The natural source is dominantly the oceans. CO2 concentration has increased because the oceans are warming, and have been since the Little Ice Age and since the last glacial period.
Please discuss the statement above with regard to the 13C isotope data indicating that increasing atmospheric CO2 is predominantly of anthropogenic origin, not oceanic ("natural").
Or as your favorite site http://www.realclimate.org/index.php?p=87 says:
Over the last 150 years, carbon dioxide (CO2) concentrations have risen from 280 to nearly 380 parts per million (ppm). The fact that this is due virtually entirely to human activities is so well established that one rarely sees it questioned. Yet it is quite reasonable to ask how we know this.
They throw around their usual 1/2 science blather and prove nothing except that some part of the increased CO2 is anthro. Now you use the word predominantly, what does that mean exactly? The change in 13C/12C is 0.15% and the increase in CO2 is 21%, so the only way to force a conclusion like "virtually entirely" or your less emphatic "predominantly" is to assume a ridiculously long cycle time for CO2. Your source says 60 years, a "virtually entirely" conclusion requires at least 150 years, but the actual cycle time is 5-6 years. The human part of the increase comes out to about 1/5th or 1/6th.
Sorry, misread your source, they don't give a number for cycle time (or more importantly, for anthro proportion of the increase either).
1. cogitator asks, “Underlined section interpreted as indicating that the observed increase in atmospheric CO2 is not primarily due to anthropogenic sources. Yes or no?” In context, the underlined section is
>>Another AGW tenet is that the buildup of CO2 in the Mauna Loa Record is an accumulation of CO2 throughout the brunt of the industrial era. To make that accumulation viable, AGW advocates claim the duration of CO2 in the atmosphere is a century or more.
>>To the extent that the mean residence time of CO2 is less than a century, THE BUILD UP MUST BE FROM OTHER SOURCES. Others have claimed the residence time is the order of five years or less, and that appears to be supported by their calculations of the total concentration of CO2 in the atmosphere and the flux into the biosphere and especially the ocean. With such short CO2 persistence, the AGW conjecture needs shoring up with a new rationale for the 150 year growth in CO2. Underscore capitalized, http://www.rocketscientistsjournal.com/2006/11/gavin_schmidt_on_the_acquittal.html.
Impliedly, the increase is attributed by AGW peers to industrialization, i.e., is anthropogenic.
Also by implication, cogitator tries to establish a contradiction by relying on the calculated isotopic fraction he discusses next. Proof by rubbing.
2. What is the accuracy in measuring the various isotopes of C and O? Are the errors correlated between different isotopes? What is the sensitivity to temperature? What is the resulting error in the fractions? Without this information, conclusions cannot be drawn from the isotopic data.
Always beware of a parameter calculated as the ratio of noisy variables! They can have very poor characteristics, including instability and divergence. For example and in particular, consider the following:
>>The effective isotopic signatures of various processes calculated by either the Keeling plot approach or theoretically differ widely from the known d13C of the source and are very often indistinguishable in the light of the uncertainties. A back calculation from well distinct fluctuations in pCO2 and d13C to identify their origin using the Keeling plot approach seems not possible. Fischer et al., Use and abuse of Keeling plots in paleoatmospheric research: What can we learn from ±13CO2 in polar ice cores? 4/2/06. http://web.awi-bremerhaven.de/Publications/Fis2006d.pdf
3. You wrote, “This 14C decline cannot be explained by a CO2 source in the terrestrial vegetation or soils.” That still leaves the ocean and subsurface as possible sources, and not just man.
4. All plants do not have the same isotopic carbon preference as implied in your next to last paragraph. Biologists divide the plants into classes called pathways, designated for example as C3 in photosynthesis and C4 for tropical and marsh grasses, with marine processes overlapping.
5. You say, “Indeed, the 13C fractions in the atmosphere and ocean surface waters declined over the past decades. This fits a fossil fuel CO2 source and argues against a dominant oceanic CO2 source.” Is your point the following from the TAR?
>>The amount of carbon dioxide, for example, has increased by more than 30% since pre-industrial times and is still increasing at an unprecedented rate of on average 0.4% per year, mainly due to the combustion of fossil fuels and deforestation. We know that this increase is anthropogenic because the changing isotopic composition of the atmospheric CO2 betrays the fossil origin of the increase.
So what? BTW, is the 30% figure based on ice core data?
First, what is calculated is not the isotopic fraction of the increase, but of samples allegedly representative of the whole CO2 reservoir in the atmosphere.
Second, suppose the entire atmospheric reservoir were replaced by fresh ACO2 in any time period you might choose. What does that have to do with global warming?
Third, why don’t you use the rate of total CO2 increase and the rate of 14C decrease and compute the relative concentration of ACO2 in the atmospheric reservoir? That might be interesting for the carbon cycle, but still irrelevant to global warming.
6. You quote the following
>>The natural source is dominantly the oceans. CO2 concentration has increased because the oceans are warming, and have been since the Little Ice Age and since the last glacial period.
to ask
>>Please discuss the statement above with regard to the 13C isotope data indicating that increasing atmospheric CO2 is predominantly of anthropogenic origin, not oceanic ("natural").
First, as shown in the Acquittal of Carbon Dioxide, during the paleo period the natural source of CO2 was solely the oceans. We assume that the laws of physics are invariant, so it should be true today.
Second, global warming is apparent, and the natural efflux of CO2 from the oceans should be increasing due to an invariant solubility relationship.
Third, I remain skeptical that the data show what you claim, especially without quantifying “predominantly”. You don’t measure the 13C isotope of the increase, but something between a regional concentration and the whole atmospheric reservoir. Where is calculation that takes you from the domain of the measurements to the increase?