Does CO2 really drive global warming?

May 2001 Chemical Innovation, May 2001, Vol. 31, No. 5, pp 44—46 ^ | May 2001 | Robert H. Essenhigh, E. G. Bailey Professor of Energy Conversion, Ohio State University

[E. Pluribus Unum]

Does CO₂ really drive global warming?

I don’t believe that it does.

To the contrary, if you apply the IFF test—if-and-only-if or necessary-and-sufficient—the outcome would appear to be exactly the reverse. Rather than the rising levels of carbon dioxide driving up the temperature, the logical conclusion is that it is the rising temperature that is driving up the CO₂ level. Of course, this raises a raft of questions, but they are all answerable. What is particularly critical is distinguishing between the observed phenomenon, or the “what”, from the governing mechanism, or the “why”. Confusion between these two would appear to be the source of much of the noise in the global warming debate.

In applying the IFF test, we can start with the clear correlation between the global CO₂ profile and the corresponding temperature signature. There is now in the literature the report of a 400,000-year sequence clearly showing, as a phenomenon, that they go up—and down—together (1). The correlation is clear and accepted. But the causation, the mechanism, is something else: Which is driving which?

Logically, there are four possible explanations, but only two need serious consideration, unless they both fail.

• Case 1: CO₂ drives the temperature, as is currently most frequently asserted; and

• Case 2: Temperature drives the level of CO₂.

Both appear at first to be possible, but both then generate crucial origin and supplementary questions. For Case 1, the origin question is: What is the independent source of CO₂ that drives the CO₂ level both up and down, and which in turn, somehow, is presumed to drive the temperature up and down? For Case 2, it is: What drives the temperature, and if this then drives the CO₂, where does the CO₂ come from? For Case 2, the questions are answerable; but for Case 1, they are not.

Consider Case 2. This directly introduces global warming behavior. Is global warming, as a separate and independent phenomenon, in progress? The answer, as I heard it in geology class 50 years ago, was “yes”, and I have seen nothing since then to contradict that position. To the contrary, as further support, there is now documentation (that was only fragmentary 50 years ago) of an 850,000-year global-temperature sequence, showing that the temperature is oscillating with a period of 100,000 years, and with an amplitude that has risen, in that time, from about 5 °F at the start to about 10 °F “today” (meaning the latest 100,000-year period) (2). We are currently in a rise that started 25,000 years ago and, reasonably, can be expected to peak “very shortly”.

On the shorter timescales of 1000 years and 100 years, further temperature oscillations can be seen, but of much smaller amplitude, down to 1 and 0.5 °F in those two cases. Nevertheless, the overall trend is clearly up, even through the Little Ice Age (~1350–1900) following the Medieval Warm Period. So the global warming phenomenon is here, with a very long history, and we are in it. But what is the driver?

Arctic Ocean model
The postulated driver, or mechanism, developed some 30 years ago to account for the “million-year” temperature oscillations, is best known as the “Arctic Ocean” model (2). According to this model, the temperature variations are driven by an oscillating ice cap in the northern polar regions. The crucial element in the conceptual formulation of this mechanism was the realization that such a massive ice cap could not have developed, and then continued to expand through that development, unless there was a major source of moisture close by to supply, maintain, and extend the cap. The only possible moisture source was then identified as the Arctic Ocean, which, therefore, had to be open—not frozen over—during the development of the ice ages. It then closed again, interrupting the moisture supply by freezing over.

So the model we now have is that if the Arctic Ocean is frozen over, as is the case today, the existing ice cap is not being replenished and must shrink, as it is doing today. As it does so, the Earth can absorb more of the Sun’s radiation and therefore will heat up—global warming—as it is doing today, so long as the Arctic Ocean is closed. When it is warm enough for the ocean to open, which oceanographic (and media) reports say is evidently happening right now, then the ice cap can begin to re-form.

As it expands, the ice increasingly reflects the incoming (shorter-wave) radiation from the sun, so that the atmosphere cools at first. But then, the expanding ice cap reduces the radiative (longer-wave) loss from the Earth, acting as an insulator, so that the Earth below cools more slowly and can keep the ocean open as the ice cap expands. This generates “out-of-sync” oscillations between atmosphere and Earth. The Arctic Ocean “trip” behavior at the temperature extremes, allowing essentially discontinuous change in direction of the temperature, is identified as a bifurcation system with potential for analysis as such. The suggested trip times for the change are interesting: They were originally estimated at about 500 years, then reduced to 50 years and, most recently, down to 5 years (2). So, if the ocean is opening right now, we could possibly start to see the temperature reversal under way in about 10 years.

