NOTE: This post is the second in the series from Dr. Roy Spencer of the National Space Science and Technology Center at University of Alabama, Huntsville. The first, made last Friday, was called Atmospheric CO2 Increases: Could the Ocean, Rather Than Mankind, Be the Reason?
Due to the high interest and debate his first post has generated, Dr. Spencer asked me to make this second one, and I’m happy to oblige.
Here is part2 of Dr. Spencer’s essay on CO2 without any editing or commentary on my part.
(Side note: Previously, I erroneously reported that Dr. Spencer was out of the country. Not so. That was my mistake and a confusion with an email autoresponse from another person named “Roy”. Hence this new update.)
More CO2 Peculiarities: The C13/C12 Isotope Ratio
Roy W. Spencer
January 28, 2008
In my previous post, I showed evidence for the possibility that there is a natural component to the rise in concentration of CO2 in the atmosphere. Briefly, the inter-annual co-variability in Southern Hemisphere SST and Mauna Loa CO2 was more than large enough to explain the long-term trend in CO2. Of course, some portion of the Mauna Loa increase must be anthropogenic, but it is not clear that it is entirely so.
Well, now I’m going to provide what appears to be further evidence that there could be a substantial natural source of the long-term increase in CO2.
One of the purported signatures of anthropogenic CO2 is the carbon isotope ratio, C13/C12. The “natural” C13 content of CO2 is just over 1.1%. In contrast, the C13 content of the CO2 produced by burning of fossil fuels is claimed to be slightly smaller – just under 1.1%.
The concentration of C13 isn’t reported directly, it is given as “dC13”, which is computed as:
“dC13 = 1000* {([C13/C12]sample / [C13/C12]std ) – 1
The plot of the monthly averages of this index from Mauna Loa is shown in Fig. 1.
Now, as we burn fossil fuels, the ratio of C13 to C12 is going down. From what I can find digging around on the Internet, some people think this is the signature of anthropogenic emissions. But if you examine the above equation, you will see that the C13 index that is reported can go down not only from decreasing C13 content, but also from an increasing C12 content (the other 98.9% of the CO2).
If we convert the data in Fig. 1 into C13 content, we find that the C13 content of the atmosphere is increasing (Fig. 2).
So, as the CO2 content of the atmosphere has increased, so has the C13 content…which, of course, makes sense when one realizes that fossil-fuel CO2 has only very slightly less C13 than “natural” CO2 (about 2.6% less in relative terms). If you add more CO2, whether from a natural or anthropogenic source, you are going to add more C13.
The question is: how does the rate of increase in C13 compare to the CO2 increase from natural versus anthropogenic sources?
First, lets look at the C13 versus C12 for the linear trend portion of these data (Fig. 3).
The slope of this line (1.0952%) represents the ratio of C13 variability to C12 variability associated with the trend signals. When we compare this to what is to be expected from pure fossil CO2 (1.0945%), it is very close indeed: 97.5% of the way from “natural” C13 content (1.12372%) to the fossil content.
At this point, one might say, “There it is! The anthropogenic signal!”. But, alas, the story doesn’t end there.
If we remove the trend from the data to look at the inter-annual signals in CO2 and C13, we get the curves shown in Figures 4 and 5.
Note the strong similarity – the C13 variations very closely follow the C12 variations, which again (as in my previous post) are related to SST variations (e.g. the strong signal during the 1997-98 El Nino event).
Now, when we look at the ratio of these inter-annual signals like we did from the trends in Fig. 3, we get the relationship seen in Fig. 6.
Significantly, note that the ratio of C13 variability to CO2 variability is EXACTLY THE SAME as that seen in the trends!
BOTTOM LINE: If the C13/C12 relationship during NATURAL inter-annual variability is the same as that found for the trends, how can people claim that the trend signal is MANMADE??
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My mind is trying to bend around the discussion.
From this layman’s view, I wonder if the temp-atmosphere-ocean-CO2 venting-anthro-uptake-input. etc. has a “Chicken or Egg” quality about it? Sorry I can’t be more specific.
Good threads Anthony!
