As the relationship between back radiation and concentration of greenhouse gas is logarthmic, technically there is no saturation point as a rise of CO2 from 10% to 20% in the atmosphere still should have the same effect as a rise from 0,00028 to 0,00056 parts per volume, which is what we are talking about.
There is little discussion here and with a pure primary physical model MODTRAN
you can do several runs with doubling CH4 or CO2 and see that the output has a near constant difference with the half values.
I did that here:
to show that CH4 is not nearly as strong as CO2, when looking at comparable concentrations
and on a logarithmic scale:
Y-axis scale is the relative difference with no greenhouse gas in the atmosphere. So no absolute saturation but when values seem rather impossible to get like >0,001 practically you could speak of a saturation point but with a different definition.
So if this little physical exercise is just as solid as the boiling point of water for instance, futile too discus, what then is the Casus Belli?
The question is what doubling CO2 does to the global temperature. Using plain physics on a black body with albedo effect (several older threads here) the Stefan Boltzmann law will bring you to about 0,7 degrees per doubling CO2 as instantaneous effect, however if we add that temperature to the basic temperature the new temperature is around 0,9 degrees and so on, the limit of that effect would be about 1,2 degrees but it takes centuries for this effect to balance and we are still talking about Earth as a black body.
So from the simple basic physics there is not much to get excited about, it's what happens if you turn black body earth into a planet with an atmosphere, water oceans land and a history. There is simply not enough modelling power to understand the thermodynamics of that system and here separates the scientific opinion. The majority, presently in charge for governing the climate, believes that this system puts a positive feedback to that doubling (actually gain, feedback is something different). This has been based previously on a certain hockeystick, and it's now mainly based on highly simplified assumptions about palaeo-climatic observations in the ice cores et al. A minority of these 'warmers' (Hansen Overpeck cs) believe that the observed strong isotope excursions of the ice age and the Palaeocene Eocene Thermal Maximum 55 million years ago, can be projected on present climate and whenever a tipping point is reached, the positive feedback goes out of control and the temperature skyrockets. Obviously this tipping point is near.
But this vision has no consensus as it is believed that the climate has two balance points, cold and warm, we appear to have tipped over to warm after the ice age and another double tipping over has not been proven in palaeo-climate.
Opposing the government is the underground resistance, the partisans, headed by Dick Lindzen cs
. Many of them are meteorologists who simply do not see it happen. They believe that negative gain or feedback factors will limit the double CO2 temperature to below one degree Celsius (Lindzen: 0,5 due to his iris hypothesis) and they have good reasons for that assumption. Not a lot of them are palaeo-climatologists though so if the indications of the past suggest strange illogical things with climate, better recheck those indications.
Now in a theoretical ideal world, we would jointly investigate the true nature of the palaeo-climate phenomena as it is clear to many that a lot of that evidence is enigmatic and is not concurring with the present paradigms. That’s what I try to do. But the real world is a bit harsher. This
is not really an encouragement to do some objective investigations.