What we have here is a sufficient mechanistic explanation for the dominant temperature fluctuations and, particularly, for the current global warming rise—without the need for CO₂ as a driver. Given that pattern, the observed CO₂ variations then follow, as a driven outcome, mainly as the result of change in the dynamic equilibrium between the CO₂ concentration in the atmosphere and its solution in the sea. The numbers are instructive. In 1995, the Intergovernmental Panel on Climate Change (IPCC) data on the carbon balance showed ~90 gigatons (Gt) of carbon in annual quasi-equilibrium exchange between sea and atmosphere, and an additional 60-Gt exchange between vegetation and atmosphere, giving a total of ~150 Gt (3). This interpretation of the sea as the major source is also in line with the famous Mauna Loa CO₂ profile for the past 40 years, which shows the consistent season-dependent variation of 5–6 ppm, up and down, throughout the year—when the average global rise is only 1 ppm/year.

In the literature, this oscillation is attributed to seasonal growing behavior on the “mainland” (4), which is mostly China, >2000 mi away, but no such profile with that amplitude is known to have been reported at any mainland location. Also, the amplitude would have to fall because of turbulent diffusive exchange during transport over the 2000 mi from the mainland to Hawaii, but again there is lack of evidence for such behavior. The fluctuation can, however, be explained simply from study of solution equilibria of CO₂ in water as due to emission of CO₂ from and return to the sea around Hawaii governed by a ±10 °F seasonal variation in the sea temperature.

Impact of industrialization
The next matter is the impact of fossil fuel combustion. Returning to the IPCC data and putting a rational variation as noise of ~5 Gt on those numbers, this float is on the order of the additional—almost trivial (<5%)—annual contribution of 5–6 Gt from combustion of fossil fuels. This means that fossil fuel combustion cannot be expected to have any significant influence on the system unless, to introduce the next point of focus, the radiative balance is at some extreme or bifurcation point that can be tripped by “small” concentration changes in the radiation-absorbing–emitting gases in the atmosphere. Can that include CO₂?

This now starts to address the necessity or “only-if” elements of the problem. The question focuses on whether CO₂ in the atmosphere can be a dominant, or “only-if” radiative-balance gas, and the answer to that is rather clearly “no”. The detailed support for that statement takes the argument into some largely esoteric areas of radiative behavior, including the analytical solution of the Schuster–Schwarzschild Integral Equation of Transfer that governs radiative exchange (5–7), but the outcome is clear.

The central point is that the major absorbing gas in the atmosphere is water, not CO₂, and although CO₂ is the only other significant atmospheric absorbing gas, it is still only a minor contributor because of its relatively low concentration. The radiative absorption “cross sections” for water and CO₂ are so similar that their relative influence depends primarily on their relative concentrations. Indeed, although water actually absorbs more strongly, for many engineering calculations the concentrations of the two gases are added, and the mixture is treated as a single gas.

In the atmosphere, the molar concentration of CO₂ is in the range of 350–400 ppm. Water, on the other hand, has a very large variation but, using the “60/60” (60% relative humidity [RH] at 60 °F) value as an average, then from the American Society of Heating, Refrigerating and Air-Conditioning Engineers standard psychrometric chart, the weight ratio of water to (dry) air is ~0.0065, or roughly 10,500 ppm. Compared with CO₂, this puts water, on average, at 25–30 times the (molar) concentration of the CO_2, but it can range from a 1:1 ratio to >100:1.

Even closer focus on water is given by solution of the Schuster–Schwarzschild equation applied to the U.S. Standard Atmosphere profiles for the variation of temperature, pressure, and air density with elevation (8). The results show that the average absorption coefficient obtained for the atmosphere closely corresponds to that for the 5.6–7.6-µm water radiation band, when water is in the concentration range 60–80% RH—on target for atmospheric conditions. The absorption coefficient is 1–2 orders of magnitude higher than the coefficient values for the CO₂ bands at a concentration of 400 ppm. This would seem to eliminate CO₂ and thus provide closure to that argument.