Jd
Well, using the Everyday Math approach, I suggest froming a team and cutting out pictures of farm animals and pasting them in a notebook and downloading a report on cruelty of the methods of modern dairies.
(And then protect the endangered fox when he gets into chicken COOP-A.)
Tim and Evan,
The 13C/12C ratio is decreasing, as well as in the atmosphere as in the upper oceans, over about 150 years, since mankind is using fossil fuels in increasingly amounts.
This excludes the oceans as large (continuous) source of extra CO2, as ocean CO2 has a 13C/12C ratio of about zero to slightly positive (0-4 per mil) d13C, that means a higher ratio 13C/12C than the atmosphere which is currently around -8 per mil.
With more CO2 from the oceans, the positive d13C would increase the d13C from the atmosphere with some amount per year, e.g from -8 per mil to -7.9 per mil d13C. But we see that the opposite happens, even during stronger outgassing of the oceans during the warm El Niño episodes. Despite the stronger outgassing, the emissions still are more influential, as the emissions have a much lower 13C/12C ratio (-24 per mil d13C) than the atmosphere.
Thus what we see in the d13C record, is that there is a continuous decrease of d13C levels in the atmosphere and upper ocean levels, caused by human emissions, but a small variability in the year-by-year decrease, caused by (mainly ocean) temperature changes. See:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/sponges.gif
About the same happens with the increase of total CO2 in the atmosphere: the increase is mainly caused by human emissions, but the increase speed is modulated by temperature variations.
If we look at only the variability of the increase/decrease speed, then we see large variations from year to year, but in the total trend (over the past 50/150/600 years), these are tiny wobbles…
I find this a very intersting and stimulating discussion. Thank you, Roy Spencer for posting the essay and thank you to the other contributors. It’s provoking me to give some serious thought to the problem of the carbon system and isotopes.
At this stage, I just want to make one point concerning the carbon dioxide-aqueous carbon dioxide-bicarbonate-carbonate system. Comments have been made that the deep ocean cannot be a source of isotopically depleted carbon dioxide because the carbon-13 compositions are close to 0 per mille wrt to VPDB (VPDB is the standard to which carbon isotope compositions are referred).
Most of the carbon in the ocean is in the form of bicarbonate and not aqueous carbon dioxide. There is a marked fractionation between carbon dioxide and dissolved bicarbonate, with the carbon dioxide in equilibrium with bicarbonate being some 8 to 10 per mille depleted in 13C with respect to the bicarbonate. This is temperature dependent, with the degree of fractionation decreasing with increasing temperature.
One might expect that CO2 degassing from the ocean would have isotope composition close to -8 per mille and not close to 0 per mille as has been suggested by some correspondents here.
At least that’s my take on the problem at first sight!
I think Dr. Spencer is on the right track. There is no doubt that ocean uptake and outgassing are temperature dependent. The big problem is trying to get accurate estimates on the details of these processes, which last I heard was not a trivial problem.
As for the anthropogenic signal in the C13/C12 ratios there is one other thing to consider.
Since increased C02 is thought to increase plant biomass, and higher temperatures also are conducive to plant growth, it is entirely possible that the decreasing C13/C12 ratio is the result of increased decay of photosynthesizing organisms, which is secondary to increased productivity.
This is not to say that there isn’t a fossil fuel component, but it will be hard to find amongst the huge natural fluxes.
Fascinating discussion! Thanks to Anthony and Dr. Spencer.
This is the type of open debate of climate fundamentals that is unavailable at most climate sites. It should be required reading for all students of atmospheric sciences, marine science, climatology, geology, and meteorology.
I can follow the arguments but the numbers just don’t add up for me.
Humans are adding CO2. This CO2 is going somewhere. If humans were not adding the CO2 then the CO2 level would not rise as fast or might even fall assuming that the natural sources and sinks are not responding to human emissions.
To let humans off the hook one would have to argue that nature tightly regulates the levels of CO2 in the atomosphere and that the natural sources would increase (or sinks decrease) to replace whatever CO2 humans add.
