The Carbon Dioxide Control Knob Discussion I


Greg Tomlinson and I have been discussing in comments a blog post from last April:

Global warming XIII – The Carbon Dioxide Control Knob . I think that his comments and my replies will be informative to our readers, who aren’t likely to notice items from six months ago. Therefore, I’m going to create new blog posts each of which contains a comment and a reply with titles The Carbon Dioxide Control Knob I, II, III, and so on.

Here’s the first:

September 28, 2017 at 5:53 am Edit

You give no arguments as to what makes CO2 a primary “control knob” for the earth’s temperature, except for saying that this is what “knowledgeable people” believe. Well, the knowledgeable people I know realize this “climate change” fraud for what it is worth.

Greg Tomlinson

September 28, 2017 at 3:50 pm Edit

Mr. Tomlinson,
I’m afraid that the “knowledgeable people” you know have misinformed you.
Here’s how climate scientists and other researchers know that carbon dioxide is a key “control knob” for the Earth’s temperature. They have known this since Svante Arrhenius published research on the greenhouse effect in the 1890s.  Svante_Arrhenius and the Greenhouse effect.

The greenhouse effect is not a new phenomenon caused by human fossil fuel use. It is a natural effect, and is the reason why the Earth’s average surface temperature is about 60 F instead of 20 F, which is what it would be if there were no water vapor or carbon dioxide in the atmosphere.
The basic idea is this: The flow of energy into the Earth must balance for the temperature to be stable. The flow in comes from the Sun. The flow out comes from the Earth and appears in the far infrared. The atmosphere is transparent to most of the Sun’s radiation, which is in the visible and near infrared. But the atmosphere absorbs and re-emits substantial parts of the Earth’s upward flowing far infrared radiation. Water vapor and carbon dioxide absorb upward moving far infrared radiation and re-emit it in all directions. This reduces the amount flowing to space. Therefore, the Earth’s temperature must increase to increase the amount of upward flowing radiation leaving its surface until the flow outward equals the flow inward from the Sun. To increase its radiation, the Earth’s surface temperature must increase. That is, the globe must warm.
Natural fluctuations in the amounts of water vapor and carbon dioxide in the atmosphere produce fluctuations in the Earth’s surface temperature, as when there have been massive volcanic eruptions.
Thus actual knowledgeable people, and not your “knowledgeable people” know from fundamental principles, the 1st Law of Thermodynamics, and the detailed properties of water and carbon dioxide, that carbon dioxide is a key “control knob.”



Filed under Climate Change

6 responses to “The Carbon Dioxide Control Knob Discussion I

  1. Pingback: Global warming XIII – The Carbon Dioxide Control Knob | two heads are better

  2. How is it that CO2 is a “control knob” when H2O vapor is a much stronger greenhouse gas, both spectrally and in concentration?


  3. bleikind

    Mr. Tomlinson,
    No one says that carbon dioxide is the only control knob. It just happens to be the one that humans are rotating to the right causing the Earth’s temperature to increase.
    The greenhouse effect is a natural phenomenon that has operated throughout the Earth’s existence. Imagining the Earth’s climate as a feedback control system, we’d say that it operating for eons with on its own, gradually changing in response to natural changes, such as variations in the Earth’s orbit, solar power variations, volcanoes, plate tectonics changing ocean currents and the location of continents, and so on. Even the meteorite that wiped out the dinosaurs counts as a control knob in this sense.
    In the past 200 years, humans have increased the concentration of carbon dioxide in the atmosphere from about 280 parts per million to over 400 ppm, and we are still increasing the concentration. We have done this while all the various natural effects have continued their operation.


    • You haven’t answered my question. How is it that CO2 controls the greenhouse effect when H2O vapor is the stronger and more abundant greenhouse gas? Every time I have asked this question in the past, the answer I ultimately get involves choosing a value for temperature that supposedly includes the CO2 greenhouse effect, and then using the Clausius-Clapeyron (CC) equation to arrive at a value for H2O vapor concentration. At this point, it is argued that since the CO2 greenhouse heating affects temperature and temperature controls H2O vapor concentration, the atmospheric CO2 controls the greenhouse effect of H2O vapor as well as its own. The problem with this analysis, however, is that in applying the CC equation, we are assuming 100 percent relative humidity at all points in the atmosphere where there is CO2.

      There is also another version of this “analysis” that assumes a uniform relative humidity (not necessarily 100 percent) and then uses the CC equation to determine an H2O vapor concentration, treating the given relative humidity as the humidity at saturation. Both cases, however, involve gross misapplication of the CC equation, and therefore I do not find these arguments to be very convincing.

      So, I am interested. What’s your stand on the CO2 “control knob” theory?


      • bleikind

        There are many factors that influence the climate, and it is a metaphor to describe those factors as “control knobs.” In this metaphor, CO2 is just one of several important factors that influence the climate, the average temperature, and the weather. No one says that CO2 is the only control knob, or even that CO2 is the most important factor. CO2 happens to be that one of the available control knobs that humans have begun spinning clockwise. We, and our ruminant animals, and thawing permafrost, are also adding methane and a few other gases to the atmosphere that are important too. In the case of CO2, we’ve given that knob a 180 degree turn clockwise, so far, as the long-term natural level of CO2 was about 280 parts per million and now it is over 400 ppm. We are continuing to rotate that knob.
        These gases, including water vapor, are natural components of the atmosphere, and they fluctuate from natural causes and have always fluctuated from natural causes. As you point out, in our metaphor of the climate as a complex, nonlinear, feedback control system, some influences also influence the other factors. Thus, warming the oceans and lower atmosphere increases the water vapor content of the atmosphere. As water vapor is the most significant greenhouse gas, scientists must take this factor into account in their models. Not only does increasing the water vapor content of the atmosphere trap more long-wavelength infrared, but increasing clouds reflect more of the sun’s incoming radiation into space. Thus, whether increasing water vapor in the atmosphere increases the earth’s temperature or decreases it, is a tricky question to answer and to model.
        I haven’t made a detailed study of the various published climate models, but I doubt that your characterization of their logic is correct. Scientists know that the air is not always saturated with water vapor, and that the saturation varies in time and over the earth’s surface. In the case of water in the atmosphere, they must estimate the amount of absorption of long wave infrared going upward, and the amount of radiation reflected out to space, and the effect of water droplets evaporating and water vapor condensing on the atmosphere’s temperature. The physics of these factors is well-known.
        My stand on the “control knob” theory is that as a metaphor it is fine, and EPA Administrator Scott Pruitt, a lawyer by training, was mistaken when he told an interviewer that carbon dioxide was not a control knob. In that metaphor, the atmosphere and climate control knobs are connected among themselves not only behind the control panel but also in front of it. When a major volcanic eruption blasts aerosol into the stratosphere, turning the “high altitude aerosol” concentration control knob to the right, there is a rubber band that goes around it and the incoming solar flux control knob, with a twist in it, so the incoming flux decreases when the aerosol concentration goes up, the incoming flux knob turns to the left. When human activity puts aerosols into the atmosphere, they are turning the same control knob as the volcano, and it turns the incoming flux knob too.


  4. Pingback: Global Warming XVI: The Breadth of Evidence | two heads are better

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