Its all About the Feedback

If frequent readers get any one message from this site, it should be that the theory of catastrophic global warming from CO2 is actually based on two parallel and largely unrelated theories:

  1. That CO2 acts as a greenhouse gas and can increase global temperatures as concentrations increase
  2. That the earth’s climate is dominated by strong positive feedback that multiplies the effect of #1 3,4,5 times or more.

I have always agreed with #1, and I think most folks will accept a number between 1-1.2C for a doubling of CO2 (though a few think its smaller).  #2 is where the problem with the theory is, and it is no accident that this is the area least discussed in the media.  For more, I refer you to this post and this video.  (higher resolution video here, clip #3).

In my video and past posts, I have tried to back into the feedback fraction f that models are using.  I used a fairly brute force approach and came up with numbers between 0.65 and 0.85.  It turns out I was pretty close.  Dr Richard Lindzen has this chart showing the feedback fractions f used in models, and the only surprise to me is how many use a number higher than 1 (such numbers imply runaway reactions similar to nuclear fission).


Lindzen thinks the true number is closer to -1, which is similar to the number I backed into from temperature history over the last 100 years.  This would imply that feedback actually works to reduce the net effect of greenhouse warming, from a sensitivity of 1.2 to one something like 0.6C per doubling.

13 thoughts on “Its all About the Feedback”

  1. The statement “such numbers imply runaway reactions similar to nuclear fission” is a bad analogy. Nuclear fission in a nuclear power plant is not a runaway reaction.

    Normally, it is a very controlled process defendant on specific feedbacks, such as a negative moderator temperature coefficient. As temperature goes up, negative reactivity is inserted, and power level rise is limited.

    Kind of like clouds resulting in a negative forcing, limiting global temperature rise.

    The Chernobyl design had a positive moderator temperature coefficient at low powers. As temperature went up, power went up. At higher power levels, the moderator temperature coefficient was only mildly negative, and, thus, was not able to turn the significant power rise resulting from the temperature spike at the time of incident initiation.

    Kind of like the models’ predictions of positive cloud climate formations.

  2. Mike: Nuclear fission in a power plant is a very controlled situation, unlike the natural tendency of an accumulation of a sufficient amount of the fuel. Just as the natural tendency of a deposit of coal to burn is different from its use within a coal fueled power plant. (Yes, I support nuclear power, but not the Chernobyl nor U of Chicago designs)

  3. just requested that readers submit examples of “skeptic” arguments to which they should respond. They claimed that they are growing tired of addressing the same old arguments of the skeptics. What BS.

    I suggested in comments that they address Dr. Lindzen’s powerpoint presentation and this Climate Skeptic post. I also suggested several recent blogposts from Dr. Spencer on cloud feedbacks and one by Roger Pielke regarding the heat content of the oceans. The blogposts of Spencer and Pielke referenced peer-reviewed literature to support their points. My comment was respectful and did not contain any inflamatory statements. My comment appeared for about one hour and then disappeared.

  4. If frequent readers get any one message from this site, it should be that you will never, ever grasp even the simplest concepts. Your frequent posts about feedback are all bullshit, because you haven’t been able to understand that the climate system does not respond instantly to forcings. You’re desperately intellectually ill-equipped, and sadly this is one of those cases where someone lacks the knowledge even to understand how inadequate their knowledge is.

  5. @Hunter: “If frequent readers get any one message from this site, it should be that I will never, ever grasp even the simplest concepts. My frequent posts about feedback are all bullshit, because I haven’t been able to understand that the climate system does not respond instantly to forcings. I’m desperately intellectually ill-equipped, and sadly this is one of those cases where someone lacks the knowledge even to understand how inadequate his knowledge is.”

    This is just so true.

  6. Mike,

    AnonyMoose is correct. In nuclear reactors the control rods and fission poisons (like boron in the fuel rods) absorb neutrons to prevent a runaway reaction. Without these negative feedback processes the average 2.01 neutrons produced from each fission would near instantaneously produce a mushroom cloud.

    In an environment where so many neutrons are absorbed the moderator around the fuel rods becomes important. Most pressurized water reactors (PWR, the type I worked on in the U.S. Navy) use water around the fuel rods to both and transfer heat away fro the fuel to do work and reflect neutrons back into the fuel rods. Chernobyl and U of Chicago designs used graphite as a moderator which had inherent many more risks. If a PWR loses primary coolant the reaction stops; however, the issue latent heat removal remains (as it was a TMI when the core was partially uncovered).

  7. Folks, Hunter is the one who had issues on a previous thread with the concept of feedbacks.

    Please enlighten us, O Wise Hunter, (i) how long does it take for the climate system to respond to forcings, and (ii) does this delay in response ultimately result in a higher or a lower feedback and why?

  8. In reply to Sparkey. From what I’ve read, the percentage of U235 in nuclear reactors is on the order of 3% or so. That’s enough for runaway meltdown without the control rods, but there’d be no mushroom cloud. For a nuclear explosion you need about 35 lbs of 98% pure U235.

  9. I’ve been wandering through the comments here for awhile, but never posting.
    I’m still waiting for Hunter to provide some evidence for his vitriol-lined assertions. I’ve yet to see any…

  10. One of the things that suprises me (physicist and engineer) is how many of the people in this whole AGW argument don’t seem to understand the difference between feedback and amplification. Let me explain:

    Feedback is where a change in some input parameter causes a change in an output parameter which in its turn changes the input parameter. Positive feedback will always cause some kind of runaway, and is always stopped by some non-linearity (for instance Stefan Boltzmans law decides that the earth will not melt due to runaway CO2). Negative feedback is very common, and keeps systems stable at a certain value, unless timedelays are involved in the feedback, in which case oscillations might occur. All this is described mathematically with Control Theory. The subject has been wel understood for at least a century by engineers.

    Amplification is a factor that modifies the effect of an input parameter onto the output parameter. Amplifications can have any value, positive or negative. Amplification factors can not cause runaway systems When Lindzen talks about an amplification factor of -1, he means that other mechanisms modify the original CO2 heat contribution so that the final effect on global temperature is 0.

    I once read somewhere that the climate modelers are not really aware of control theory. If they are really confusing feedback and amplification, than that’s certainly the case. That would make the outcome of their models pretty much without value.

  11. @Bart: Yeah, you can see that the earth climate oscillates if you just enlarge the time frame from years to millenia. Even then CO2 and temperature swings are lagging meaning that effects are time-delayed. But, how long is the time delay? If we look at CO2 its sometimes about several hundred years, meanning that temperature rises now would correspond to CO2 700 years ago, where man made climate was wholly through agriculture.

    However, the argument isn’t focused on this lag, because the climate scientists think that the rate of change is also important and might change the response time. I am not sure that this is correct. It depends on how big the influence is. It’s like air resistance of cars at a velocity of 15 mph against the forces necessary to accelerate the car to 30 mph. it is insignificant…

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