It seems to me that this investigation should start by looking for evidence that the CO2 levels are tightly regulated by nature. If they are regulated then the isotope ratio becomes irrelevant. If they aren’t regulated then the human contribution will add to the total no matter what nature is doing on its own.
Paul Dennis,
Thanks for your thoughts. What you say about the bicarbonate / CO2aq fractionation is very interesting.
I did give up to understand why there was a (preindustrial) d13C equilibrium between the oceans and atmosphere, where the oceans were average at 0 to +5 per mille, while the atmosphere was near continuously at -6.4 per mille.
Have you more literature info about that?
Great discussion. If greater amounts of atmospheric CO2 increase plant growth, and present CO2 concentrations should increase growth 20-30%, shouldn’t the bi-annual minima and maxima of measured CO2 be more divergent?
As a COMPLETE layman, I appreciate the fact that there is a level of scientific detail way beyond me that is necessary for the community to debate. I know nothing of C12 ratios and all that, so I can’t comment on it. I also understand that this post is intended to debate the scientific merits of Dr. Spencers paper, and not a debate over the general AGW merits. However, after my disclaimer, I cannot reconcile the basic facts, which don’t seem to be debated here or elsewhere: (1) it is temerature that is driving the oceanic exchange of CO2 levels, not vice-versa. If it were vice-versa, and CO2 drives temperature, and given the HUGE reservoir of CO2 in the oceans, we would have an unstable system, and run-away temperature increases; and (2) the annual or seasonal temperature variation and SST variation causes CO2 exchange on a level that dwarfs human contributions.
If a warmer ocean releases huge amounts of CO2 into the atmosphere, which does NOT result in the cascading effect (or positive feedback) of driving the temperatures even higher, then how can our small contribution drive the temperature high enough to cause a global catastrophe? The only way that would happen is if the carbon cycle is so finely tuned and so highly sensitive, that any external carbon inputs to the system would cause it to go unstable. And I find that extremely unlikely, since we know that external inputs, such as major volcanic activity, war, fires, etc., have occurred many times throughout history, even recently. There had to have been spikes in the atmosheric CO2 levels that were beyond this delicately balanced carbon cycle.
Therefore, if both (1) and (2) are true, then catastrophic AGW cannot be true. My questions, then, are this: are (1) and (2) still a point of debate within the community? Where is my logic flawed?
I apologize if this is too far off topic, but I just can’t absorb the details until I get past the basics.
E Mohr,
You are right that there is more decay with higher temperatures, as good as there may be more uptake. But the oxygen balance shows that currently there is about 1.5 GtC more uptake than decay of vegetation over a year. Thus despite the huge seasonal flows, there is no net addition of CO2 from vegetation to the atmosphere and a net increase of 13C, as 12C is preferentially built into vegetation.
Ferdinand Engelbeen wrote:
“while current wood shows 14C/12C ratios more or less equal to the current atmospheric level.”
If plants preferentially uptake the lighter carbon isotope in the C12/C13 balance why is the C12/C14 ratio about the same in current wood and current atmosphere? Surely the C14 in wood should be deficient compared to the atmosphere?
MAJOR REVISIONS TO MY ORIGINAL POST:
This is what happens when one tries to do science in real time….
I went back and redid how I get the “trend” (I now use a 2nd order polynomial), and I switched to the traditional way of computing the annual cycle. I’m now sure I am doing the best that can be done to separate out the low frequency, seasonal cycle, and interannual variability signals.
I don’t want to spill ALL the beans because it’s clearly time to write up something to submit for publication. But, basically, each of the three time scales have their own, distinct values of dC13 at each of 3 stations: Mauna Loa, Barrow, and South Pole.
As a teaser, the seasonal cycles at Mauna Loa and Barrow, Alaska have a 100% terrestrial biomass and/or fossil fuel signal (-26.6 and -26.4 permil, respectively). No surprise there.
The dC13 values for the TRENDS for those two stations are MUCH less than the terrestrial/fossil signal…more like an oceanic signal.
And, finally, the trend signal at the South Pole has a dC13 value of only -1.6. That is very close to the Pee Dee Belemnite standard for “natural” CO2 devoid of marine or terrestrial depleted-C13 influences (if there is such a thing), which is by definition, 0.0.
