Spencer Part2: More CO2 Peculiarities – The C13/C12 Isotope Ratio

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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Could you post a link or a citation to the data you used in your analysis?

Roy Spencer

The monthly C13/C12 ratio data from Mauna Loa (1990-2005) are available here:
The monthly Mauna Loa CO2 data (1958-2007) are contained in the 5th file listed here:

[…] CO2 Peculiarities: The C13/C12 Isotope Ratio Spencer Part2: More CO2 Peculiarities – The C13/C12 Isotope Ratio « Watts Up With That? […]

Fossil coal is buried wood. So why would you expect a difference in the C12/C13 relationship between fossil and living wood in the first place?
The annual vegetation amplitude is approx 8GtC, but it’s a cycle, what goes up comes down, whereas the fossil signal is cumulative one way.

Gary Gulrud

This would make good sense if the increase in C-13 is owed to increased temp.; increasing CO2 increasing biomass; biomass increasing C-13. Plants would respire C-13 preferentially, wouldn’t they?

Craig Loehle

Roy: can you say what would be the C13 ratio of outgassing ocean CO2 resulting from ocean warming?


I was saying that the exchanges other than industry were negative (more atmospheric CO2 absorbed than exuded).
Therefore, even if the absorption “eased off” if under “less pressure” (which in turn means you’d get diminishing benefits from CO2 cuts. What reinforces in one direction must, perforece, “un-reinforce” if headed in the other direction), any CO2 accumulation must come from man.
But Spencer seems to be challenging the basic premise. He’s saying that the evidence implies that the exchange between atmospher and ocean is NOT negative, but positive.
OTOH, Ferdinand (IIRC) or someone(s) else was saying that ony an average of 10 ppmv comes out of the ocean for every degree C, and that this matches the 100 ppm ice core measurements for the 10C swing from here to the Geological Ice Ages caused by eccentricity, wobble, and/or tilt.
But Ferdinand then indicates that CO2 emissions are estimated by ice cores to be what sees to be a SMALLER percentage drop than the historical records than the precipitous drop in industrial production and fuel consumption would seem to indicate during the Great Depression.
So I am calling the accuracy of ice-core measurement as CO2 proxy into question, not from a scientific viewpoint, but from the historical angle.
I therefore ask, do MODERN ice core measures INDEPENDENTLY match modern air-measured CO2 records? And if they do, is it possible that some of that CO2 somehow bleeds out of the archaic ice?
I want this all to add up.


“Fossil coal is buried wood. So why would you expect a difference in the C12/C13 relationship between fossil and living wood in the first place?”
Well, it must be different for C14 or carbon dating wouldn’t work. So why not for C12/13?
Come to think of it, all fossil fuel is dang old. Should maybe they should also be looking at C14 levels to determine man’s ‘contribution”?

Roy Spencer

I don’t understand the relevance of the wood issue. The natural CO2 changes appear to be related to ocean temperatures (we are just starting to look at what regions are most responsible).
The point is that the C13/C12 ratio is the SAME for the long terms TRENDS (supposedly manmade) and the NATURAL interannual variability in SSTs. So, the C13/C12 ratio does not appear to be a discriminator of an Anthropogenic source.
Also, very old ice core measurements come from highly compressed layers. How much diffusion of CO2 has there been across these thin layers of ice over thousands of years? Anything like what we have measured at Mauna Loa over the last 50 years would be smoothed out, giving the appearance of stable CO2 concentrations over centuries or millenia.

Evan Jones,
To answer your last remark first, fossil fuels still have the same d13C composition as when they were formed, many millions of years ago. 12C and 13C are stable isotopes. 14C is a radioactive carbon isotope (made by the collision of cosmic rays with nitrogen in the high stratosphere), and has a half-life time of 5730 years, see: http://en.wikipedia.org/wiki/Radiocarbon_dating.
Radiocarbon dating works for objects up to about 60,000 years. But fossil fuel is completely depleted of 14C (much too old), while current wood shows 14C/12C ratios more or less equal to the current atmospheric level.
That fossil fuel is completely depleted of 14C was observed and radiocarbon dating need a correction after about 1870, due to fossil fuel burning, up to the 1950’s, when the atomic bomb testing made radiocarbon dating impossible.

