Carbon Dioxide and Feedback (Guest Post)
Posted by The Diatribe Guy on April 20, 2009
The following post was submitted by Bob Heiderstadt. This is outside my area of expertise, so I make no warranties regarding all the salient points in the article. I do have a basic understanding of the dynamics of what is discussed (I have some background in Physics), and felt it to be a worthy contribution. Bob has an engineering background, and has been kind enough to correspond occasionally via e-mail with different insights or articles that he has offered for potential use on my blog. I thank Bob for his contribution. It is posted as submitted. I have only formatted it for presentation.
Carbon Dioxide and Feedback
Guest post by Bob Heiderstadt
Perhaps I’m just letting my education and training as an engineer getting in the way, but I can’t see how the Anthropogenic Global Warming (AGW) crowd can possibly prevail based on science since their main contention is that CO2 is the primary driver of climate and we are in a heap of trouble. In general, the models the AGW advocates use purport that CO2 has a positive feedback. What follows is a discussion of feedback.
In any kind of system, there can only be three kinds of net feedback possible: Positive, Negative, or None. Let’s begin with positive feedback. In a system with positive feedback, the system will be bistable, that is to say the system will peg at the extremes and stay there until the source is either removed or made more negative that the original cause. For an example of positive feedback, consider a speaker moved in front of a microphone in a concert hall. A loud squeal very quickly follows and continues until either the microphone or the speaker is moved.
If a system has no feedback, then the system is inherently unstable and unpredictable and would likely peg at either extreme. This would correspond to a switch, albeit a random one.
If a system has negative feedback, then the system is inherently stable. Nature and man-made devices are replete with negative feedback systems. Here’s a man-made example: your car – if you add fuel to the engine (assuming it is already running) more power is generated which moves the pistons faster, turning the crankshaft faster, until equilibrium is achieved. Of course, when the fuel is removed, there is less energy to push the pistons, and the engine slows. In nature, especially during the summer, mornings tend to start out clear, as the ground and air warm, clouds start to form, masking the lower atmosphere, and thereby cooling things. If there is enough water vapor in the air, and it warms up fast enough, then thunderheads form, and rain follows, cooling the ground and lower atmosphere. Clearly, even the AGW advocate has to admit that the climate has been stable in the past, since earth is neither an ice cube (sphere) or a uncontrolled hot house (Figure 1).
If CO2 is the primary driver of climate and we are headed for oblivion as the AGW advocates contend as a result of positive feedback, and since the climate has been stable in the past, then it stands to reason that the “tipping point” level of CO2 had not been reached in the past. This would mean that we would have to reach at least the previous highest level of CO2 before we have anything substantial to worry about. During the Cambrian Period (550 million years ago) the CO2 levels floated somewhere between 3000 and 8000 ppm with a probable peak around 7000 ppm; during the Early Carboniferous Period CO2 levels were around 1800 ppm. The current level of CO2 is about 400 ppm. Since the climate was stable with CO2 levels around 7000 ppm, we can safely assume that we have a long way to go to get to the “tipping point” the AGW advocates are worried about. The source of the CO2 is irrelevant, only the total CO2 is significant. If the AGW climate models are correct that we are quickly reaching the “tipping point”, then it suggests the climate is much more sensitive to CO2 levels than it was in the past. The mechanism for this increased sensitivity has yet to be explained. Oh, by the way, when the CO2 levels peaked at around 7000 ppm, the average global temperature was around 22º C (72º F). While undoubtedly not good for the existing low-lying coastal areas, the overall effect wouldn’t be disastrous for the planet.
What about negative feedback and CO2? Clearly the planet is a negative feedback system given the overall stability of the climate over the last 600 million years or so, oscillating between warm and cold periods. Were it otherwise the average global temperature would be considerably higher than it is now, possibly even approaching the temperatures on Venus. This hasn’t happened for a variety of reasons, mainly based on the physical characteristic of Earth (distance from the Sun, eccentricity of orbit, period of rotation, density of the atmosphere, and so on) differing from those of Venus. Actually, even Venus is a negative feedback system, with just a much higher stable average temperature. Does this mean that increased CO2 will have no effect? Of course not, CO2 is another input to the climate, and unless all of it is absorbed, then it will increase the density of the atmosphere slightly, trap a bit more heat, and raise the temperature of the planet by some amount. Could this be bad for Miami? Maybe, but we don’t know enough about the climate to be sure, and the computer models are still very crude in terms of predicting the future from any single input. Since there are multiple inputs, not the least is the Sun, outcomes are difficult to predict with any certainty. Progress is being made and some new interesting hypothesis have been presented, with associated predictions being tested in the only lab possible…the planet’s climate. Time and temperature will tell whose hypothesis is more correct, and whose is bunk.
In conclusion, either way it seems as though the AGW crowd is on the wrong side of the results. If they are right, the levels of CO2 need to be much higher than at present, and if they are wrong, then there will be no significant upward rise in temperature.