Obviously, our discussion on math-fun last year must have generated some thinking. I was wrong about utilizing space tethered smokestacks, but Dr. Wong was right on. ----- Economist.com Global warming A stairway to heaven? May 31st 2007 | ACAPULCO
From The Economist print edition
Earth has a natural transport system standing ready to get rid of carbon dioxide. Here is how it might be turned on MOST solutions to the problem of global warming are tediously, almost oppressively, quotidian. Switch the lights off. Stop using fossil fuels to make electricity. Run an efficient car. Don't fly. A few grandiose projects have also been suggested, such as giant parasols in space or adding iron to the ocean to encourage planktonic algae to grow and soak up carbon dioxide. On the whole, though, those big ideas are either mad or could have dangerously unpredictable consequences. That does not mean that lateral thinking about the problem has no place. And the idea proposed by Alfred Wong of the University of California, Los Angeles, at last week's meeting of the American Geophysical Union, in Acapulco, is about as lateral as they come. Dr Wong reckons the problem is not so much that CO2 is being thrown away, but that it is not being thrown far enough. According to his calculations, a little helping hand would turn the Earth's magnetic field into a conveyor belt that would vent the gas into outer space, whence it would never return. The site of the conveyor Dr Wong is proposing to build is the Arctic. More specifically, he is suggesting it be over one of his workplaces, the High Power Auroral Stimulation facility near Fairbanks in Alaska that he set up 20 years ago to stimulate and study artificial auroras. The Arctic sky is special because it is one of the two places (the other being the Antarctic) where the magnetic shield of the Earth opens up to outer space. Auroras, such as the one pictured above, pleasingly testify to a stream of particles from the sun that gets through and hits the atmosphere. These particles bring with them many gigawatts of power that Dr Wong wants to harness to reduce the concentration of greenhouse gases in the atmosphere. Going up in the world His idea starts with the fact that CO2 molecules like to team up with loose electrons, to form CO2 ions. A few percent of the CO2 molecules in the air manage to find such electrons. As a result they become negatively charged. The second piece of luck is that all over the Earth there is a constant vertical electrical field. The surface and the atmosphere form a giant battery, as the lightning discharges of thunderstorms demonstrate. This field tends to make negatively charged ions, such as those of CO2, drift upward. At first this happens slowly, because collisions with other molecules keep throwing the drifting ions off course. But after a few days they arrive at an altitude, about 125km up, which is so rarefied that an ion can move freely about. This is when the last stage of their one-way trip into space begins: sailing along the magnetic field of the Earth. High in the polar regions, the lines of magnetic force point almost straight upwards. When a charged particle is in a magnetic field, it tends to travel along that field's lines of force, spiralling as it goes. In the case of a CO2 ion at an altitude of 125km, it spirals round 17 times a second. However, as it travels upwards, it experiences a weakening field. It must then make fewer turns per second, in obedience to a law of physics called the conservation of magnetic moment (this is similar to the law of conservation of angular momentum that slows a spinning ice dancer down as he spreads his arms). And because it cannot just shed its energy of movement, it is forced to travel faster and faster in the direction of the field. The eventual result is that it is ejected into space. That, at least, is the theory. And although CO2 is too rare even in today's atmosphere for the phenomenon to be detected by existing satellites, an equivalent ejection of oxygen, a far more abundant gas, can be detected from space. So it seems more than likely that Dr Wong's analysis of what is going on in nature is right. The question is, can CO2 molecules be given an artificial leg-up into space, so that they leave the atmosphere in sufficient numbers to make a difference to climate change? Dr Wong thinks they can. The leg-up he proposes comes in two stages. First, he has to ionise more CO2. There are many ways this might be done, but for a first experiment Dr Wong proposes zapping dust in the atmosphere with powerful lasers, to release electrons that can then combine with CO2. Having created the ions, he will then nudge those that have drifted upwards to the appropriate height with radio waves of exactly 17 cycles a second, which will give them a nice stock of energy at the beginning of their spiralling phase. Once they are there, Dr Wong expects the incoming stream of charged particles that cause auroras to deliver the bonus that will make the whole thing work, by dumping some of their energy into the spiralling as well. This should happen through a process called stochastic resonance: the spiralling molecules get preferential treatment, so to speak, because they stand out in what is otherwise an environment of random movements. So far, Dr Wong has only rough calculations of the energy needs of his scheme, but these suggest that his lasers and radio transmitters, even if powered by fossil-fuel generated electricity, should cause far less CO2 to be put into the atmosphere than they ship out of it. The key to this efficiency is the free energy arriving by stochastic resonance. If the particles do their bit, he thinks that a few dozen megawatts of additional electrical power is all that will be needed to make a dent in the amount of CO2. Exactly how big that dent would be, he is not yet sure. But he is pretty sure it would be big enough to help. Copyright © 2007 The Economist Newspaper and The Economist Group. All rights reserved.