Of all the myriad climate skeptic arguments out there, the argument that the current rise in CO2 is not human caused truly is one of the most ridiculous positions one could take.
(Please note, I am not saying it is ridiculous to consider, we should consider everything, but like wondering if the light in the fridge really turns off when you close the door, a quick check with your cell phone video camera really should put it to rest!)
I am closing comments on that thread and directing them here, as surprising as it is to me that there is any need to discuss it!
I’m doing that now because one of our frequent septical visitors is trying to make the case that the CO2 rise is not ours.
It is also an opportunity to use some material that one of AFTIC’s visitors, Doug Mackie, has graciously provided. Doug is a PhD in the Department of Chemistry at the University of Otago in Dunedin, New Zealand. His chemistry degree caught my attention when he responded to another of the more vapid denialist arguments, that CO2 is such a small part of the atmosphere that it can’t possibly have any noticeable effect. I asked him for some good examples of things that are deadly in very tiny concentrations.
Well, it turned out that he is a frequent battler of global warming denial in newspapers and various other venues in New Zeland and so has a few good answers up his sleeve. I will quote below a couple of more specific objections in the “that CO2 ain’t us” meme and Doug’s excellent responses.
Question and Answer 1:
Q: Carbon isotopic ratios indicate that while there is a contribution from the burning of fossil fuels, it is of the order 1-5 percent of the increase in atmospheric CO2.
A: This confusion has to do with residence times and mixing.
Calculating the amount of fossil fuel CO2 in the atmosphere purely from a change in the carbon isotope ratio is not trivial. This is because there is constant natural exchange between the atmosphere, the oceans and the terrestrial biosphere (plants and soil). For example, the famous saw-toothing of the Keeling Curve shows the annual uptake and release of atmospheric CO2 by Northern Hemisphere plants. (There is also a SH effect but as the NH has way more land the effect is more obvious).
(image from Global Warming Art)
Look at AR3WG1 Figure 3.1 . It shows the sizes of each pool and the fluxes between each pool. The oceans contain something like 38,000 Pg of carbon (1 Pg = 1 billion tonnes), the atmosphere about 730 Pg C and the land 2,000 Pg C. However, the natural flux (or exchange) between the atmosphere and the oceans is about 90 Pg C y-1 and between the atmosphere and the land the flux is 120 Pg C y-1. This means that each year 230/730 = 32% of the total CO2 in the atmosphere is exchanged with other reservoirs.
A vital point to note is that it is not the exact same carbon atoms taken up and released (i.e. if they all had serial numbers it would be different ones taken up and released). Thus, the natural flux means that though the total CO2 in the atmosphere is increasing, many of the fossil carbon atoms released to the atmosphere have been swapped and are now in the ocean or in soils/plants.
So it might be technically true (in a Bill Clinton sense) to suggest 1-5% of the individual carbon atoms in the atmosphere at any one time are the exact same carbon atoms released by fossil fuel burning. However, it is the increase in total CO2 that matters in terms of the radiative balance of the atmosphere, not the exact serial number on each carbon atom.
Question and Answer 2:
Q: how do we know the CO2 hasn’t come form the oceans?
A: Since the oceans contain over 50 times more carbon than the atmosphere and soil and plants contain at least twice as much carbon as the atmosphere, ( AR3WG1 Figure 3.1 ), is it possible relatively small changes in either reservoir are responsible for the increase in the atmosphere?
We can be confident the CO2 has come from the oxidation of fossil fuels and has not come from out gassing from the ocean or from soil/land sources by using two key observations.
1) Oxygen decrease
Atmospheric oxygen is going down by the same amount as atmospheric CO2 is going up. Oxygen is so abundant at about 21% that we are in no danger of running out; the change in oxygen simply shows that whatever the source of CO2 in the atmosphere, the carbon part of it has come from the oxidation of reduced carbon compounds and the oxygen has come from oxygen gas in the atmosphere. That is, the extra CO2 was not released in the form of CO2 from an unknown source but instead some reduced carbon compound was burnt in the atmosphere to produce CO2. See: AR3WG1 Section 3.5.1, especially Figure 3.4.
2) Known fossil fuel CO2 emissions.
Most obviously, any alternative explanation for the source of the CO2 in the atmosphere has to also come up with where the 30 billion tonnes of CO2 known to be released by fossil fuel burning each year goes.
Atmospheric CO2 is currently increasing at about 2 ppmv per year (or 16 billion tonnes). That is, only around half of the CO2 we release remains in the atmosphere. The pH decrease in the oceans corresponds to most of the “missing” CO2, so we can also be confident that land use changes etc are not a major source/sink. Caveat: Land use and biomass changes certainly soak up a lot of CO2, some it simply regrowth of forests etc, but the point is that the increasing CO2 in the atmosphere clearly demonstrates that they do not soak up enough.
In summary: (amount of increased CO2 in the atmosphere + the amount of increased CO2 in the oceans) = (amount of known fossil fuel emissions of CO2).
Just how many nails do we need in the coffin before this argument finally stays dead and buried?