Part of the reason why I took such a dim view of the nonsense discussed in Dimonomics is that so little is known about the carbon cycle, and so little of what is known is understood. Political posers hawk policies that elevate their power, claiming that they are justified by allusions to carbon.

What is factual is that humans emit a variety of carbon gasses, and their atmospheric concentrations have increased. But until recently we couldn't make the connection empirically.

Using data from the SCIAMACHY instrument aboard ESA's Envisat environmental satellite, scientists have for the first time detected regionally elevated atmospheric carbon dioxide – the most important greenhouse gas that contributes to global warming – originating from manmade emissions. . .

Dr Michael Buchwitz from the Institute of Environmental Physics (IUP) at the University of Bremen in Germany and his colleagues detected the relatively weak atmospheric CO2 signal arising from regional ‘anthropogenic’, or manmade, CO2 emissions over Europe by processing and analysing SCIAMACHY data from 2003 to 2005.

"The natural CO2 fluxes between the atmosphere and the Earth’s surface are typically much larger than the CO2 fluxes arising from manmade CO2 emissions, making the detection of regional anthropogenic CO2 emission signals quite difficult," Buchwitz explained. . .

"We know that about half of the CO2 emitted by mankind each year is taken up by natural sinks on land and in the oceans. We do not know, however, where exactly these important sinks are and to what extent they take up the CO2 we are emitting, i.e., how strong they are.

"We also don’t know how these sinks will respond to a changing climate. It is even possible that some of these sinks will saturate or turn into a CO2 source in the future.

And the reverse. Some sinks could draw down more as growing conditions improve, and new sinks could arise. It's likely that all of these things will happen and we have no idea what the net effect will be. Changes in related factors, such as increased availability of some nutrients such as mineral nitrogen, could have large effects.

The idea of seeking to sequester carbon - such as by making and using biochar - has an attractive symmetry: we could sequester amounts equal to what we emit from fossil fuels and so have no net effect on atmospheric concentrations. But how good is it? How long does the carbon stay sequestered? We have few clues.

There is no doubt that in certain environments, charcoal is indeed recalcitrant. In a study of marine sediments in the North Pacific Basin, Herring (1985) found that “charcoal in the marine sediment is stable for several tens of millions of years” and that “charcoal forms a large percentage of the carbon content in the sediments”. Large accumulations of charred material with residence times in excess of 1000 years have also been found in soil profiles (Forbes et al 2006, Glaser et al 2001, Saldarriaga, et al 1986). Glaser et al (2003) attribute the presence of large stocks of pyrogenic black carbon in Amazonian dark earths, several hundred years after the cessation of activities that added it to the soil, to its chemical recalcitrance. Also, 14C ages of black carbon of 1000 to 1500 years from Amazonian Dark Earths suggest that it is highly stable (Glaser, 1999). Deposits of charcoal up to 9500 have been found in wet tropical forest soils in Guyana (Hammond et al, 2007), up to 6000 years old in Amazonia (Soubies 1979), and up to 23,000 years old in Costa Rica (Titiz & Sanford, 2007).

The conclusion that BC is long-lived is supported by Bird and Gröcke (1997) who found that a component of charred material is highly oxidation resistant under laboratory treatment both with acid dichromate and basic peroxide. The fraction of biochar that will exhibit such oxidation resistance will of course depend upon both the feedstock and pyrolysis conditions.

But the books don't balance.

Masiello (2004) argues that there must be some, as yet unknown, large scale loss process for black carbon. Firstly, there is a discrepancy between known rates of black carbon production and loss. Kuhlbusch (1995) estimates annual BC production to be 0.05-0.27 Gt/year. The rate at which organic carbon is deposited to the sea floor on the other hand is estimated at 0.16 Gt/year (Hedges & Keil, 1995). According to Masiello (2004), “the only documented loss process for BC is deposition in ocean sediments”. This implies, according to Masiello, that BC should account for at least 30% of sedimentary organic carbon, whereas it is only observed to provide about 3 – 10%. Furthermore, at least some of this sedimentary BC is thought to come from petrogenic graphite adding to the discrepancy between terrestrial rates of production and sedimentary loss of BC.

So, if BC is not being removed from the soil as fast as it is being produced, might it simply be accumulating there? According to Masiello (2004), this possibility is also ruled out by a calculation of how much BC there would be in the soil organic carbon pool assuming it had been produced at current rates since the last glacial maximum. Masiello (2004) calculates that this would imply between 25 – 125% of total soil organic carbon would be BC which, Masiello (2004) states, is implausibly high even if we take the lower limit and account for losses by erosion.

We find really old stuff, but not enough to convince us that there are not mechanisms that cycle it back to the atmosphere. Maybe the calculations and assumptions are flawed and the char is all still there? Maybe a lot is destroyed by known mechanisms such as fire? Charcoal burns nicely. If some is made by a forest fire, it might be consumed by the next fire unless it is somehow moved below ground, out of harm's way. Maybe there are chemical or microbial means of recycling carbon that we don't yet know about?

When your hear strident calls for policies and behavior changes remember that these folks have no idea what's really going on with carbon on a global scale over time. It's just business. They are selling. Maybe you will buy and so give them power or money or some other valued asset because you are entertained, or afraid or just like the polcies for other reasons unrelated to carbon or climate. Most are, after all, exactly the same policies advocated for decades by various totalitarian ideologies.

It is also well to remember that carbon isn't all there is to climate. The soot angle discussed in ABCs is as much about albedo changes as aerosols. And there are lots of other albedo changes we have made to the planet as we use an increasing percentage of the surface, in increasingly intense ways.

You can make a solid argument for increasing carbon in soils for agronomic benefit. Both organic carbon that will fairly quickly decompose back into atmospheric carbon, and char, are beneficial soil amendments that improve productivity and reduce other inputs such as nutrients and water. If such things were done widely and with vigor the rough calculations indicate that fossil emissions could be negated, but it is worth doing even if those emissions are not really a concern to any except those in the carbon business.