Gary Gulrud

C-14 dating ‘works’ because of radioactive decay. The half-life of 5362 (I didn’t look it up) means after that period half the C-14 has decayed. A simple differential equation is used to estimate the elapsed time. The error has been reported at <5% but some stunningly bad dates have been put forward from time to time which can happen simply from water leaching away carbon or because the original C-14 proportion is poorly estimated.
For the C-13 model age is not a first order concern, radioactivity is not involved in any way.

Gary Gulrud

Sorry, I brought up C-14 on the other thread before Dr. Spencer’s reply on the C-13/C-12 ratio because the originator, Suess, had estimated the appropriate slope using his C-14/C-12 study. I thought it important to mention that we now know the rate of C-14 creation was diminishing over his study period.

Dear Dr. Spencer,
A few remarks on the d13C changes…
To begin with, there is no practical difference in d13C of fossil fuel and vegetation decay, both are in average around -25 per mil d13C. As the seasonal changes of CO2 levels in the NH are governed by vegetation uptake and decay, it is no wonder that you can find (near) exact the same change as for the general trend.
The interesting point of d13C ratio’s is that there are only two known sources of low d13C, that are fossil fuels and decaying vegetation. All other known sources (volcanic degassing, deep oceans, ocean surface, carbonate rocks,…) have slighlty negative to slightly positive d13C values.
Thus (deep) ocean (0-4 per mil d13C) degassing can not be resposible for the decreasing trend in d13C values.
But vegetation decay can be responsible. That depends of which is prevailing: more vegetation decay than growth or the opposite.
Lucky, we have another, independent, measurement to know which one is prevailing: oxygen use or production. Since about 1990 we have oxygen measurements (at the edge of analytical possibilities), which are accurate enough to see the small difference between oxygen use from fossil fuel burning and the oxygen use/production of vegetation decay/growth.
This revealed that (at least) since 1990, somewhat less oxygen was used than calculated from fossil fuel burning. Thus vegetation produces more oxygen than it uses. And as vegetation growth prefers 12C over 13C, more 13C is left in the atmosphere. Vegetation thus is not the cause of the d13C decline…
As fossil fuel burning is the only known source of 13C depletion in the atmosphere left, it probably is entirely responsible for the whole d13C decrease…
For a more in-depth analyses of the d13C/O2 analyses and the resulting partitioning of CO2 sinks between oceans and vegetation, see Battle ea.:

Roy Spencer

Thanks, Ferdinand, for the very informative post.
It now looks like it is the warm ocean areas of the west Pacific and Indian Ocean that are highly correlated with the interannual variations in CO2 at Mauna Loa. So, this sounds more like some sort of temperature-related outgassing, doesn’t it? (The upwelling zones show little or no correlation. There is also a large area of high correlations over the entire eastern North Atlantic.)
This paper on “The Global CO2 Survey” shows that the ocean-atmosphere exchange is a strong function of wind speed…so that could be involved, too:

Roy Spencer

You said: “To begin with, there is no practical difference in d13C of fossil fuel and vegetation decay, both are in average around -25 per mil d13C. As the seasonal changes of CO2 levels in the NH are governed by vegetation uptake and decay, it is no wonder that you can find (near) exact the same change as for the general trend.”
But it’s not the seasonal signal I’m measuring. It’s interannual variability (running 12-month averaging removes the seasonal signal). And since that signal correlates much better with SST than it does N.H. land temperatures, I’m assuming that the CO2 in question is coming from, and going into, the ocean
You said: “As fossil fuel burning is the only known source of 13C depletion in the atmosphere left, it probably is entirely responsible for the whole d13C decrease”
I’me beginning to wonder whether you read my post, Ferdinand. I already showed that the interannual variability has exactly the same ratio of C13/C12 as does the trend. So, how is it that mankind is responsible for decreasing dC13 in the long term, but natural variability (which has exactly the same C13/C12 relationship) can be ruled out for the long-term trend?

