I’ve often stated that we are sure the increase in atmospheric CO2 is due to human activity because of the relative abundance of different isotopes of carbon in the CO2. There are two stable isotopes of carbon: 12C, and 13C. They differ mainly in their weight; 12C weighs 12 atomic mass units (amu) while 13C weighs 13 amu. Most carbon is the “normal” isotope 12C, but about 1% of earth’s carbon is the heavier 13C.
Plants, when they “breathe in” CO2, show a strong preference for that which contains the more common isotope: 12CO2. It’s long-dead plant matter that supplies the carbon which is the active ingredient in fossil fuels (oil, gas, coal). So, the carbon in fossil fuels is depleted in the heavier isotope 13C.
This means that IF the rise in atmospheric CO2 is due to the burning of fossil fuels, then almost all of the “new” CO2 should be made with the lighter isotope: 12CO2. This means that the amount of 12CO2 in the atmosphere will be increasing, but the amount of 13CO2 will not. And that means that the fraction of atmospheric carbon dioxide which contains the heavier isotope, 13CO2, should be decreasing.
In fact, not only is atmospheric CO2 on the rise overall, it also shows an annual cycle of ups-and-downs due to the respiration of land plants. IF the rise is due to burning fossil fuels, then that rise includes almost no 13CO2. Also, plant respiration involves almost no 13CO2. So, IF the rise is due to burning fossil fuels, then as CO2 rises the fraction which is 13CO2 should fall, and as it wiggles up and down due to plant respiration, the fraction which is 13CO2 should wiggle down and up — in an opposite cycle.
So what really happens? I recently acquired data on atmospheric fraction of 13CO2 from 1990 to 2005. This is measured as 
Here’s the atmospheric CO2 concentration (black line), together with the atmospheric
Just as expected, while CO2 has been increasing,
This is a “smoking gun” proving that the increase in atmospheric CO2 is not from natural sources like volcanic activity. It’s due to the burning of fossil fuels — by humankind.
Incidentally, I got the data from a new data website, giving lots of information on atmospheric gases. It’s maintained by Japan’s meteorological agency, in association with the World Meteorological Organization: the World Data Centre for Greenhouse Gases (WDCGG). It has information of a lot of different gases, including:
- carbon dioxide (CO2)
- methane (CH4)
- nitrous oxide (N2O)
- sulfur hexaflouride (SF6)
- chloroflourocarbons (CFCs)
- hydrochloroflourocarbons (HCFCs)
- hydroflourocarbons (HFCs)
- tetrachloromethane (CCl4)
- trichloroethane (CH3CCl3
- trichloromethane (CHCl3)
- dichloromethane (CH2Cl2)
- perchloroethylene (C2Cl4)
- surface ozone (O3)
- carbon monoxide (CO)
- nitrogen monoxide (NO)
- nitrogen doxide (NO2)
- sulfur dioxide (SO2)
- volatile organic compounds (VOCs)
- organic peroxide (ROOH)
- hydrogen peroxide (H2O2)
- hydrogen (H2)
- 13C-isotopic carbon dioxide (13CO2)
- radon (222Rn)
- 18O-isotopic carbon dioxide (C18O2)
- 13C-isotopic methane (13CH4)
- peroxy acetyl nitrate (PAN)
- chloromethane (CClH3)
- bromomethane (CHBr)
That’s a lot of gases! Not all of them are greenhouse gases, but a lot of them are.
It’s a reminder that CO2 isn’t the only greenhouse gas which is increasing due to human activity. The latest IPCC summary for policymakers has graphs showing the change in three greenhouse gases over time:
While CO2 exists in much stronger concentration than the other greenhouse gases, many of the others are more potent than CO2 on a per-molecule basis. That’s why, even though CO2 is measured in parts per million while methane is measured in parts per billion, methane is strongly in 2nd place in terms of its climate effect:
CO2 gets the most press coverage, because it is after all the most plentiful man-made greenhouse gas, and makes the largest contribution to global warming. But methane has also gotten a lot of press, because not only is it a strong 2nd place contributor (it’s a lot less plentiful than CO2, but also a lot stronger on a per-molecule basis), one of the sources is rumination (farts) from animals (especially the ones we like to eat, cows). Some denialists have attempted to ridicule global warming by pointing to the statement that significant greenhouse-warming effect is due to “cow farts.” I guess they think it sounds ridiculous. I think they sound ridiculous.
33 responses so far ↓
Adam // March 9, 2007 at 3:31 pm
I seem to recall a discussion on cow emissions that stated that they were really burps. Not sure where, and whether it’s any use, but there you go.
Good post (as usual), BTW.
content source » Blog Archive » It’sa Gas // March 9, 2007 at 5:28 pm
[...] Original post by tamino [...]
G Farley // March 9, 2007 at 7:26 pm
I think you’re information about the relative abundance of C12 and C13 was very interesting and seems to me to be excellent evidence that the changes in CO2 concentration are associated with human activity. However I don’t see that this is any indication that CO2 is the main cause of climatic warming.
I was interested in the recent Dispatches tv program’s statement that when the historical correlation of CO2 with climatic warming over hundreds of thousands of years was examined in detail, the warmings preceded the CO2 increases and that CO2 was therefore an effect rather than a cause of warming.
Is there something misleading about that point of theirs ?
