UCAR CO2 Diagrams

Related to the UCAR Very, Very Simple Climate Model is their Carbon Dioxide 400 ppm Atmospheric Concentration Diagrams. This is accessed via a link from the related activity page - click the Background & Extensions tab and scroll to the bottom of the page. The page starts off pretty good, and truly attempts to explain (demonstrate) how much CO2 is in the atmosphere.

But, in my opinion, it stops too soon - there are a couple of images missing.

Before continuing with this page, I strongly suggest studying the UCAR page and see what you think. Then continue here to see what I think the issues are.

The basic model | Lets show some water vapor - 1st try Use 89.7% of width CO2 bar 4 pixels wide Comments | Venus | Feedbacks | Comments

The basic model

They are using a 600 by 400 rectangle to represent the atmosphere and indicating the amount of CO2 by changing the color of a few pixels, As far as it goes - their math is correct.

They then display this in two different ways.

  1. Individual pixels are displayed at random - however, the 2 colors are too similar, more contrast would help
  2. All the pixels are shown in a 12 by 8 rectangle
Then they discuss the other gasses in the atmosphere - eventually displaying them as colored rectangles (repeated below).

Earth's atmospheric compsition

In this image, 28ppm is equivalent to 6.7 pixels. My only complaint up to this point is that they didn't separate out methane - the other "Anthropogenic Global Warming" boogieman. According to Google, it is currently 0.00017% (1.7 ppm) which would be displayed as 0.4 pixels.

Lets show some water vapor

In climate science, the question is not The better question is The UCAR page tries to explain how much CO2 is in the atmosphere - and I think they do a pretty good job. However, Yes, water vapor is mentioned in the text, but leaving it out of the final image is what, in my opinion, makes their presentation one-sided propaganda.

So, it is easy to criticize others, but what would make this better?

1st try

One possibility would be to draw water vapor across 60% of the image at the correct height and then show CO2 at the same height - for a fair comparison.

So, using the same 600 by 400 rectangle to represent the atmosphere,

Earth's atmospheric compsition - with water vapor at 60%

Use 89.7% of width

Why 60%? - Its just a swag. The atmosphere is not 100% IR opaque due to water vapor and clouds, and clouds cover about 50% of the surface. So I picked a number - other numbers might be better. To get a better comparison, the actual absorption values might be used.

According to the energy balance diagram by Kiehl and Trenberth (1997 - via IPCC AR4), of the estimated 390 W/m^2 emitted from the surface, 350 W/m^2 are absorbed by the atmosphere - 89.7% is absorbed.

(Kevin E. Trenberth (USA) and Philip D. Jones (UK) were the lead authors for "Climate Change 2007: Working Group I: The Physical Science Basis")

Earth's atmospheric compsition - with water vapor plus CO2 as 90% of width

In this case, the width of the bars approximates the amount of IR energy absorbed by each constituent. (See the spectra overlap discussion below.) The blue gaps indicate the amount of energy escaping directly to space - about 10% of the total emitted by the Earth.

CO2 bar 4 pixels wide

Another way to display this would be to make the CO2 bar 4 pixels wide (to represent 400ppm) and then compute how wide a water bar of the same height would be.

Earth's atmospheric compsition - with water vapor as 4 pixels

I like this image since it makes it easy to visualize that each additional 100ppm of CO2 increases the width of its bar by only one pixel.


All 3 of these images (models) tend to get the idea across - water vapor is, by far, the most important greenhouse gas (IR active gas). Something you might want to hide if the intent is propaganda - not science.

In all 3, water vapor is set to 2% of the atmosphere. Their page states that water vapor normally varies from 1% to 4%, and, with the images above, the reader can mentally cut the displayed value in half, or double it, as appropriate.

In my opinion, these images clearly show that adding more CO2 to the atmosphere is totally insignificant, mainly because the natural variation in water vapor is so much larger than the amount of CO2 added by humans.

On the other hand, in the stratosphere, water vapor is typically below 5ppm and CO2 (at 400ppm) is the major IR active gas. At that altitude, changes in CO2 are very significant. But that isn't the "Anthropogenic Global Warming" argument.

The UCAR page doesn't mention the fact that the relative amount of water vapor decreases with altitude. In fact, the 1% to 4% values are only for the lower troposphere - the part from the surface to around one kilometer above it. Above that, the amount (the mixing ratio) decreases significantly.

Near the surface, the water vapor and CO2 spectra overlap. As a result, it would be more accurate to represent about half of the CO2 absorption (bar width) as being absorbed by water vapor. Since the amount of overlap is a complex function of temperature, pressure, and mixing ratio, above some point, those two spectra no longer overlap. I have that programmed into my models, but it is too complex to show in these images.