Dan Evens

What is the physical process in which C12 moves into plants faster than C13?

Roy you are referring to the CO2 thermometer that Jarl Ahlbeck discovered, and for which he demonstrated that the UAH sat temperature is a better metric than the surface temperature (!).
The South Pole has an even more distinctive ENSO signature in the CO2 growth:
(NOAA acknowledged herewith)
monthly dCO2/dy graph here:
But that’s not the point is it? What we see is not a temperature dependent source, but a temperature dependent sink flux! Or in electronic equivalent: we see a temperature dependent power source, and a temperature dependent resistance:
I= V(T)/R(T) +constants
But the V(T) part is only 10 ppm/K, whereas the R(T) part is 4 ppm/y/K. So what you see in Mauna Loa (and South Pole) is that the flux resistance is temperature modulated, and not the gradient itself, that is only visible in ice cores.
Also the sink flux is in first order proportional to the excess gradient as is observed, and is dictated by Fick’s law (diffusion) or Ohm’s law (electricity). In warm years CO2 accumulates in the atmosphere, only increasing the gradient, which will flow out even more rapid in colder cycle years. So I also don’t see a reason why CO2 should remain in the atmosphere “forever”, as some alarmists want us to believe.
As the sink flux is also dCO2/dt=KCO2 we immediately see the solution to the differential equation that governs the CO2 sink flux: an e-folding decay function for a spike input, a Peter Dietze demonstrated 55 years.

Dear Dr. Spencer,
I think that we need to take into account the different mechanisms which govern d13C and total CO2 changes vs. temperature. And between seasonal variations and interannual variations in temperature.
– If the temperature increases, this has opposite effects for vegetation and oceans on CO2 flows: more CO2 release in the tropics, less absorption near the poles for oceans. But more CO2 uptake by plants (especially in the mid-latitudes). This leads to more CO2 uptake in summer and more decay over the whole year.
The CO2 uptake by plants wins in the case of seasonal changes (lower CO2 levels) for the NH (more vegetation), but there is little variation in the SH.
The CO2 release/less uptake by oceans wins in the case of interannual temperature changes, that is what we see for the ppmv/°C changes.
– If the temperature increases, this has similar effects for oceans and vegetation: more degassing of 13C rich CO2 (0-4 d13C) vs. the atmosphere (-8 per mil d13C), more 12C uptake by vegetation, leaving relative more 13C in the atmosphere. Both increase the d13C level.
– But we see that in the atmosphere (ice cores – firn – atmosphere), as well as in the upper oceans (coralline sponges), d13C levels decline, starting around 1850. See:
Thus the long term trend has had little influence from interannual natural variations, neither from increasing temperatures…

Dear Dr. Spencer,
My previous post was sent before I had read your reaction…
Here some more clarification:
In general, we can say that over a relative short time span we have three influences with increasing SST:
– the influence of the emissions (in general twice the CO2 variation, but near equal at El Niño episodes) on CO2 levels: increasing, on d13C levels: decreasing, not influenced by temperature.
– the influence of vegetation on CO2 levels: decreasing, 13C levels: increasing.
– the influence of the oceans on CO2 levels: increasing, 13 C levels: increasing.
The total influence on CO2 is (based on a few guesses):
+7 GtC with -24 per mil d13C from the emissions
-2 GtC wich acts as +24 per mil d13C from vegetation uptake
+2.5 GtC with 0 per mil d13C from warmer oceans.
Total increase (observed in the atmosphere): +7.5 GtC
Effect on atmospheric d13C (observed in the atmosphere): – 0.05 per mil d13C
The latter can be calculated, including the 90 GtC seasonal ocean exchanges (which dilute the emissions fingerprint with about 20%), but it may be clear from this figures that the 7 GtC from the emissions with very low d13C minus 2 GtC with very high d13C by far outweigh the 2.5 GtC with near zero d13C from the oceans. This only temporarely reduces the decrease speed, not the decrease itself.
One need about 4 GtC from the (deep) oceans to compensate 1 GtC from the emissions with a neutral effect on atmospheric d13C levels…
Thus even during natural variations, the d13C decrease from the emissions by far dominates the change in ratio’s, that is why you don’t see a difference between short term and long term variations in d13C.

