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
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:
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
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.
You are at least closer to being an expert than I. I'm not a physicist
and my involvement with solar heating panel development has led me to
focus almost exclusively on inbound energy and those aspects of
absorption, reflection, and re-radiation in that limited (but still
It's the same figure - as I was trying to learn how to /design/ a
super-efficient panel, I collected bits and pieces like this to mark my
path. (Rather like dropping bread crumbs in the forest.)
It appears reasonable. I found several sets of independently produced
measurements on the nasa.gov web site, and a number of similar plots
based on those measurements, which seemed to agree - but I'm ignorant of
how they determined which atmospheric components contributed to the
"notches", since that info was outside of my 'focus'.
Yuppers - in a simplified view, we need to radiate as much back through
the photosphere as passes inward - maintain an equilibrium...
...but I think it's not so perfectly simple for at least two reasons:
First, the planet has a significant internal heat supply which isn't
perfectly insulated by the mantle; and second, the altitude of the
blocking "something" may be significant - and I will be quick to say
that I'm completely ignorant of the quantitative effect of either factor.
Another familiar page (which sent me off to study Planck's work, which
made my head hurt) which provided some valuable clues to designing a
thermal diode that could be produced in a woodshop.
I don't know, too, but can accept it as a starting point.
Proximity doesn't give 'em any edge on credibility, but immediately I'm
interested in how the data was acquired, and what assumptions were made
in producing the plots. For me the plots raise more questions than they
answer - even when I assume that all their measurements were spot on.
Yuppers - I like O2 where I am and O3 overhead (I sunburn easily). I
confess that I have difficulty finding the /significance/ of the
absorption data as presented. My intuition tells me that the altitude
distribution of these gases is not constant, and that there may also be
geographical variances. I recall sailing in the Caribbean and noticing
that, on an otherwise clear day, each island had its own cloud; and I'm
aware that one side of a mountain range might be arid while the other
side was wet. In my experience clouds seem to range from 1,000' up to
about 50,000' - does that imply an altitude distribution for water vapor
as well? Do those same kinds of distributions manifest for the other
gases as well?
Perhaps because I lack your experience, I find myself with insufficient
information to draw any conclusions about the significance of any change
in atmospheric composition.
I provided the link, by the way, not to refute anything that you'd said
but, rather, to provide what little information I happened to have that
seemed germane. I especially appreciate the link to the ISU plots -
they've certainly provided food for thought.
Please refer to the Infrared spectrum of Carbon Dioxide
To understand the scan remember that the x axis is in wavenumbers
(2349=4.26 um) and 667.00 um.)
(See scan) While Carbon Dioxide is a strong absorber, it only absorbs in
three small sections of the Infrared band. It does not absorb in the
visible and Ultraviolet range.
The following is the same data for water vapor
There is 10 times the water vapor in the air and the bands of Carbon
Dioxide have greater absorbance, BUT water absorbs in about 70% of the
wavelengths in UV and Infrared, so because there is more total
absorbance there would be more energy absorbed.
Sort of like the amount of water getting through a couple of pin holes
in a bucket, compared to the water getting through a sieve.
ummm... do you know how much carbon dioxide we have been pumping into
the atmosphere on an annual basis? It's in the billions of tons.
Do you understand that methane is a far more serious greenhouse gas than CO2
and that cattle and other large mammals vent more methane into the
atmosphere than any other source? Are you ready to wear a fart suppressor?
OK, that was REALLY funny. You get a prize:
Tim Daneliuk email@example.com
Too Kool! The Russians!
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