Radiative Forcing

On Page 28 of the March 2, 2015 issue of Chemical Engineering News, SR has a Concentrate entitled "CO2'S Climatic Impact Measured". SR says "Spectroscopic measurements of Earth's atmosphere have provided the first directly observed evidence that rising levels of atmospheric carbon dioxide are altering Earth's surface energy balance, a parameter known as radiative forcing." It is also said that Earth's total radiative forcing in the atmosphere is currently about 2.3 W per square meter of which CO2's contribution stands at about 1.8 W per square meter.
I thought we might take a closer look at what SR and his references mean and how they come to their conclusion.
Since the writing includes terms with which we may not be familiar, let's take a look at a few of these. Most of us know what "CO2" and "climate" are, so let us start with "spectroscopic measurements ".
Spectroscopy is a study of the light emitted by an object. That light could be generated internally, as for example from a lightbulb or flashlight. It could also be light that is reflected from an outside source, as for example, we can see a person in daylight, because he is lighted up by sunlight. In both cases, what we see is kind of an average of many components of light. There are also some components of flight that we can't see, such as ultraviolet.
However, there is a device which contains a glass prism, such as old Isaac Newton used in his studies of light. It separates the components of light into different bands some of which we can see. It is called a spectroscope. For example, if we have a flame and put some table salt in the flame, we can see through the spectroscope various bands which are characteristic of sodium.
With the spectroscope, we can look at the sun or the stars, and from the presence of the bands we see in the spectroscope and known characteristic bands of various elements, we can determine what the sun and stars are made of. In addition, depending upon the intensity of the bands, we can get some good idea about the concentration of each of those elements.
Just for completeness, we can also shine a light on various samples of matter and look at the reflected light through the spectroscope to see the various bands characteristic of that particular material. As added versatility, the light.
we shine on the sample can be a wavelength of visible light, such as yellow, or invisible ultraviolet light, infrared, or x-rays. In each case, we get back a different picture from the sample. From those pictures, we can usually identify various component parts of the sample and concentrations thereof. For example a sample of stainless steel will show we have iron, chromium, molybdenum, vanadium, etc., with an indication of just how much of each component is there.
The bottom line is that spectroscopy will tell us a lot about composition of matter, with respect to what the components are and the concentrations of each. If we use it on the Earth's atmosphere, we can determine the carbon dioxide is present and it's concentration in the atmosphere. I don't see how it could tell us how "rising levels of atmospheric carbon dioxide are altering Earth's surface energy balance", but perhaps I'm missing something. If I am not, many people are taking a long stretch.
Let's go on to "radiative forcing".
Massachusetts Institute of Technology publishes a newsletter. In 2010, David Chandler said, "The concept of radiative forcing is fairly straightforward. Energy is constantly flowing into the atmosphere in the form of sunlight that always shines on half of the Earth’s surface. Some of this sunlight (about 30 percent) is reflected back to space and the rest is absorbed by the planet. And like any warm object sitting in cold surroundings — and space is a very cold place — some energy is always radiating back out into space as invisible infrared light. Subtract the energy flowing out from the energy flowing in, and if the number is anything other than zero, there has to be some warming or cooling going on."
He also gives the following example: "It’s as if you have a kettle full of water, which is at room temperature. That means everything is at equilibrium, and nothing will change except as small random variations. But light a fire under that kettle, and suddenly there will be more energy flowing into that water than radiating out, and the water is going to start getting hotter. In short, radiative forcing is a direct measure of the amount that the Earth’s energy budget is out of balance."
Notice that Chandler in his example of the kettle did not use the obvious second part, which was when you take the heat source away, the water in the kettle cools. That would've been consistent with his first statement which was that radiative forcing is the difference between energy going in and energy going out.
Notice also that he had nothing to say about why some substances, such as carbon dioxide are claimed to have strong radiative forcing characteristics even at low concentration as compared to many other gasses, such as nitrogen and oxygen.
But going back to the C and E News article, it is all of a sudden claiming that the Earth's total atmospheric radiative forcing is 2.3 W per square meter with CO2 accounting for about 1.8 W per square meter of the total.
That seems to me to be an awful big leap of faith, when in the first place I can't put any energy terms on the reported spectroscopic measurement, nor can I see how carbon dioxide is suddenly a strong radiative forcing component of the atmosphere, whereas other atmospheric major gases are not.