Now that we are deep enough into the Anthropogenic Global Warming crisis that only the whackiest of whackaloons are still denying its existence or the serious impacts it is going to have on planetary livability, a whole different type of whacky thought is filling the airwaves. These have to do with a variety of techniques to suck CO2 out of the sky and turn atmospheric carbon into something useful like carbon nanotubes or alternative fuels.
These schemes are no doubt possible. The problem is that they don’t solve the actual problem, which isn’t carbon in the air, it is about making energy by putting carbon in the air. To talk about that, we need to talk about thermodynamics.
The Laws of Thermodynamics are pretty fundamental science. They cannot, in the normal universe where we live, be violated. They were once summed up to me in this analogy which helps to keep track of them*:
1st Law: You can’t win.
2nd Law: You can’t even break even.
3rd Law: You can’t get out of the game.
The one we are most worried about here is the 2nd Law, which essentially says that any time energy changes states, there is a net increase in entropy. In other words, every time you use energy to do something, you lose a bit of energy. It is the 2nd Law that makes perpetual motion machines impossible.
Relating this to schemes to pull carbon out of the air and make it useful, it is important to realize we don’t just toss CO2 into the air for the fun of it. For the most part we do it to use the energy released when you combine carbon with oxygen, be it energy to drive our cars/planes/ships or energy to generate electricity. We do this because the act of combining carbon with oxygen releases energy in the form of heat (which is a whole different chemistry lecture we should save for Beer Friday). We can do the same thing backwards, strip the oxygen off of the carbon, but that takes energy, and (this is where the 2nd Law comes in) a little bit more energy than it produced during the original combination.
So all of those schemes you see that will turn CO2 into something useful, no matter how efficient they are, will require more energy than we gained when we created the CO2 in the first place. So it makes way more sense to simply not produce the CO2 in the first place. instead, we could use the energy we would dedicate to sucking it out of the air and making carbon nanotubes out of it back into doing whatever job we wanted to do with the energy we gained in the first place when we added the oxygen to the carbon. As a bonus, we can still make the carbon nanotubes out of any of a zillion existing carbon sources we have on the planet, be they plants, rocks, or hydrocarbons, without the need to waste a bunch of energy stripping oxygen off of the carbon. That way the carbon stays out of the atmosphere, we use less energy, and we are all better off.
The reality is that the “technological fix” of climate change is nothing shocking, cutting edge or freaky; it is in our hand right now. It is no more complicated than stopping the taking of carbon out of the ground to combine with oxygen for cheap energy when there is an abundance of alternatives available. But it starts with recognizing this “cheap” form of energy is a false economy, as is betting the future on big fans and diamonds from the sky.
*there is a 4th Law, but since it was developed later, and then determined to be more fundamental, the physics community called it the “0th Law”, just to reinforce those points. In the analogy above, it would be translated as “We are all playing the same game”