Since the majority of the rest of the atmosphere is IR transparent, with respect to "global warming", it is irrelevant (except for the 0.4 pixel for methane - CH4). (Nitrogen, oxygen, argon, neon, helium, krypton, and hydrogen don't absorb or emit IR energy at the frequencies emitted by the Earth's surface.)

Note that adding water vapor to the images should reduce the amounts of oxygen, argon, and carbon dioxide displayed. However, since the amount of water vapor varies significantly with altitude, and because this is for instructive purposes only, I have not made those adjustments.


It was once frequently stated that And true - Venus does have a lot of CO2 in its atmosphere - but How much?

For a column of air between the surface and space, the temperature and pressure vary with height. To simplify the analysis and to make comparisons easier, it is convenient to determine how long a horizontal tube at a single temperature and pressure would need to be to hold the same amount of air that actually exists in vertical column. I have selected STP (standard temperature and pressure) as Earth sea level and 15°C. (There are actually many definitions of STP.) Based on these calculations, at STP, a horizontal tube about 5.3 miles long will hold the same amount of air as the entire amount of air above that point, assuming the same cross sectional area. (Of course, the temperature will cause the length to vary a lot.) For a column of atmosphere on Venus, if placed in a similar hypothetical tube on Earth, also at sea level and 15°C, the tube would be about 324 mile long. Since the Venusian atmosphere is about 96.5% CO2, just the CO2 part of that column would be about 312 miles long. Taking a ratio indicates that the amount of CO2 on Venus is about 58.9 times the entire atmosphere on Earth.

Using the diagrams above, and assuming that the CO2 bar for Venus has a width of 600 pixels (the width used for the total Earth atmosphere), the height of just the CO2 would be 400 * 58.9 = 23,560 pixels. Assuming that 400 pixels (the height of the images above) is about 3.6 inches (will most likely be different on your display),

Thus, to display the amount of CO2 on Venus using the same model UCAR used to show the amount of CO2 on Earth would require a computer monitor over 17 feet tall.

To be clear, Venus has a lot of CO2.

In my opinion, this simple example explains why we seldom hear that "we will be just like Venus" anymore - with the notable exception of Stephen Hawking.

Hopefully, this page explains at least a part of why I don't agree.


The UCAR page is fairly straight forward and does not discuss feedbacks. However, once water vapor is added to the images, it is easier to visualize the suggested water vapor feedback, and perhaps easier to explain why their analysis must be wrong.

It is frequently argued by those that believe in Anthropogenic Global Warming caused by increased CO2 that

This is known as "positive feedback". If that were true - if it really happened that way - this planet would have burned up long ago.

Since we are here, that is not how the system works. Stable systems, like the ones that support life, exhibit a strong "negative feedback" where any change in a forcing causes something that tries to reduce the forcing. If we assume that the sun affects the temperature

Simply evaporating water requires a lot of energy. As more water evaporates, that energy can not be used to increase the temperature - an obvious negative feedback.

In the images above, water vapor is shown as about 2% of the atmosphere. In reality, it varies locally from about 1% to 4%, with the higher amounts being in the hottest locations - a very strong correlation. However, it should be obvious from the image where water vapor is about 90% of the image width that doubling the amount of water vapor in the atmosphere will not cause 180% of the available energy to be absorbed. Instead, the increase is only about 9%. But, because the water vapor and CO2 spectra overlap, the total increase is actually only about 7% since the water vapor is now absorbing radiation previously absorbed by CO2. (The 9% and 7% values are from a program I wrote. There are a lot of assumptions in those calculations that are beyond the scope of this article - some of which I know are bad. However, I don't expect the relative values to be significantly different from those.)

So what actually happens is that there may be a small increase in the energy stored in the lower atmosphere, but, due to convection and clouds, there is a very significant increase in the heat released to space from the tops of those clouds. These Atmospheric Heat Pipes produce a very strong negative feedback. (Hint - deserts are hot because there is no water to evaporate.)


So - Is the UCAR page propaganda or not?

One of the common skeptic arguments is that water vapor has a much larger effect on the climate than CO2. To bury a comment about water vapor in the text, but to then leave it out of the images ... Well, that is why I consider their page to be propaganda. Nothing in it is actually wrong (or un-scientific), but it intentionally creates a misleading impression of the importance of CO2.

At any rate, to me, that omission IS un-scientific propaganda.

The same goes for Venus - if you are explaining how much CO2 is in the atmosphere, then how about putting it in context with the once common claim that "we are going to be just like Venus"?

And they call me unscientific and despicable.

Perhaps this should be filed under - Lying with the Truth!

Author: Robert Clemenzi
URL: http:// questionable-science.com / Global_Warming / UCAR_CO2_Diagrams.html