Uncertainty: The origin of the increase in Atmospheric CO2

One of the ‘Tablets of Stone’ in the argument for ‘Anthropogenic Global Warming’ is that human emission of co2 through the burning of fossil fuel is responsible for the increase in the atmospheric level of this trace gas since pre-industrial times, which now constitutes 0.039% of Earth’s atmosphere. It is claimed that this can be logically deduced and calculated and  there is no doubt we are the guilty species.

But there’s a problem…

One of the central planks of the argument is that we know the sources and sinks of atmospheric co2 well enough to determine the proportion that belongs to us. Another is that the changing ratio of two isotopes of carbon (d13 and d12) is a ‘fingerprint’ of human emission. Another is that the ratio of Oxygen to CO2 is consistent with combustion estimates. But what about volcanoes?  These are not thought by the proponents of the AGW argument to figure largely in the carbon cycle on an annual basis. As Ferdinand Engelbeen put it on a recent WUWT thread ‘Dusting for Fingerprints in the Holocene‘:

There is little doubt left that humans are entirely responsible for the d13C decline (and the CO2 increase). Other sources are too high in d13C (volcanoes, carbonate rock weathering) and too small in emissions. Most of all natural CO2 is around zero per mil d13C: that is all inorganic carbon (carbonate -rock- layers from plankton shells), sclero sponges, corals,… That is also the case for the inorganic carbonates dissolved in the (deep) oceans and ocean sediments, therefore also for volcanic CO2 from subduction volcanoes.

Ferdi is a competent and honest researcher, and a pleasant and easy person to talk to about this issue. But when I tried to point up some new research linked on a website I’ve been reading, my comment got deleted. So I’ll raise it again now. The website in question is that of consulting geologist Timothy Casey. In his article on Volcanic Carbon Dioxide he has this to say:

A brief survey of the literature concerning volcanogenic carbon dioxide emission finds that estimates of subaerial emission totals fail to account for the diversity of volcanic emissions and are unprepared for individual outliers that dominate known volcanic emissions. Deepening the apparent mystery of total volcanogenic CO2 emission, there is no magic fingerprint with which to identify industrially produced CO2 as there is insufficient data to distinguish the effects of volcanic CO2 from fossil fuel CO2 in the atmosphere. Molar ratios of O2 consumed to CO2 produced are, moreover, of little use due to the abundance of processes (eg. weathering, corrosion, etc) other than volcanic CO2 emission and fossil fuel consumption that are, to date, unquantified. Furthermore, the discovery of a surprising number of submarine volcanoes highlights the underestimation of global volcanism and provides a loose basis for an estimate that may partly explain ocean acidification and rising atmospheric carbon dioxide levels observed last century, as well as shedding much needed light on intensified polar spring melts. Based on this brief literature survey, we may conclude that volcanic CO2 emissions are much higher than previously estimated, and as volcanic CO2 contributions are effectively indistinguishable from industrial CO2 contributions, we cannot glibly assume that the increase of atmospheric CO2 is exclusively anthropogenic.”

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“It seems that Gerlach (2011) drew his interpretation from a preference for the “global” “magmatic” carbon dioxide emission estimate of Marty and Tolstikhin (1998) which was devoloped from the generalisation of isotope ratios across provinces of varied geochemistry. This multimodal generalisation, as I have shown in the example of Laki (Section 2, above), can be spectacularly inaccurate. Gerlach reports this figure in the following contrastive statement:

“The projected 2010 anthropogenic CO2 emission rate of 35 gigatons per year is 135 times greater than the 0.26-gigaton- per-year preferred estimate for volcanoes.”

In the units I am using here, that translates to a “preferred” estimate of worldwide volcanic carbon emission at 0.071 GtCpa. At this point, I think it worth contrasting this with a quote from Cardellini et al. (2011) who are actually engaged in some real research:

“Quantitative estimates provided a regional CO2 flux of about 9 Gt/y affecting the region (62000 km2), an amount globally relevant, being ~ 10% of the present-day global CO2 discharge from subaerial volcanoes.”

That 9GtCO2pa translates to 2.45 GtCpa for just one region, which is more than 34 times the latest personally “preferred” “global” estimate offered by Gerlach (2011). One may well be keen to ask how it is possible that anyone would prefer to propagate a “global” estimate which is almost 35 times smaller than only one of the many provincial figures that must be summed in order to arrive at a worldwide estimate in the first place?

So the empirical evidence from Cardellini et al has the ‘preferred estimate’ of worldwide emission of co2 from volcanic sources in big trouble. But what about the isotope argument? Ferdi Engelbeen is sure that volcanic  sources of co2 are  too high in the lighter isotope d13C to account for the falling ratio. But if the ‘preferred estimate’ is itself derived from isotope ratios, then since annual emission of co2 from volcanic sources may be  equivalent to or higher than emission from human sources as the empirical work of Cardellini et al shows, the falling isotope ratio and oxygen ratio argument’s calculations are thrown into uncertainty,  and another AGW ‘Tablet of Stone’ is shattered.

This then is good reason to remind ourselves of the work of Murry Salby, the Chair of Climate Science at Macquarie University.  Joanne Nova tells us He’s held visiting professorships at Paris, Stockholm, Jerusalem, and Kyoto, and he’s spent time at the Bureau of Meterology in Australia. If you are not already familiar with Salby’s work, visit the link to the video presentation he gave to the Sydney Institute, which is well worth watching.

Ferdi comments on that Jo-Nova thread:

That humans are the cause is quite sure:
– The mass balance: It is impossible that nature was a net contibutor to the increase, because the measured increase is less than the emissions. Thus nature was a net sink for CO2 over the past at least 50 years.

I think that in the light of the evidence from Cardinelli et al (whose work is only available as an abstract from the EGU proceedings so far), this whole line of argument needs reconsidering. If we managed to miss 90 Gigatons of emission from volcanic lava in our estimates, then our knowledge of the carbon cycle is woefully lacking. Sinks are obviously much bigger than previously estimated too, and human emission is an even smaller part of the overall carbon cycle than the 5% previously believed.

Ferdi’s argument above only makes sense if the isotope ratio argument holds too, otherwise the increase in atmospheric co2 could quite easily be due to some natural balance shift between sources and sinks which has nothing to do with human emission. But Murry Salby. Timothy Casey and Cardellini et al have strong evidence that the isotope ratio argument is false.

The cracks in the Anthropogenic Global Warming argument are getting wider.

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Cardellini, C., Chiodini, G., Caliro, S., Frondini, F., Avino, R., Baldini, A., & Donnini, M., 2011, “CO2 fluxes from Earth degassing in Italy”, Geophysical Research Abstracts, Vol. 13, EGU2011-7778-1. http://meetingorganizer.copernicus.org/EGU2011/EGU2011-7778-1.pdf

No ‘it’s’ were used in the making of this post. 🙂