RealClimate has recently added a post by Rasmus Benestad concerning the simple physics of the greenhouse effect. The post was a good read, except that its description of “simple” has been criticized throughout the comments, which has led readers to wonder exactly who the target audience was. The aim, after all, was to find an explanation for global warming that could be communicated effectively and understood without the necessity to invoke reliance on full-blown General Circulation Models. Presumably (so the comments go…) it was too technical for the general reader and too simple for those already initiated into the subject-matter, leaving a relatively small audience that can take much of substance from it. I’d like to elaborate on those criticisms below and agree and disagree with various points.
RealClimate is a high quality science website, and by now a lot of people in the scientific community are aware of its existence and it is quite common to find links to it on various academics’ homepages or university course sites. RC attracts people with all sorts of background, including
1)wingnuts who know nothing and have no desire to
2) curious students who want to learn more but don’t currently have background in atmospheric sciences or math/physics
3) curious students who know a fair amount of technical detail and still want to learn more at a somewhat high level
4) Overlapping somewhat with the last group are those commenters who know enough to answer general questions with high confidence. They are not necessarily “experts” but have been initated into the language of the field, have experience reading the primary literature or going to academic conferences, and would have the ability to speak authoritatively about certain issues to non-technical audiences. These people can stimulate very interesting discussion within the comments and clarify points of confusion that people in the previous categories have, making it much easier on the scientists such as Rasmus or Gavin from having to respond in detail to everything. “Moving forward” in understanding is probably the most difficult for this group because by this point, the resources which are easily accessible (e.g., the web) are no longer highly educational and any further detail will likely require taking several years to go to grad school or delve into upper-level textbooks.
5) Finally, there are experts who have spent decades working in the field and have learned (and work with) the very fine details of the topic in question, and can thus discuss the very nitty gritty if the comments happen to ever reach that point.
One can expand and sub-expand upon these…perhaps including children and high school age people who you want to get “listening” without overwhelming with technical details. How one falls into such broad categories of course depends on the specific topic. One can be in the last category and have expertise in ice core research yet fall in the second to last category and only have a “good enough” understanding of radiative transfer. Group 3 in particular is likely to encompass engineers, biologists, chemists, etc….people who can follow scientific arguments but don’t necessarily know a whole lot about climate change. Presumably group 2 encompasses the vast amount of readership on the climate blogosphere, and is probably a good target audience for popular discussions of the greenhouse effect. Outside of RealClimate and other sites, there is of course a much larger group in the real world: those who don’t even think about climate change. This is most people. At most you might get a few words muttered about global warming at the dinner table, maybe from watching Al Gore, but for this group it’s an issue isolated from them and not within their scope of interest. It’s not my intention in this post to describe how to get this group listening, but that’s clearly a big subject for another discussion.
I believe that it is necessary to have information available at different levels of sophistication, particularly for those people who already know the basics and want to move past simple “cartoon diagrams” of the greenhouse effect, yet at the same time have no desire to read literature at the level of Goody and Yung or go through the integrated forms of the Schwartzchild equation describing the transmission and emission of radiation through a medium.
Communicating to group 1 is not possible. It is insane to presume one can teach someone that has no intention of learning, or that you can fill their “knowledge cup” with water when it is already full of mud. It is still worthwhile to respond to their criticisms, not for group 1’s sake, but to help people in the other groups sort fact from fiction while simultaneously enhancing their own knowledge.
Concerning Rasmus’ post at RC, it is appropriate to introduce the basic concepts of radiant heat transfer (described by Planck’s law), global energy balance, the type of molecules which absorb IR, and build this up to optical-depth type of thinking. This was a good approach. It is also unclear to me who the target audience was. There was a good quote however in comment #55 by the poster “wili” who stated
It reminded me of old “Scientific American” articles from the ’70’s that I would struggle to understand as a highschooler and college student. Often I didn’t get past the first page or so, but if I really worked at it and talked about it with my nerdy, more-scientifically-literate friends, I could usually figure out most of it and felt better for the mental exercise.