This overall position can be summarized by saying that water accounts, on average, for >95% of the radiative absorption. And, because of the variation in the absorption due to water variation, anything future increases in CO₂ might do, water will already have done. The common objection to this argument is that the wide fluctuations in water concentration make an averaging (for some reason) impermissible. Yet such averaging is applied without objection to global temperatures, when the actual temperature variation across the Earth from poles to equator is roughly –100 to +100 °F, and a change on the average of ±1 °F is considered major and significant. If this averaging procedure can be applied to the atmospheric temperature, it can be applied to the atmospheric water content; and if it is denied for water, it must, likewise, be denied for temperature—in that case we don’t have an identified problem!

What the evidence shows
So what we have on the best current evidence is that

• global temperatures are currently rising;

• the rise is part of a nearly million-year oscillation with the current rise beginning some 25,000 years ago;
• the “trip” or bifurcation behavior at the temperature extremes is attributable to the “opening” and “closing” of the Arctic Ocean;
• there is no need to invoke CO₂ as the source of the current temperature rise;
• the dominant source and sink for CO₂ are the oceans, accounting for about two-thirds of the exchange, with vegetation as the major secondary source and sink;

• if CO₂ were the temperature–oscillation source, no mechanism—other than the separately driven temperature (which would then be a circular argument)—has been proposed to account independently for the CO₂ rise and fall over a 400,000-year period;
• the CO₂ contribution to the atmosphere from combustion is within the statistical noise of the major sea and vegetation exchanges, so a priori, it cannot be expected to be statistically significant;
• water—as a gas, not a condensate or cloud—is the major radiative absorbing–emitting gas (averaging 95%) in the atmosphere, and not CO₂;

• determination of the radiation absorption coefficients identifies water as the primary absorber in the 5.6–7.6-µm water band in the 60–80% RH range; and
• the absorption coefficients for the CO₂ bands at a concentration of 400 ppm are 1 to 2 orders of magnitude too small to be significant even if the CO₂ concentrations were doubled.

The outcome is that the conclusions of advocates of the CO₂-driver theory are evidently back to front: It’s the temperature that is driving the CO₂. If there are flaws in these propositions, I’m listening; but if there are objections, let’s have them with the numbers.

References

1. Sigman, M.; Boyle, E. A. Nature 2000, 407, 859–869.
2. Calder, N. The Weather Machine; Viking Press: New York, 1974.

3. Intergovernmental Panel on Climate Change. Climate Change 1995: The Science of Climate Change; Houghton, J. T., Meira Filho, L. G., Callender, B. A., Harris, N., Kattenberg, A., Maskell, K., Eds.; Cam bridge University Press: Cambridge, U.K., 1996.
4. Hileman, B. Chem. Eng. News 1992, 70 (17), 7–19.
5. Schuster, A. Astrophysics J. 1905, 21, 1–22.

6. Schwarzschild, K. Gesell. Wiss. Gottingen; Nachr. Math.–Phys. Klasse 1906, 41.
7. Schwarzschild, K. Berliner Ber. Math. Phys. Klasse 1914, 1183.
8. Essenhigh, R. H. On Radiative Transfer in Solids. American Institute of Aeronautics and Astronautics Thermophysics Specialist Conference, New Orleans, April 17–20, 1967; Paper 67-287; American Institute of Aeronautics and Astronautics: Reston, VA, 1967.

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Robert H. Essenhigh is the E. G. Bailey Professor of Energy Conversion in the Department of Mechanical Engineering, Ohio State University, 206 W. 18th Ave., Columbus, OH 43210; 614-292-0403; essenhigh.1@osu.edu.

[M. Dodge Thomas]

"As a matter of fact, there is every reason to believe we are on the cusp of the next Ice Age, which may well have been delayed by any anthropogenic global warming there might be."

Could be.

"Exactly what global temperature (a fraudulent measurement to begin with) are we supposed to hold the earth at?"

Excellent question.

"Will it be the job of geniuses like you to regulate the production of greenhouse gases to make sure the earth is not to hot and not too cold but just right?

It's clearly going to be someone's decision - in fact, such decisions are already being taken.

What's your proposal about how they should be made?

