Yesterday I threw up a teaser for a future post about the Super Chimney, and here it is. I can not resist the pull of this posting, it has been rattling in my head since I found the Super Chimney (via SGTU podcast #192). The site that is home to the Super Chimney is simply superchimney.org, and is run by a man named Michael Pesochinsky. I know nothing about Mr. Pesochinsky, his motives, his background, or his mental state. I can only take the site at face value, as there is no indication that it is farce, and it appears that some effort has been put into the site, excepting quite a few grammar and spelling errors.
Here is the skinny on the Super Chimney: Mr. Pesochinsky suggests that building a few (around 10) Super Chimneys of diameter 1 km and height 5 km, anthropogenic global warming will be mitigated, the world's energy problems will be solved, and carbon will be sequestered in the newly arable land that is created by rain around the chimneys. So, what is the idea, well by clicking a link to the "principle," it is quite simply explained: "Hot air rises above cold air because hot air is less dense and therefore, it is lighter than cold air." Quite right, and really the underlying principle for a surprisingly large amount of the atmospheric sciences. The Super Chimney idea simply says that you can throw up a structure with openings at the bottom and top, and hot near-surface air will rush in at the base and rise with striking speed up the chimney because the surface air is so much hotter than the air at 5 km up. Along the way, harness all the kinetic energy of the updraft by installing turbines.
The idea is simple, and at first makes sense to a lot of people, which makes it a bit dangerous. In this post, I want to address two points: (1) be skeptical of things that seem too good to be true, and (2) the Super Chimney is a ridiculous and naive idea that has no hope of working in any way.
So, the first point about being skeptical. Whenever a new idea is presented, whether a product like a "dietary supplement," a medical treatment, intelligent design, or a mitigation strategy for global warming, there are several levels of skepticism that have to be addressed. If the idea/product/etc claims to solve even one "grand challenge" problem, that is a red flag, and if the claim is that multiple important problems are solved, many, many red flags should be waving in your head. These difficult problems, the problems of all humanity, are hard to solve, and lots of people are working to solve them. Rarely does one obscure idea emerge from the din to successfully tackle an important problem. This goes back to the old saying about something being too good to be true... Also, it is good to ask whether this miraculous idea/device/medicine/etc has been vetted by the scientific community, or have the interested parties gone straight to the media or public? And consider the source itself. Is this a single person, from outside the field, or a respected professional? Does the person have any experience relevant to the topic at all, and is there any information even available about the background?
In the case of the Super Chimney, let's see if the idea really merits much consideration just based on these questions. Well, the claim is that building 10 Super Chimneys will produce arable land, sequester carbon, generate the world's energy needs, and mitigate global warming. No small feat!! So, it sounds too good to be true, and claims to solve huge problems. The source seems only to be this website, and there's no scientific publication to back up the claims. On the plus side, there are no testimonials on the site yet. Finally, Mr. Pesochinsky is not a climate scientist, and we don't really know anything about him. None of this suggests that the proposal should be considered seriously. How does it stand up to scrutiny?
To start, let's suppose that it is feasible to build towers of the size suggested (1km wide, 5km tall); there are some issues with this, but I'm totally willing to concede the engineering is possible.
Next, let's not get caught up with the end results for now, and only address the physical principle underlying the proposal.
HOT AIR RISES
Yes, hot air rises, and it is because hot air is less dense than cold air. The Super Chimney relies on hot air at the surface entering the tower and then rising because, as is stated, "As we climb up, the temperature drops 10° C (roughly 20° F) every 1000 meters." So because of this unstable situation, i.e., cold air over warm air, the warm air rises.
Hold on a second.... there's warm air at the surface -- check -- the temperature decreases with height -- check -- warm air rises -- check... BUT ALL THE AIR HIGH UP IS COLDER THAN THE AIR AT THE SURFACE!!! Everyone please don't panic, proceed to the nearest shelter, we expect the Earth's atmosphere to blow upward from the surface at supersonic speeds at any moment. Just as soon as the atmosphere realizes that the surface is warmer than the air aloft.
