I admit that I am not an expert in global warming, etc., and it has been a long time since I played with infrared spectrophotometers, but I will add a few comments to your posting. (This is usenet where anyone can post even even they do not know what they are talking about.)
I did a quick check using Google and I found your figure as part of a Wikipedia article: http://en.wikipedia.org/wiki/Sunlight.
I have no reason to doubt the figure. The figure shows the solar irradiance between 250 and 2600 nm. This range seems to cover most of the incoming solar energy. The figure shows that there is only a small effect of CO2 in received sunlight near 2000 nm.
However an important part of the 'greenhouse effect' is that sunlight comes in easily (as through the glass of greenhouse), warms the Earth which then radiates as heat energy in the infrared. If something blocks the infrared from being radiated back to space then the Earth will warm. Thus we need to look at the spectra of infrared light in the range emitted by the Earth.
The wavelength at which peak intensity is determined by lambda = B / T. Where B = 2.8977685 x 10-3 m K. This comes from http://en.wikipedia.org/wiki/Black_body
If we assume that the average temperature of the Earth is 20C or 293K then this gives us 9,890 nm. (I do not actually know the average temperature of the Earth so I just guessed but the value is probably accurate to within 10%.)
The figure that you gave does not cover anywhere near 9,890 nm. A little more Googling gave me this figure: http://www.iitap.iastate.edu/gccourse/forcing/images/image7.gif
Like all data on the internet, I have no way to verify its accuracy. (However since it comes from an Iowa State University web site, I thought that you might give it a little more credence since ISU is reasonably local to you.)
The ISU figure shows major absorption by CO2 at around 2600 and 4000 nm and blocking beyond 13,000 nm. I think that the feature at 4000 nm was the one that I was seeing back when I was playing with infrared spectrophotometers.
The ISU figure indicates that water vapor, CO2, and methane all have effects upon the atmosphere's absorption of infrared and these three are generally listed as the major greenhouse gases. O2 and O3 also have their effects with the mjor feature between 9,000 and 10,000 nm. However I think that most people like the presence of O2 in the atmosphere.
My major reason for responding to Scott Lurndal's posting was his statement that "CO2 is a trace gas amounting to less than one tenth of one percent of the atmosphere." with its implication that such a small amount of the atmosphere could not have a major effect. As my experience with infrared spectrophotometers and the Iowa State University figure indicates, even a small percent of CO2 has major affects in the absorption of infrared by the atmosphere. That small percent of CO2 makes the atmosphere nearly opaque to infrared in certain frequency bands.