[E. Pluribus Unum]

What's your proposal about how they should be made?

Anybody who purports to be so omniscient that they know how to control the global climate is a charlatan and needs to be exposed as such.

Or burned at the stake as a witch.

[M. Dodge Thomas]

"Anybody who purports to be so omniscient that they know how to control the global climate is a charlatan and needs to be exposed as such."

IMO that would be more persuasive as:

"Anybody who purports to be so omniscient that they know how to intelligently control the global climate is a charlatan and needs to be exposed as such.

About that, you might be right. OTOH, as it appears likely to me that we not only can but are affecting global climate, the relevant questions is:

"What is the most intelligent way to affect it?".

To which "We don't yet know enough to make an intelligent decision, and then therefore we should currently do nothing." seems to me a defensible answer.

But that's not that same as saying "There is absolutely no evidence that we might be able to do it.", IMO a position which pretty much deals you out of the rest of the game, and thus a risky one to take given that the weight of scientific opinion is almost entirely on the other side.

"Or burned at the stake as a witch."

As someone concerned about AGW, I of course can't approve of acts which add to the global carbon load.

[E. Pluribus Unum]

To which "We don't yet know enough to make an intelligent decision, and then therefore we should currently do nothing." seems to me a defensible answer.

Which side are you on? :^)

[M. Dodge Thomas]

"Which side are you on? :^)"

I believe I'm on the side of caution. We have only one terrestrial atmosphere on which to conduct our experiment and only get to try the experiment once, so IMO it’s wise of attempt to model out results in advance and not attempt experiments which our models suggests have a high probability of undesirable or unpredictable results.

To me, the current evidence strongly suggests that absent other factors given human inputs into the atmosphere within a the likely range, we are looking at high (90 %+) probability of a .5-1.5 C rise over the next hundred years.

So IMO at this point the useful discussion is about things like: is warming perhaps desirable (or, is AGW possibly preventing undesirable cooling? Or, assuming not, do we have the wisdom/means to act intelligently on the knowledge or should we wait a few years?

[E. Pluribus Unum]

I believe I'm on the side of caution.... To me, the current evidence strongly suggests that absent other factors given human inputs into the atmosphere within a the likely range, we are looking at high (90 %+) probability of a .5-1.5 C rise over the next hundred years.

According to Richard Lindzen, Alfred P. Sloan Professor of Meteorology at the Massachusetts Institute of Technology:

Indeed, one overlooked mystery is why temperatures are not already higher. Various models predict that a doubling of CO2 in the atmosphere will raise the world's average temperature by as little as 1.5 degrees Celsius or as much as 4.5 degrees. The important thing about doubled CO2 (or any other greenhouse gas) is its "forcing"—its contribution to warming. At present, the greenhouse forcing is already about three-quarters of what one would get from a doubling of CO2. But average temperatures rose only about 0.6 degrees since the beginning of the industrial era, and the change hasn't been uniform—warming has largely occurred during the periods from 1919 to 1940 and from 1976 to 1998, with cooling in between. Researchers have been unable to explain this discrepancy.

Modelers claim to have simulated the warming and cooling that occurred before 1976 by choosing among various guesses as to what effect poorly observed volcanoes and unmeasured output from the sun have had. These factors, they claim, don't explain the warming of about 0.4 degrees C between 1976 and 1998. Climate modelers assume the cause must be greenhouse-gas emissions because they have no other explanation. This is a poor substitute for evidence, and simulation hardly constitutes explanation. Ten years ago climate modelers also couldn't account for the warming that occurred from about 1050 to 1300. They tried to expunge the medieval warm period from the observational record—an effort that is now generally discredited. The models have also severely underestimated short-term variability El Niño and the Intraseasonal Oscillation. Such phenomena illustrate the ability of the complex and turbulent climate system to vary significantly with no external cause whatever, and to do so over many years, even centuries.

The models don't seem to work very well, yet, according to you, we are to believe and act upon them because it would be too dangerous to do otherwise.

A new Ice Age would be an equal catastrophe, arguably worse than global warming, with wholesale starvation throughout the world. Isn't it dangerous to not be simultaneously pursuing ways to warm the earth when this interglacial comes to an end?

We have the most reliable model of all upon which to base the inevitability of the next Ice Age: historical record.