There is a logical fallacy going on here. The air at the surface is warmer than the air aloft, but it is not necessarily buoyant, and where it is, it does indeed rise. An important aspect of atmospheric dynamics exactly involves instability and convection, with the take-home message that convection acts to eliminate instability. This really means that the atmosphere will convect, i.e., air will rise, as long as it can and then it will stop.
Imagine you take a blob of warm air from the surface up to some height, and you do it such that all the energy in the blob is retained. Physically, this transformation has to change the temperature of the air in the blob. When you are done moving the blob and you measure the temperature inside the blob and outside the blob (at the same height), if the temperature of the blob is greater than the environment, it is buoyant and could continue to rise, but if it has cooled to a temperature less than the environment it would sink. We'd say that in the former case the blob is unstable to this "adiabatic" transformation while the latter situation is stable. The way that meteorologists make this kind of problem simple is by defining alternative temperatures; in this case the quantity that would be of particular value would be the potential temperature, which is simply the temperature air would have if it were brought to a reference height in this kind of transformation. It turns out to be very easy to derive an equation that says that the temperature decreases by 10 degrees C per about 1000 m of height with no vertical motion. That explains why the air above the surface is colder than the air at the surface without being unstable; in a dry atmosphere this would be the situation everywhere, but it turns out that the condensation of water changes this temperature change, and for the tropics and sub-tropics the change is more like 6.5 degrees of cooling for every 1000m of height.
The fact that the surface air is NOT unstable to vertical displacements makes the Super Chimney idea fall flat. Of course, if you warm the air at the surface enough, it will become unstable and rise, but doing so requires pumping energy into the air, and removes any benefits that could be achieved by the chimney. It simply can not work.
There are a host of other potential problems with the physics of the Super Chimney idea. In fact, every claim that is made on that site is suspect, and most of them are demonstrably wrong.
Unfortunately, given the fundamental flaw in the premise of the Super Chimney, it is impossible to address many of the outrageous claims made. For instance, take the idea that the venting air at the top of the chimney would cool down, condense water vapor, and rain in the vicinity of the tower. My first thought is that, no, this won't happen, you will really get the cloud forming inside the tower, and rising up out of it. However, that requires the air within the tower to have a reasonable temperature profile, which immediately invalidates the crazy claims of a constant updraft of more than 100 m/s. If you did have an updraft in the tower, though, the cloud base would form about where liquid water can exist, which in most environments would be around 1-2km above the surface. The result would be, among other things, a downpour within the tower itself which would cool the lower part of the tower as liquid water fell into the warm air and evaporated, and this would stabilize the column by cooling the low levels. You could actually then imagine outflow from the the base of the tower! (And, by similar reasoning to the original Super Chimney idea, maybe you could then pump cold air down to the surface and solve global warming via refrigeration!)
Another ludicrous claim is that just 10 of these towers would dramatically alter the Earth's climate. Just from a scaling perspective, this can be dismissed. A single tropical thunderstorm is an updraft that reaches from near the surface up to 15km or so, and is several km in diameter. There are thousands of such storms at any given time across the tropics. Yes the energy contained within them is enormous, but the idea that just putting 10 small, but intense storms in fixed locations and expecting them to completely change the temperature structure of the atmosphere is beyond the pale.
In retrospect, I probably should have ignored this topic, as the more I look at that site and think about it, the more and more crazy it is. The whole thing is based on completely misunderstanding the basic physics of the atmosphere, and that is even before we start considering the implications for global warming or energy production. The lesson to be learned is that if an idea doesn't pass snuff on the basic skeptical questions, it probably isn't worth digging into it in any depth, at risk of your own mental well-being. However, just as a reminder that craziness can have consequences, I suggest checking out the website WhatsTheHarm.net.