Does Carbon Dioxide cause climate change?

Carbon dioxide is a minor player in any further warming. It is uniformly distributed in the atmosphere but only absorbs infrared (heat) in a very narrow wavelength range. The CO₂ wavelength range is outside the range of most of the solar radiance that penetrates our atmosphere. It falls roughly inside the wavelength range of temperatures re-radiated when solar radiation heats the earth’s surface. The atmospheric CO₂ already absorbs almost all of the radiation that it can in that range. Most of the warming effect of CO₂ has already occurred in the past and is one of the reasons our planet is not a frozen wasteland. Any increase in CO₂ will have a very minor effect. With CO₂ absorption near saturation, almost all of the re-radiated heat in that wavelength range is already being trapped, so it can have little or no effect on future increases in temperature or supposed forcing of water vapor. With CO₂ essentially eliminated as a source, any increases in temperature must be from some other source.

Source:  This figure was created by Robert A. Rohde from published data and is part of the Global Warming Art project. ‎ The image is on Wikipedia at https://en.wikipedia.org/wiki/User:Dragons_flight/Images#/media/File:Atmospheric_Transmission.png

This figure requires a bit of explaining. The top spectrum shows the wavelengths at which the atmosphere transmits light and heat as well as the “black body” idealized curves for no absorption. It is a little misleading because the data is not based on actual solar and earth data. It is based on two experimental heat sources, one centered at 5525 K (5252^o C or 9485^o F), the approximate temperature of solar radiation, and one centered in the range of 210 to 310 K (-63^o C to 36.8^o C or -82^oF to 98^o F), the approximate temperature range of re-radiated heat from the earth. In reality solar radiation power, (Watts/m²/micron), shown in red, is six million times as strong as the power of re-radiated heat from the earth, shown in blue.

The other spectra are absorption^[1] spectra. The top one shows the relative percent absorption by total atmospheric gases at various wavelengths, (note that this spectrum is practically the inverse of the transmission spectrum above it), and the spectra below that show the absorption wavelength ranges of individual atmospheric gases, but not the relative strength of that absorption in reality. As experimental, not real atmospheric, data they can only tell us the wavelength ranges of the absorption, not their relative strengths.

Note that CO₂ absorbs in the 15 micron range^[2], which is within both the range of re-radiated heat and the strong absorption by water vapor, of which the CO₂ peak forms a mere shoulder. This is used to claim forcing of water vapor by CO₂, without regard to the near-saturation level of CO₂. Lesser CO₂ peaks in the 2.7 and 4.3 micron ranges also only contribute in a minor way, the first is completely covered by a water vapor absorption peak and the second forms a shoulder in another water vapor peak. These minor peaks occur in a region where both solar radiation and re-radiation are minimized. Methane and nitrous oxide are also shown to be minor players, having narrow absorption ranges and low concentrations. Note too that ozone blocks most of the ultraviolet light from the sun.

Water is by far the most important greenhouse gas/liquid in the form of vapor, high and low altitude clouds, rain and snow, which both absorb and reflect sunlight and re-radiated heat from the surface. Water vapor is not uniformly distributed in the atmosphere, being concentrated near the earth, but strongly absorbs heat in a wide range of wavelengths. More heat means more water vapor evaporating from the oceans. Sounds pretty scary, doesn’t it? Contrary to what is assumed by climate modelers, who use this to claim forcing by CO₂, the extra vapor doesn’t remain as vapor. It quickly forms low altitude clouds that strongly reflect in-coming sunlight and heat into space. Any re-radiated heat from the surface that may be trapped by clouds is a small fraction compared to the in-coming solar radiation, so blocking solar radiance has a net cooling effect that overwhelms any increases in trapped re-radiation. High altitude clouds tend to trap heat from being re-radiated into space, but have little effect because the increases in cloud cover due to warming are mostly in low altitude clouds.

[1] Transmission and Absorption are inversely related by the formula A = 1/log T.

[2] The horizontal axis is a log scale in microns so that the 1 to 10 range is in units of 1 and the 10 to 70 range is in tens.

NOTE: Republished from July 22, 2015 Post (media link broken and here restored)

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