Visual Demonstration of How H2O Vapor Dominates the GHG Effect

h2o 1

The above graphic is of a “Looking Up” from the surface calculation from MODTRAN. (Source). Note that the Water Vapor Scale is set to 0.00. CO2 is clearly the dominant GHG in the absence of H2O. Note the 89.176 W/ m^2 for all GHGs combined less H2O. Now look at what happens when H2O is added to the mix. Note how the W/m^2 jumps to 369.264 W/m^2.

h2o 2

Now, both of the above graphics are for 400 ppm CO2, about the current level. Let’s take a look at what it looked like Pre-Industrial Era. The CO2 added by man adds 0.94 W/m^2.

h2o 3

Now if we change the setting to looking down from 0.1 km, and compare 270 ppm to 400 ppm CO2, we see that Anthropogenic CO2 results in a 0.00 W/m^2 change in outgoing IR Heat Flux. That is because CO2 absorbs LWIR between 13 to 18µ at a lower level than H2O, but H2O does eventually capture all the LWIR between 13 to 18µ just at a higher altitude. You can test that using the GasCell at SpectralCalc. (Source)

h2o 4

Here is a GasCell for H2O. It basically absorbs most of the 13 to 18µ/Wave Number 666 by about 50 meters.

gas cell 1

Here is the Gas Cell for CO2. It absorbs most by about 30 cm.

gas cell 2

One last chart to clear up some confusion. I often post that -80°C ice will emit LWIR with a peak of 15µ. Here is the chart. The LWIR absorbed by CO2 is consistent with a temperature of -80°C. The point is to highlight how low energy this radiation is relative to the grand scheme. Yes, the W/m^2 matters no matter what the wavelength, but the physical properties of the wavelengths matters as well.

black body 1

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