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.
Source: http://www.economist.com/science/displaystory.cfm?story_id=9253976