Steve Koonin had an op-ed in the Wall Street Journal a while ago called Climate science is not settled. He was also involved in initial attempts by the American Physical Society to draft a statement on climate science that Judith Curry discussed in a post a day or so ago. Judith seemed to think that his departure from the committee drafting the statement meant noone left understood things properly.
I pointed out that this seemed unlikely given how poor his article was. What I highlighted was the following.
For example, human additions to carbon dioxide in the atmosphere by the middle of the 21st century are expected to directly shift the atmosphere’s natural greenhouse effect by only 1% to 2%. Since the climate system is highly variable on its own, that smallness sets a very high bar for confidently projecting the consequences of human influences.
Interestingly, Steve Koonin has now authored a guest post on Judith’s blog, trying to explain what he meant. It all seems a little odd to me.
Typically the natural greenhouse effect is regarded as increasing effective surface temperatures by 33K, or producing a radiative forcing of 120Wm-2 (or 150Wm-2 depending on how you measure it). By the middle of the 21st century, temperatures will be expected to have risen by between 1.5oC and 2.5oC, and the net change in radiative forcings plus feedbacks will be between 6.5Wm-2 and 9.5Wm-2. So, by a standard measure the enhanced greenhouse effect will have amplified the natural greenhouse effect by between 4.5% and 7.5%, much more than the 1% to 2% claimed by Koonin.
Now, it seems that he’s decided to measure relative to a base temperature of 288K, or relative to a net downward flux at the surface of 503Wm-2. These numbers may be right, but neither would typically be regarded as a normal way to quantify the natural greenhouse effect. So, yes, relative to these numbers, it is a small change, but this isn’t the standard way to quantify the greenhouse effect and these small numbers don’t really tell you anything as to the significance of this. I did try to point this out in the comments and then made a rookie ClimateballTM mistake by trying to illustrate that even an extreme change would be regarded as small relative to these quantities. For example, a 10oC increase in surface temperature would probably make the planet uninhabitable for mammals, but would only be a 3% to 4% shift according to Koonin’s metric. Of course, I then got accussed of exaggerating etc. and everything went downhill from there.
Anyway, I’ve rambled as I normally do. What I really wanted to do was highlight an exchange, between Steve Koonin and Isaac Held, in the minutes (starting on page 433) from the Climate Change Review Workshop – held last year – of the American Physical Society (H/T Willard – I don’t know how he finds these things). It’s an interesting exchange in it’s own right, but is also relevant to this discussion (the bolds are mine).
DR. HELD: …..Some of the questions that came through in your background document I thought were a little off, if I can be frank —
DR. KOONIN: That’s fine. We are not experts.
DR. HELD: — in the sense that they don’t conform to my picture of how the climate system works. So, I have my null hypotheses. And I have been doing this for over 30 years, so I have developed a lot of hypotheses. Some of them turn out to be wrong. I don’t like this argument from complexity saying oh, it’s a chaotic system. There is all sorts — you can get a nonlinear system to do nything you want. That just doesn’t tell me anything. But whenever I look at the forced response of the climate system, it looks linear to me. And what is the best example we have of forced responses? The seasonal cycle. Seasonal cycles are remarkably linear-looking.
I grew up in Minneapolis which is why I plotted Minneapolis here. [next page] I just repeated it twice for clarity. This is just the seasonal cycle. It’s almost perfectly inside the squiggle. There is an awful lot of nonlinear fluid dynamics and cloud formation stuff going on underneath this. My analogy here is the thermodynamic limit of statistical mechanics. The smaller response, you seem to worry about the fact that the external forcing is so small, but that just makes it more likely to be linear.
DR. KOONIN: Although, in real thermodynamics, since you have a good separation of scale, there is a small parameter or a big parameter, right? The size of the atoms or the number of atoms or something?
DR. HELD: I am not saying it is as good as thermodynamics, but that’s my underlying picture. One other example of forced response that Dick referred to, we have Milankovitch. We don’t have anything really in between — I mean, we have the sunspots, but that’s hard to see, it’s so small. So, we have the seasonal cycle and Milankovitch. Those are both changes in our orbit. And that looks pretty linear, too, at least in the sense that you see the periods of the orbital changes coming out.
DR. KOONIN: If you take a given model, one of the ones in the middle of the pack, and start doing the linear study on one or several of the forces, start cranking up the solar constant or the aerosol loading or CO2, does it behave in a linear way?
DR. HELD: Yes.
DR. KOONIN: Over the range of what we are talking about?
DR. HELD: A lot of people looked at that. It’s very linear.
DR. COLLINS: Yes, it is very linear.
DR. HELD: The whole language, the whole forcing-feedback language we look at is assuming that this linear picture is useful. Otherwise, what is forcing and what is feedback? I don’t even know where to start.
DR. COLLINS: At the risk of breaking protocol, may I?
DR. KOONIN: Yes.
DR. COLLINS: You can force the model separately with different forcing agents, look at the separate response, add the response and then add the forcings and compare the total response to the total forcings. That has been done ad nauseam, not a problem.
DR. HELD: The models look pretty linear. The observed seasonal cycle, that looks linear. Even if in the Ice Age times, things look pretty linear. We don’t know that much about it. So, why should I assume that things are, gee, the anthropogenic CO2 pulse is going to interact in some exotic way with internal modes of variability? Well, it’s conceivable. But I am not convinced. I don’t think that is particularly relevant.