit more than its emissivity, meaning that the Earth will warm even if the Sun's output remains constant until it reaches its new equilibrium.
As I say, the Sun's average output over the past 60 years or so has been higher than any other 60-year period since records began.
As I have said before (though you may have missed it since you've been away, P3) the temperature increase over the last 100 years or so would require the Earth to retain no more than an extra 1/1000th of a degree Celsius every month, which is not a great deal. Temperatures can still give us peaks and troughs as they always would, but those peaks and troughs would all be 1/1000th of a degree per month higher than they would otherwise have been, giving an increasing temperature trend.
CB
P
