Charcoal in soil, also known as Terra preta, Terra preta do Indio, Terra preta nova, Biochar, has proven to have many benefits.
Regarding its reactivty, carbon exists in nature in three functionally different types.
- The type that easily emit energy, as gasoline, crude oil or petroleum gas.
- The type that give away energy only if it is heated, as diamonds (600-800 C), fossil coal (anthracite, 500 C) and charcoal (pyrolysed plant biomass, 300-400 C).
- The type that doesn't react unless energy is added to the molecule, as carbon dioxide
The technical carbon sequestration method,
CCS, (Carbon Capture an Storage) avoids the energetic problem asociated with carbon dioxide by not transforming it at all, just stow it away. Problems associated with this is:
- The process is designed to remove carbon dioxide from high concentration sources, not from ordinary air.
- The concentration and transport of the concentrated gas is very energetically (and economicall) expensive, at least 25% of the energetic (and economic) output of the source
- The carbon dioxide molecule is about three times larger than the carbon (or carbohydrate) molecule (see the picture, where black is the carbon atom, and red is the oxygen), so you can never think of sqeezing it back into the volume of the original source, even with high pressure.
- Since CCS only can be applied at high concentration sources, it can not draw carbon dioxide from orinary air. Thus, CCS can never reduce the carbon dioxide content of the air
To
remove carbon dioxide from the atmosphere, you need to:
- Add energy to evely single carbon dioxide molecule, even at very low concentrations
- Transform them into something that will not let the stored carbon out
- Store it away from the atmosphere for a very long time.
- Do this cheaply, preferrably with some gain.
Plants can do most of this
Charcoal also has a lot of benign effects to the soil:
Terra Preta
Increased metabolism
Today (2008), the carbon dioxide level in the amosphere is about 385 ppm. A relatively safe level is estimated by James Hansen & al. to be less than 350 ppm.
Tipping points
- Complex systems doesn't behave as simple systems.
- They excert sudden changes that not are predictable in time, but foreseeable in type, so called 'tipping points'.
- Examples are:
The amounts
- Currently (2008) the atmpospheric carbon dioxide level is about 285 ppm
- One ppm of carbon dioxide corresponds to about 2.12 Gt carbon.
- Every year, about 8 Gt carbon (as carbon dioxide) is emmited into the atmosphere. Thus, allowing for that some is absorbed by the oceans, the atmospheric content of carbon dioxide increase with 2-3 ppm each year.
- Nobody knows for sure which level that gives the next tipping point.
Emission reductions of any size, even a total stop,
will not reduce the atmospheric carbon content
As carbon dioxide is stable, decrease can only be done by sequestration.
Technical systems (CCS, Carbon capture and storage ) can not sequester carbon dioxide at levels as low as the content of the atmosphere. They require much higher concentrations.
- Besides, to set up a technical system normally require fossil fuels, which emits carbon dioxide
Plants routinely sequester carbon dioide from the atmosphere. Around 300 ppm is their normal operating level.
But plants die, and their carbohydrates will be consumed by microorganisms, returning the carbon dioxide into the atmosphere.
