Atmospheric CO2.

By Pat Hackett

How much has CO2 risen in our atmosphere due to anthropogenic (the result of human activity) causes? This question is quite straightforward to arrive at a reasonable estimate but it is interesting to see the attempts to arrive at quite meaningless and far off estimates. This flawed method here is one by T.V. Segalstad who ignores the effects of fluxes of carbon between the oceans, biosphere and atmosphere when looking at carbon isotopes in the atmosphere.

However first some basic facts:- 

Changes in CO2 from preindustrial times to 2014.

Pre industrial CO2 levels had been relatively stable for several hundred years at around 280ppm and have risen since then to around 400ppm. Accurate measurements for over 50 years form sites such as Mauna Loa show the increases since 1956. (figure 1)

Figure 1:- Increase in CO2.

Figure 1 shows the net annual variation in CO2 due to exchange of CO2 between the atmosphere and mainly the biosphere which, over a single year, is much greater than the annual but steady increase in CO2 due to anthropogenic emissions. This annual cyclic variation can be attributed mainly to the growth and decay of organic matter in the Northern Hemisphere.

Unless volcanic activity has increased by something in the order of 50 fold, waiting for the industrial revolution to start doing so, it is reasonable to assume that the steady increase has been due to anthropogenic causes. 120ppm out of 400ppm represents 30% due to anthropogenic causes

.

How can a reasonable estimate of around 30% be changed to a range of estimates from somewhere between 0 and 4%? You may stumble across statements like this in some web sites.

Here is a link that deals with the following issue:- The Amount of Non-Fossil-Fuel CO2 in the Atmosphere-

http://www.co2web.info/hawaii.pdf

 and thus T V Segalstad arrives at the following conclusion:-

"At least 96% of the current atmospheric CO2 comes from non-fossil-fuel sources."

Does this address the same question as:-

How much has CO2 risen in our atmosphere due to anthropogenic causes?

T V Segalstad would like you to think so and numerous other web sites/blogs by the same author and others use the confusion to make further flawed conclusions. For example:-

“Hence for the atmospheric CO2 budget marine degassing and juvenile degassing from e.g. volcanic sources must be much more important, and burning of fossil-fuel and biogenic materials much less important, than hitherto assumed”.

This later cautiously worded conclusion follows on from a misinterpretation of the first conclusion.  The first conclusion (At least 96% of the current atmospheric CO2 comes from non-fossil-fuel sources.) in the above article may or may not be accurate. That is not the issue that I take up here, however it may appear to lead to the (false) conclusion that our atmosphere has only risen by 4% due to anthropogenic causes.

The flawed argument.

First an analogy.

A bank note analogy:-

Imagine you deposited £100 notes in your bank and went back a week later to withdraw your money and the cashier apologized and said only £4 of your original notes were left in your branch of the bank so you can only withdraw £4.

Surely this is not the mistake the author makes with the distractions of using the science of carbon isotopes ratios? Yes the analogy is incredibly quite similar and yet with this mistake, and a few others on the way, other false conclusions regarding the half life of CO2 in the atmosphere and the % contribution of CO2 to the greenhouse effect are then obtained. The confusion and false conclusions are carried forward to another article by the same author, and can be read in the following link.

http://www.co2web.info/

Pre industrial global carbon reservoirs.

These are given in figure 2 below. The main point here is that the reservoirs in the biosphere and the oceans are much greater than the atmospheric reservoir.

Figure 2:- Global carbon reservoirs.

The short term carbon cycle.

The short term carbon cycle deals with the movement of carbon between the atmosphere, the ocean and the biosphere. (The long term carbon cycle concerns the movement of carbon from volcanic activity as a source and the sinking of carbon by both weathering of rocks and the smaller but significant burial of organic carbon).

Figure 3:-  Pre industrial carbon.

Exchange of carbon between the atmosphere and the biosphere and oceans is continual and daily which is many times greater than the additional rate of CO2 from fossil fuels over a single year.  This exchange is partly indicated by the net annual cyclic variations that you can observe in figure1 above. However in relatively equilibrium conditions (without the burning of fossil fuels) the net flow is on average zero. Although this is never exactly the case, the approximation to this in pre-industrial times would have been much closer to this as it is in post-industrial times.

Figure 4:- carbon 2014.

When comparing the reservoirs of carbon from pre-industrial to present day levels, figures 3 and 4, it is clear that the atmosphere has gained considerable carbon (in the form of CO2). During this time there has been considerable exchange of carbon into and out of the atmosphere, to and from the biosphere and the oceans, as is always the case. However there will also be a net movement of carbon into the biosphere and the oceans during this time due to the higher CO2 pressure in the atmosphere.

Which molecules stay in the atmosphere?

There is a slight difference in the ratio of carbon isotopes from fossil fuels compared with that from the other sources. However since the ocean and biosphere reservoirs are much bigger than the atmosphere reservoir, this difference in ratio will be much diluted with the continual interchange of carbon between these reservoirs. (This is useful for genuine scientific research in gaining further knowledge about the short term carbon cycle. An explanation of using C13:C12 isotope ratios can be read here ).

The claim “At least 96% of the current atmospheric CO2 comes from non-fossil-fuel sources” merely focuses on which molecules (identified from the ratio of carbon isotopes) are presently in the atmosphere and not how these ratios changed over time.

The C13/C12 ratio has been falling at a slower rate than would be the case if there was no exchange between the atmosphere and in particular the ocean. This should come as no surprise when the exchange is considered but it is this that Segastald has ignored.

For the purpose of deciding “How much has CO2 risen in our atmosphere due to anthropogenic causes”, it should be clear that focusing on which molecules are presently in the atmosphere does in fact not address that question (This is similar to the analogy with the bank notes described above). However, the false claim makes out that it does, with the pseudo science of playing with the data of carbon isotopes. Then with the use of that false connection, further false conclusions are made about the lifetime of CO2 in the atmosphere.

Where has the extra CO2 come from?

T V Segalstad suggests that the increase in CO2 as shown in figure 1 above has come more from “marine degassing and juvenile degassing from e.g. volcanic sources” and not from burning of fossil fuels.

Marine degassing.

If the extra CO2 has come from increasing marine degassing then the oceans must have been warming at a faster rate than claimed in many reports from climate scientists. I don’t think the author would particularly likely you to reach this conclusion, but otherwise how would the oceans start to have a net movement of CO2 into the atmosphere and what could have caused this warming? It further leaves the question where has all the anthropogenic emissions gone? This degassing, however, is not consistent with the levels of ocean pH that has been falling but rather it would require the reverse. It seems that this degassing of CO2 from the oceans is not a reasonable explanation that fits with the evidence.

Volcanic sources.

I think it is beyond all statistical belief to think that volcanic activity has been increasing at the rate equivalent to the rates and timing of anthropogenic production since the industrial revolution. Furthermore the increase in lighter carbon in the atmosphere would require this new coincidental volcanic activity to be coming from the mantle. (The mantle is believed to have a slightly larger percentage of lighter carbon).  However this grasping at straws is not uncommon.