The Anthropogenic Global Warming (AGW) cult is dead wrong about CO2 driving our climate and the graph below reveals their mistake.
The top portion of the graph shows the electromagnetic radiation that is both downgoing (from the Sun shown in red) and upgoing (radiated from the Earth to space shown in blue). All objects that have a temperature above absolute zero (0° K) will radiate electromagnetic radiation at various wavelengths and intensity according to Planck’s law and the center of that distribution will be at a wavelength characterized by the Wein’s displacement law. So our Sun, which has a much higher temperature than Earth will radiate energy at a peak frequency of about 0.5 µm and the Earth will radiate its energy at a peak of about 14 µm.
Much of the downgoing and upgoing radiation is absorbed in our atmosphere and the portion of the graph just below the spectral intensity shows where these wavelengths are absorbed. Fortunately for Humans, much of the UV, X-Rays and Gamma Rays of the downgoing radiation are absorbed in our atmosphere (those wavelengths that are small and are not even shown on the left hand of the chart) and for that reason we exist today. Since light in the visible range of the Sun’s spectrum are allowed to pass through the atmosphere, we have eyes that have evolved to absorb these wavelengths. Organisms that had eyes that see only in X-Rays would be ‘blind’ on Earth and would not have had much success catching food.
Now let’s focus on the upgoing radiation because it is from this radiation that our Earth’s greenhouse effect happens. The Earth would be a much colder place if we didn’t have an atmosphere to trap a portion of the radiating heat from going to space. From an article at American Thinker that explains the Greenhouse effect:
“The Greenhouse Effect is real and necessary for life on Earth. Without it, our world would be a frozen ball that would not be hospitable for life as we know it. The harmful stuff (x-rays and gamma rays) is filtered out, but the light in the visible spectrum enters, and that light energy warms our Earth. The land and sea then respond to that warming energy by emitting light in the spectrum of the infrared (IR), and that energy takes the form of small packets of energy called photons. When those IR photons reach the atmosphere, some of them get absorbed by certain molecules, and that absorbed energy is transferred into the elements of the molecules. That energy causes the molecules to vibrate and heat the atmosphere, and finally, the atmosphere transfers some of that energy back to the Earth’s surface. Again, this is necessary, because if we didn’t have this blocking of IR wavelengths, our average temperatures on Earth would be about 32 degrees Celsius cooler (-18° C instead of the current 14° C). One of the greenhouse gases (GHG) that reflects these IR wavelengths is CO2, but there are others, such as water vapor, ozone (O3), methane (CH4), and CFCs.”
Now here is the portion of the graph that causes so much heartburn with the AGW cult. Looking at the bottom portion of the graph and focusing on the line labeled “Carbon Dioxide”, you can see that the wavelengths of upgoing radiation that CO2 absorbs (which is centered around 14 µm) are positioned of the right hand side of the upgoing radiation curve (which is centered around 11 µm) so CO2 isn’t seeing the higher intensity radiation that gets passed to space. The graph shows that CO2 does a very thorough job of absorbing some of this upgoing radiation (CO2 absorption is pegged at 100% at these wavelengths) and what radiation CO2 doesn’t absorb, Water Vapor takes care of the rest. Adding more CO2 to the atmosphere will not change its absorption spectrum and as this graph shows, there is no more upgoing radiation that it can absorb. In other words, CO2’s radiation absorbing duties are already performing at their maximum level so CO2 is at a saturated state right now with regard to upgoing radiation absorption.
And here is another subtle fact that further shoots holes in the AGW meme. If the Earth were to get warmer then the upgoing radiation distribution would shift to the LEFT (per Wein’s displacement law). That would mean the intensity of the upgoing radiation wavelengths that CO2 thoroughly absorbs would be LESS so the greenhouse warming contribution of CO2 for a warmer Earth would be less than a cooler Earth. Conversely if the Earth were to get cooler (i.e. a little ice age) then CO2 would be a stabilizing factor since the upgoing radiation curve would shift RIGHT and there would be more photons for this molecule to absorb and help bring Earth back into a warmer climate.
CO2’s contributing factor to the greenhouse effect is saturated and even if the Earth warms, CO2’s role in the greenhouse effect will only diminish. That is a hard pill for the AGW cult to swallow.