| > scrub atmospheric carbon I've seen this phrasing frequently in regards to carbon sequestration and it always seems to wildly understate the real problem with removing CO2 from the atmosphere. CO2 isn't some unnecessary byproduct of creating energy, compared to say soot in wood burning. The CO2 created is an essential part of the carbon cycle by which all living things store and release solar energy. CO2 + H2O + (Solar) Energy => Hydrocarbons + O2. This is how energy is stored on our planet from the energy in a high calorie soda to petroleum (okay technically sugar is not a hydrocarbon, but the idea still holds). When we extract energy from foods, burning organic material, or fossil fuels we do so by reversing that equation: Hydrocarbons + 02 => CO2 + H2O + Energy To "scrub" carbon necessarily requires more energy than we got out of the process in the first place. Photosynthesis, for example, is only 4% efficient. Which means it takes about 25x as much solar energy to build the log you burn then the heat and light you experience burning the log. "Scrubbing" CO2 fundamentally requires tremendous amounts of energy, and more than we got from the energy source in the first place. There are natural processes, like rock weathering, than can do this without energy inputs, but those are hard to replicate and scale. |
The first setup is growing a lot of plants, turning them to charcoal, and burying it. This does require lots of energy, but the plants do it for you. You don't have to input the energy.
The second setup is a process that uses CO2 but doesn't generate fuel, so it needs much less energy than creating hydrocarbons.