Now I realize many readers may not have access to nerdy scientific friends, although RC has a comment board where it is easy to ask questions, discuss amongst groups 2/3 who can share links and ideas, and obtain answers from groups 4/5 (who also serve to to push groups 2 and 3 in the right direction should their well-intentioned curiosity start to take them to wrong answers). The argument that the post is “too technical” is not convincing, and as wili points out, work of this sort can serve as a great mental exercise for those curious about building up a more complete understanding. The post itself links to many external resources as well as other RC posts covering the same topic from different angles. This, with the help of fellow peers on the comment board, should allow most people to work through the logic of Rasmus’ post.
If the object is to use Rasmus’ approach in more accessible venues, such as general talks to college students at universities, secondary media outlets, etc then I think it is a good one although with some trial and error modifications. It is a good approach to build up a step-by-step case for the greenhouse effect and global warming where each step can be understood completely and without complicated jumps in logic. It is also reassuring to know that the argument for global warming stems from physics which has its roots in pioneering work that is over a century year old; it does not only emerge in complex computers, nor is it a “hunch” by scientists who simply seen a temperature-CO2 correlation and declared that it must be causative.
The part about feedbacks and stratospheric cooling tends to mesh discussions which are typically associated with the “amplified greenhouse effect” instead of the natural greenhouse effect itself. There is no reason they need to be exclusive, but they serve as an unnecessary point of confusion. Stratospheric cooling is sometimes helpful to point out, upon further questioning concerning the human fingerprint in global warming, but the broad picture of the greenhouse effect is not particularly sensitive to what is happening in the stratosphere. The part about negative feedbacks is unreadable to anyone who didn’t already know what feedbacks are. It is of course not possible to do justice to these details in one concise post (perhaps a multi-part series would have been better?) but if that’s the case then unnecessary complications, following the Einstein quote in the opener, are better left unmentioned.
There are different levels one can understand the greenhouse effect at. For quick and easy descriptions, such as one might communicate to a young audience or for a quick 30-second sound byte at dinner with you parents, you might leave it at “certain gases in our atmosphere absorb heat that is escaping to space making the surface warmer than it otherwise would be.” The most simple visualization is typically one which treats the atmosphere like a single slab of infrared absorbing molecules and is transparent to incoming solar radiation.
This is fine for illustrative purposes. I believe something similar to Rasmus’ post is a good next step up. I find the more sophisticated versions of the greenhouse effect tend to move the focus from a “slab” of molecules radiating energy downward to a focus on the top of the atmosphere energy balance.
Some versions, such as described in David Archer’s “Global Warming: Understanding the Forecast” and Dennis Hartmann’s “Global Physical Climatology” articulate the so-called “layer model” where you throw in a bunch of “layers” at different altitudes which radiate according to their temperature by Stefan-Boltzmann. Often they are assumed to be fully transparent in the visible and a blackbody in the IR, although this does not need to be the case, it just makes for ugly algebra (Grant Petty works through a simple example of non-unity absorptivity and emissivity in a grey atmosphere in his Radiation book). I’m not sure how helpful the “layer model” is and it usually involves a good deal of trickery to get results which make sense (e.g., “one layer still isn’t enough but adding two layers gives you the observed temperature!!”). What does this even mean with respect to the real world?
At still more complete versions, one inevitably needs to account for a convective troposphere and the spectral dependence of absorbing gases. It takes some time to build up an intuition and some higher-level reading in order to discuss the processes involved at this level, but one does not have to be in expert in group 5 to do so. Rasmus’ post serves as a useful bridge for the most simple of descriptions to the more complicated split-spectrum and lapse rate descriptions.
The aim is good communication and this requires information accessible to a broad range of audiences. The reader will have to judge for themselves whether they are equipped with the tools to handle the level of sophistication in any particular description, or how willing they are to learn, but it is very easy to find articulations of the greenhouse effect accessible to almost anyone. But I do like Rasmus’ and others suggestion that a paradigm shift should be made to articulating global warming to lay audiences through the framework of step-by-step physics.