Interesting stuff.
Following the thread with great interest, but, like many another, with a much lower level of real understanding.
I admire the spirited, yet reasoned (and source-attributed) nature of these discussions. This is real, collegial sparring of the highest quality. And, needless to say, rarely observed elsewhere.
Keep up the good work. You are a great example for young science types.
Dear Dr. Spencer,
Can you update the graphs according to your revisions?
I can’t place your remark about the (25-years?) trends, as there is little difference for d13C trends between Barrow and the South Pole, but there is an altitude delay (Barrow 7 m, Mauna Loa 3000 m) and a NH-SH delay.
And Barrow and Alert show a much deeper decrease around 1990 than the other stations. See:
http://www.ferdinand-engelbeen.be/klimaat/klim_img/d13c_trends.jpg
The lag between NH and SH (as well as for CO2 as for d13C trends) points to a NH source of d13C depleted extra CO2…
And one need to take into account the large seasonal ocean circulation (about 90 GtC/yr) which dilutes the d13C signal…
This is real, collegial sparring of the highest quality. And, needless to say, rarely observed elsewhere.
My level of understanding is probably less than yours, Wayne, but it is a refreshing change from the Hockey team, isn’t it? Now if only my math and physics skills were a little sharper.
For TR.
Sorry I don’t have any links to relevant papers, but a quick google search should find the info for you. Anyway if memory serves, regarding point 1. The ice core data shows that there is a lag between temperature change and [CO2]. This varies from ~ 600 years to as much as ~2300 years, and it is always the case that temperature changes first and this is followed by a change in [C02]. Therefore it seems that dT drives [CO2]. Certainly the CO2 solubility versus temperature graphs tell us that this is so.
As for point 2, the seasonal changes definitely dwarf the proposed human contribution. Judging by the large jumps in atmospheric [CO2] during El Nino events, it is tempting to think that this is SST driven, especially considering CO2 solubility is reduced in warm water.
Meanwhile for Ferdinand, you have some very interesting graphs on your web site that I will have to think about. Zeer interesant.
BTW my old Geochemistry Text (Brownlow, 1979) – no doubt outdated – shows large inflows of inorganic ocean carbon going into biomass – presumably photosynthetic plankton and other marine species. My thought was that, if the oceans have become more productive this would increase total biomass, and also the total organic flux, which might explain some of the decrease in d13/d12 ratios. It’s interesting that the sponge data shows a steady decline in d13 that coincides with the end of the little ice age, and predates large human emissions. On the other hand I have no idea why the sponge data showed essentially steady d13/12 ratios before 1850. Perhaps less intensive farming and fertilizer effluent into the ocean, or something else. I’m looking forward to Dr. Spencer’s paper and his ideas on this.
All in all really great data and food for thought.
Mike Borgelt,
I suppose that the 14C/12C ratio is less affected by biological uptake processes, as the amount of 14C in the atmosphere is extremely small (some 10^-12), compared to the 13C, which is about 1%. Thus any 14CO2 which passes by might be incorporated in the carbon cycle of vegetation.
Anyway, this is what I learned from several sources, including the following (slide 26 in the slide show mentioned below):
E. Mohr,
It is the other way out: more ocean productivity uses primarely more 12C, thus leaving more 13C behind in the upper oceans. This makes that the upper oceans are 1-4 per mil higher in d13C than the deep oceans, the highest values are found at places with the highest production…
The about 1°C change between MWP – LIA only gives a small d13C change, the opposite temperature change LIA-current supposedly is not larger. Thus the bulk of the reduction is from fossil fuel burning…
The idea about a strong oceanic component in the present co2 rise is, as far as i know, hardly a brand new hypothesis, but a rather dead horse being pulled from its grave every now and then – by Khilyuk& Chilingar, Howard Hayden, Zbigniew Jaworowski & Segalstad from Lyndon LaRouches “Schiller Institute”, by E.G.Beck and now by Dr. Spencer.