Forgot to add: the figures used were for the 1998 El Niño year…

Roy Spencer

Thanks for the detailed explanation. It will take me awhile to digest all of the various numbers and compensating influences in the carbon budget you have listed.
I was under the impression that we didn’t understand the details of the carbon cycle…but obviously, I was mistaken. 😉

Dr. Spencer makes some convincing arguements.
I would hasten to add, however, that much of the “ice core average global
temperature” is based on the Oxygen 16 to Oxygen 18 ratios.
The problem with this “proxy”, which I have yet to illuminate a good rational for, is that the geo-physics types have used this number to trace water flows from various areas as it has been established that WARM WEATHER thunderstorms in costal areas push the O18 up (significantly, as in a 30% higher isotope concentration).
As such, the O18 to O16 ratio, as far as I’m concerned, gives perhaps an “atmopheric energy” indication (i.e., a number reflecting the number of warm weather T.S.’s versus cold weather, continental ones), but does NOT give a reasonable proxy for “global temperature”.
I read a less rigorous computation, years ago..making the fundamental mistake Dr. Spencer has pointed out…and one of my first thoughts was,
“Is there some other ‘mechanism’ which could shift isotope ratios around?”.
Thus, I’m totally CAUTIOUS about drawing “yea” or “ney” conclusions on the isotope ratios.

Tim Rutkevich

Hans Erren wrote(05:34:29) :
Fossil coal is buried wood. So why would you expect a difference in the C12/C13 relationship between fossil and living wood in the first place?
The annual vegetation amplitude is approx 8GtC, but it’s a cycle, what goes up comes down, whereas the fossil signal is cumulative one way.
Plants have preference for the “lighter” C12. If you would look at the total Carbon cycle, you would see that geological CO2 emissions have higher concentrations of C13. If you would attribute all increases in CO2 to the anthropogenic i.e. fossil origin C. The balance should change to C12 side. What it means: oceans and earth plants are able to deal with all anthropogenic CO2. What we have is geological outgassing that changing concentration of CO2 in the atmosphere.


Very interesting.
Hard to follow, but very interesting. (If I didn’t have a handle on the 5th-grade version of the exchange rates I wouldn’t be anywhere close.)
To let man off the hook:
It’s the ocean because the C12 ratio is not increasing. The stuff man is putting out is absorbed. Man’s contibution to ocean sink is lost in the crowd (6.3-to-38,000 BMTC). PDO/AMO or whatever causes the increase in upper ocean temperatures and C13 exudes. (Which I think RS is saying.)
To blame it on man:
Is it possible that the fossil-fuelC12 is being absorbed by the ocean but this is creating upper ocean saturation and therefore forcing increased C13 outgassing? The C12 incease being lost in the sink, masking the anthropogenic fingerprint? (Which I think FE is saying.)
Is this a correct 5th-grade understanding of the argument?


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!


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:
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…

Paul Dennis

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!

E Mohr

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?

Steve Keohane

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?

Roy Spencer

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:
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…

Stan Needham

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.

E. Mohr

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):

The d14C of the carbon flux into the terrestrial biosphere or ocean surface is exactly the same as the d14C of atmospheric CO2 at the time of flux

I found a very interesting slide show about 13C and 14C exchanges here:
http://tinyurl.com/2jyvqs by Jim Randersom.
This includes slides about atmospheric CO2 mixing and the d14C decrease in the atmosphere pre-nuclear bomb testing.
I haven’t thought much about the d14C changes since the industrial revolution, but it gives interesting perspectives. While it is impossible to make a distinction between vegetation decay and fossil fuel d13C changes, d14C gives a clue, as fossil fuel is completely depleted of 14C.
This is already used to distinguish between natural/human contribution of diurnal CO2 changes on land, soot deposits (wood vs. coal) and the biogenic/ocean flows determination (based on pre- and post nuclear bomb tests d14C fate)…

E. Mohr,

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.

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)
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?

Gary Gulrud

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.


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.

Gary Gulrud

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…