Shouldn't we err on the side of caution when it comes to global cooling as well?

[CPT Clay]

could you add me to your ping list?

[E. Pluribus Unum]

Look at this one.

You can clearly see that CO₂ levels lag behind temperature levels, meaning that atmospheric CO₂ is a RESULT of global temperatures, not a cause.

[bethtopaz]

And refuse to worry about the real threat - Islamofacism!

[Tolerance Sucks Rocks]

could you add me to your ping list?

Ask DaveLoneRanger; he actually keeps the list.

[Excellence]

The colors are logical, too. CO2 is blue, temperature red. Thank you.

[E. Pluribus Unum]

If atmospheric CO₂ drives global temperatures, why does the Vostok ice core data show changes in atmospheric CO₂ levels lagging behind temperatures?

[E. Pluribus Unum]

The Mauna Loa CO₂/temperature data clearly shows that CO₂ levels are affected by perfectly normal seasonal temperature changes. What is missing from the data is the temperature of the ocean. A gradual increase in the ocean's temperature would completely explain the observed increase in atmospheric CO₂. WHY IS THE OCEAN TEMPERATURE NOT INCLUDED IN THIS DATA? IT IS INVALID WITHOUT THIS INFORMATION!

[M. Dodge Thomas]

"The Mauna Loa CO2/temperature data clearly shows that CO2 levels are affected by perfectly normal seasonal temperature changes"

The annual CO2 cycle at Mauna Loa is tracking yearly temperature changes indirectly as a secondary effect (plant growth and decay), not the capture/retention of CO2 in the ocean or another direct "geophysical" event.

[I got the rope]

You also have to remember that these proxy studies have not been updated.

The updated proxy data shows no excessive warming.

[I got the rope]

No...but it does talk about forcing. In one paper he points to CO2 as being a driver...in the latest he points to the sun.

[M. Dodge Thomas]

A common mistake made by AGW skeptics is the assumption that only one thing can be happening at once (“There has been repeated warming in the past, therefore increased atmospheric CO2 cannot be the cause of warming observed in the present”) or that a given factor acts in the same manner under all actual conditions (“Atmospheric CO2 is supposed to cause warming, but atmospheric CO2 trailed previous interglacial warming periods, therefore CO2 could not have been their cause, but is rather an effect”), or both.

For example in the case of inter-glacial warming, what appears to have occurred is that some factor(s) other than increased CO2 (there are several candidates) caused the start of a warming period.

After an 800 year lag, CO2 concentration started to climb (one possible cause of the lag is that this is approximately the time required to achieve close to a 100% “flush” of the oceans, a result of deep ocean circulation rates).

Once the CO2 levels did start to rise, “conventional” modeling suggests that greenhouse effects (primarily caused by increased CO2, CH4 and N2O) acted as “amplifiers”, producing about 50% of the total warming during the remaining 4000 years of interglacial transition – a
contribution BTW, not much dissimilar to the estimated contribution of increased “greenhouse gasses” to warming over the next century, a situation I which we are superimposing AGW on top of whatever else is “naturally” occurring.

[I got the rope]

To me, the current evidence strongly suggests that absent other factors given human inputs into the atmosphere within a the likely range, we are looking at high (90 %+) probability of a .5-1.5 C rise over the next hundred years.

LOL. Current evidence based on empirical evidence or based on expert judgement?

You've been reading the fourth assessment report haven't you?

[M. Dodge Thomas]

"No...but it does talk about forcing..."

Sorry, I've sorta' lost track over the last week, what is "it".

[I got the rope]

Once the CO2 levels did start to rise, “conventional” modeling suggests that greenhouse effects (primarily caused by increased CO2, CH4 and N2O) acted as “amplifiers”, producing about 50% of the total warming during the remaining 4000 years of interglacial transition – a contribution BTW, not much dissimilar to the estimated contribution of increased “greenhouse gasses” to warming over the next century, a situation I which we are superimposing AGW on top of whatever else is “naturally” occurring.

I could make a model show anything. How do we verify these conventional models? I know how and I believe I mentioned it.

You should really write an expert. He really is a nice guy. It may take him a few weeks to get back to you, but I'm sure he won't mind helping you understand that this is all madness.

He's name is Dr. Ian Clark.