6.5.1. Factors Affecting Greenhouse Radiative Forcing
A number of basic factors affect the behaviour of different greenhouse gases as forcing agents within the climate system (Shine et al., 1990). First, the absorption strength and wavelength of the absorption in the thermal infrared are of fundamental importance in dictating whether a molecule can be an important greenhouse forcing agent; this effect is modified by the overlap between the absorption bands and those of other gases present in the atmosphere. For example, the natural quantities of CO2 are so large (compared to other trace gases) that the atmosphere is very opaque over short distance at the centre of its 15mm absorption band. The addition of a small amount of gas capable of absorbing at this wavelength has negligible effect on the net radiative flux at the tropopause.
Also the equation:
DF = 6.3 ln (C/C0) [Equation 19]
provided is empiricaly derived from justifying the IPCC models to adjust model outputs to reflect the contaminated surface temperature series, not from the basic physics of CO2 IR absorption characteristics.
Show me a derivation based in an actual controlled experiment backed up by physics not an equation reflecting the average of several incomplete and severly inadequate Global Climate models.
In the latter, particularly note the summary entitled "Radiative Forcing".
IPCC is known as much for what it doesn't say and leaves out than what it does.
1) Natural CO2 levels tend to follow, temperature change, they do not lead temperature. (due to release of CO2 from hydrates & dissolved CO2 in the oceans, increasing biomass, etc.) CO2 is an effect of temperature excursions in the atmosphere not a cause of such.
2) Much higher global temperatures with lower CO2 concentrations have existed in the past. CO2 concentration is poorly correlated with decadal & century changes in the climate.
Merely calling CO2 is a radiative forcing agent in a model does not make it a cause of global temperature change manifested in the physical world.
1) Natural CO2 levels tend to follow, temperature change, they do not lead temperature. (due to release of CO2 from hydrates & dissolved CO2 in the oceans, increasing biomass, etc.) CO2 is an effect of temperature excursions in the atmosphere not a cause of such.
Precisely why it is so difficult to determine the climate response to increasing atmospheric CO2 at the current rate. There are no paleoclimate analogs to this situation. (By the way, I don't know of any significant CO2 hydrates in the ocean, though they can form at depth from injected CO2. Methane hydrates, on the other hand, could be very signifcant.)
2) Much higher global temperatures with lower CO2 concentrations have existed in the past. CO2 concentration is poorly correlated with decadal & century changes in the climate.
Medieval Warm Period, or an earlier and longer epoch?
Merely calling CO2 is a radiative forcing agent in a model does not make it a cause of global temperature change manifested in the physical world.
As I noted earlier, the paleoclimate view of CO2 is a climate "thermostat" (whether or not you like the Gaia viewpoint). CO2 concentrations act to maintain either a warm or cold global climate.