Can you expond a bit on this geezer?
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The bottom line is actually not very much, as the direct radiative effect on surface temperature of doubling CO2 concentration in the atmosphere is only about 0.2oC.
The temperature change due to direct radiation effects of CO2 by itself is at maximum only around 0.2oC due to the fact that water vapor absorption of IR overlaps that of CO2 with more than 10 times the concentration of molecules to intercept thermal IR. The net effect on CO2 radiative effect is to reduce it to one third of what CO2 would otherwise be capable of in the absence of water vapor.
http://www.eia.doe.gov/cneaf/alternate/page/environment/appd_d.html
"Carbon dioxide adds 12 percent to radiation trapping, which is less than the contribution from either water vapor or clouds. By itself, however, carbon dioxide is capable of trapping three times as much radiation as it actually does in the Earth's atmosphere. Freidenreich and colleagues[106] have reported the overlap of carbon dioxide and water absorption bands in the infrared region. Given the present composition of the atmosphere, the contribution to the total heating rate in the troposphere is around 5 percent from carbon dioxide and around 95 percent from water vapor."
The direct radiative effect of CO2 without water vapor to get in the way is 5.35*ln(C/Co), and approximately 1/3 that in the presence of water vapor at average atmospheric concentration of H2Oof about ~3600 ppmv for the whole atmosphere from surface to top of troposphere, against 380ppmv of current CO2 concentrations.
Thus a doubling of CO2 would yield 5.35*ln(2) = 3.71 w/m2 Forcing without water vapor and about ~1.2 w/m2 Forcing at the surface from re-emitted downwelling radiation of CO2 decreased by the presence of current average water vapor concentrations.
Some, pre-global warming hype, studies actually indicate downwelling IR due to a CO2 doubling might actually be below 0.55 w/m2 as measured at the surface.
Kiehl, J. T. and V. Ramanathan, 1982: Radiative Heating Due to Increased CO2: The Role of H2O Continuum Absorption in the 12-18 mm Region . J. Atmos. Sci., 39: 2923-2926.
Introduction:
Within the 12-18mm region, both H2O and CO2 absorb and emit radiation giving rise to the so-called "overlap." This study examines the role of this H2O-CO2 overlap in the CO2-climate proble. The H2O absorpotion, within the 12-18mm region, that has been traditionally included in climate models (Manabe and Wetherald, 1980; Ramanathan, 1981) is the line absorption due to the pure rotational band of H2O. In addition to the pure rotaional band, there is very strong "continuum" absorption by H2O in the 12-18 um region (Roberts et al., 1976). The few climate model studies which include the effect of this continuum (e.g., Wang et al., 1976) have not examined its rl in the increased CO2 radiative effects. In order to isolate the overlap effects of various H2O radiation processes in the 12-18mm region, we comput the radiative heating of the surface/troposphere system due to double CO2 with and without the H2O overlap effects.
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[p. 3] We consider three cases in which CO2 is doubled and the changes in longwave fluxes are computed for no overlap between water vapor and CO2. This is achieved by setting the transmissivity of H2O in the 12-18mm region to be equal to 1. In the second case, the H2O overlap due to the rotaional band is included. Finally we include the H2O continuum and calculate the flux changes using both continuum and line transmissivity (for the pure rotation band) described in the previous section. These cases illustrate the most important aspects of the water vapor overlap.
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Table 1. The effect of CO2 increase on the hemispherically
averaged net radiative heating (wm-2). DFTN is the change
in the net outgoing longwave flux (at the tropopause) due to
doubling of CO2; negative values of this quantity denote
heating of the joint surface/troposphere system. DF¯s is the
is the change in the downward longwave flux at the surface.
Case Comments -DFTN DF¯s 1 Without H2O absorption in
12-18 mm region4.69 3.65 2 H2O line absorption 4.18 1.56 3 Line plus continuum absorption 3.99 0.55
But I'm content to just use a number that is in an acceptable range recongnizable by most researchers so will content myself with the ~1.2 w/m2 estimate derived from the NOAA equation taken from, Myhre et al. 1998.
To determine the effects on temperature measurement at the surface from the downwelling back radiation of 2xCO2 (1.2w/m2), the calculation proceeds as follows:
Starting with 288K initial surface temperature @ current atmospheric conditions.
One applies the Stefan-Boltzman relation:
F=sT4
where:
F = total amount of radiation emitted by an object per square meter (Watts m-2)
s is a constant called the Stefan-Boltzman constant = 5.67 x 10-8 Watts m-2 K-4
T is the temperature of the object in K
to determine the total radiative forcing necessary to maintain the atmosphere/surface greenhouse temperature at the current 288oK surface temperature of the earth.
Flux (F288) at the Earth's surface with atmosphere = 5.67*10-8(288oK)4 = 390.08 w/m2
To which we add the increment of 2xCO2 direct radiative forcing at the surface DF = 1.2w/m2 (i.e at the surface where we poor peons live as opposed at tropopause at the top of the atmosphere where their nobody to complain about the -56.5oC deepfreeze.)
F = 390.08 + 1.2 = 391.28 w/m2
And solve for the resultant equilibrium blackbody temperature at the surface for the doubling of CO2 concentration in the atmosphere.
T = (E/s)0.25 = (391.28/5.67*10-8)0.25 = 288.22K
Final step we determine our result in terms of change in temperature (DT) by subtracting our initial state temperature 288K for the resulting increment of temperature do (2 CO2) direct radiative forcing alone enhancing surface temperature.
DT = 288.22-288 = 0.22K