I have not seen anything new in Spencers post that has not been quite thoroughly debunked or otherwise done to death elsewhere, and I think Ferdinand Engelbeen has made a clear and eloquent presentation pointing the usual arguments out – applause.
I would like to ask a further, quite simple question (sorry if this has been adressed somewhere I have not read carefully enough): Even leaving the isotopic signal aside, how can Spencer defend his hypothesis when it has been shown very clearly that the ocean is a huge net sink of anthropogenic co2?
E.g. by Sabine et al (Science July 2004): http://www.gfdl.noaa.gov/reference/bibliography/2004/cls0401.pdf
or Sarmiento et al. (Nature May 1998)
http://www.nature.com/nature/journal/v393/n6682/abs/393245a0.html
???
Nobody disputes that manmade co2 is but a small part of the total carbon flux, and neither do I think that anybody disagrees with the notion that there is a huge exchange back and forth between the atmosphere and the ocean´s upper layers, nor with the daily and seasonal variations of co2. But when all this is taken together and accounted for, the bottomline seems to conclude that the oceans have had a net uptake of more than 100 billion metric tonnes since the Industrial Revolution. This taken together with the fact that the deep oceans are indeed lagging the upper layers in co2 uptake hardly supports any hypotheses about a deep-ocean source, and when the isotopic evidence is further added upon, I frankly do not see any shred of evidence to back up Dr. Spencers claims?
It does seem like Spencer really honestly believes he is on to something that everyone else has so far missed, and I am open to the possibility that there is something I have myself missed (both here and back at ecology on the undergraduate level).
However, as I read this and most of the comments, it appears to me as if Dr. Spencer simply has not really bothered to study much of the rich literature on this subject before doing his calculations and writing this here up.
Well, I mentioned very early on (in the previous thread) that the DoE lists the oceans as a net sink (around minus 2 BMTC/year).
But would seem to be the very point that Dr. Spenser is disputing.
That would leave the question as to where man’s 6.3 BMTC is winding up (it goes to atmosphere and from there 3.2 goes to land and/or sea sinks).
So if the ocean is net a contributor, that would have to mean that the land is absorbing it all, c. 3%+ more exchange than measured, and the ocean exchange measurements is off by at least 6%.
Or else the ocean is absorbing some but exuding that much more and then some.
Either that or man’s 6.3 BMTC output number would have to be wrong.
Assuming the base numbers are right. Could the measurements be that far off?
Loquor,
I had Ecology too but I think my physics, math and chemistry prepared me better for this study. You didn’t mention why you think the deep ocean is lagging in CO2 uptake, but in any event, Dr. Spencer is simply stating that one particular argument in support of AGW is invalid. You haven’t addressed that issue and the remainder of your discussion does not seem to pertain.
Evan,
There is one other possibility: that size of the sinks depends on the amount of CO2 added. In other words, if man was not emitting the CO2 the ocean would contribute more because the planet is trying to get to some new CO2 equilibrium point and would do that no matter what humans do.
If that hypothesis can be supported by the evidence then isotope ratios are irrelevant.
I’m sorry, it would have been better to say that Max Beran had a better tack; attack Dr. Spencer’s statistics and/or their interpretation. Simply detailing more facts, as Ferdinand is doing very well, doesn’t undercut the argument.
Gary Gulrud,
The interpretation of Dr. Spences (and of Max Beran) of the dCO2/dt is that temperature may have enough influence to explain a large part of the total increase. And therefore that it is impossible to know cause and effect.
But what they both do is looking at the temporarely effect of one variable, and even then one-sided. They only look at the warming part, not at the cooling part (like the 1992 Pinatubo event).
What we see in the trends is that the effect of warming and cooling temperatures have an effect on the CO2 increase speed, but that is even per year minor compared to the emissions, the other variable (in average twice the effect of temperature) and is completely dwarfed over several years.
Cyclic events like the day/night, summer/winter, El Niño/La Niña only have a temporarely effect and don’t add or substract anything after a full cycle, if the cycle is perfect. Only the difference between the start and end of the full cycle is of interest, and that is near fully controlled by the emissions, only for a very small part (less than 2 ppmv/60 ppmv) by temperature over the past 50 years…