(I understand that this correlation had been used as an argument for warming being an effect of CO2, by eg Al Gore and others urging a reduction in CO2 emissions)
tamino // March 9, 2007 at 9:26 pm
To G. Farley:
Indeed it’s not, but that’s not the topic of this particular post.
Don’t know what TV program you’re referring to (is it the recent one on British TV? — I’m in the states). It’s true that during the ice ages (during a deglaciation) temperature increase begins before CO2 increase begins, typically by about 800 yr. But by the time CO2 increase sets in, global temperature has only increased a little (less than 1 deg.C). It still has a long way to go to make for a full deglaciation (about 5 deg.C global average temperature change).
The warming influence which *starts* global warming during a deglaciation is ice-albedo feedback. Changes in earth’s orbital parameters (Milankovitch cycles) re-distribute incoming solar energy so that more of it hits high latitudes. This causes melting of the ice sheets, which exposes open land and sea where there once was ice. Ice is highly reflective (high “albedo”) and sends most of the incoming solar energy bouncing right back to space, but open land and sea are not nearly so highly reflective so more incoming solar energy is absorbed, and becomes part of the climate system. So, even though orbital changes don’t alter the total solar energy showing up at our doorstep (at least not by very much), the melting of polar ice alters the amount of solar energy which gets past the “bouncer” into the nightclub. More energy into the climate system, starts the process of global warming.
But the extra energy from ice-albedo feedback isn’t enough to explain the total 5 deg.C global warming from glacial to interglacial conditions. However, there’s another feedback mechanism at work: CO2. The warming which is started by ice-albedo change, warms the oceans, and warming water reduces the solubility of CO2. Reduced solubility means the oceans give up some of their vast store of CO2 to the atmosphere. This causes greenhouse-gas warming. This further warming leads to more ice-melt, and yet more CO2 from the oceans, both of which lead to yet more warming.
So, both claims are correct: warming causes CO2 increase AND CO2 increase causes warming. It’s a classic “feedback mechanism.” The best estimates I’ve seen are that during a deglaciation, ice-albedo change is responsible for about 3 deg.C warming and greenhouse gases about 2 deg.C, making a net 5 deg.C change.
As you can tell, during a deglaciation the situation is not so simple as “CO2 increase causes warming” or “warming causes CO2 increase.” Both factors are both cause and effect.
Whether it’s misleading or not, depends on the context in which it’s stated. If it’s suggested that this is the only factor at work, and that warming-causes-CO2 means CO2-does-not-cause-warming, then yes, it’s very misleading — and deliberately so. If it’s suggested that the situation is a lot more complicated than just a single-cause scenario, then it’s just a statement about the science of things. The fact that you say they claim, “… that CO2 was therefore an effect rather than a cause of warming,” leads me to suspect that they’re being deliberately misleading.
When Al Gore (in An Inconvenient Truth) points to the correlation between CO2 and temperature, he definitely implies a causal relationship (CO2 causes warming) but doesn’t explicitly state that that’s the only factor at work, nor does he in any way state or imply that there’s no “effect” relationship to go with the “cause.” Some climate scientists have criticized him for omitting to mention the two-way street, but others regard his presentation as fully honest.
Gareth // March 9, 2007 at 11:12 pm
Thanks for that very clear exposition on CO2’s role in deglaciation. Worth promoting to a post of its own, perhaps?
And I can confirm that ruminants burp their CH4. What comes out the other end is a source of N2O.
[Response: I've done several posts on ice ages -- one of my favorite topics -- but maybe you're right, it would be good to do a post on the basic processes, attempting to give a better picture of the "whole story." There's a lot to tell, but I believe it can be done in a way which is understandable even to the newcomer.
And thanks for the info about ruminant CH4 and N2O. You learn something new every day.]
G Farley // March 10, 2007 at 12:15 pm
In analysing the historical warming/CO2 graph, put forward by Al Gore in his presentations (havnt read the book), as evidence for the warming effect of atmospheric CO2, I’m tempted to differentiate facts from opinions. AFAICS the interesting facts to be gleaned from this particular dataset are a) that at least the initial increase in CO2 is a consequence not a result of warming and b) that the CO2 fluctuations are a subordinate phenomenon ie even after a long period of rising levels, something is able to reverse the trend, despite the positive feedback effect of those higher CO2 levels.
It may very well be that CO2 produces a significant warming effect, but there is no way to determine that from this data. It is an opinion that needs additional information to validate.
Given that the tv programme was debunking Al Gore’s suggestion that this graph demonstrated historical CO2 levels caused warming, their comments seems fine. I think I’d have to line up and join the camp of people who would classify Al Gore’s presentation as suspect.
If we decide to discount expert opinion on the issue of whether man-made CO2 significantly influences global temperatures, we need access to the agreed fundamental data, together with a convincing analysis of it that we can all agree with. I wonder where this can be found ?
G Farley // March 10, 2007 at 12:15 pm
oops ‘consequence not a cause’
guthrie // March 10, 2007 at 9:04 pm
The IPPC fourth report, I believe, which will be out in a wee while.
If you want something else about it all to get your teeth into, try this:
http://www.aip.org/history/climate/
Its an entire online book about the history of our knowledge of climate change, including interesting things about how back in the 19th century John Tyndal found that CO2 could trap heat, and Arrhenius did some calculations about the effects of changing CO2 levels in the atmosphere.
Joe Cool // March 10, 2007 at 11:31 pm
I didn’t know about this isotope separation, had always assumed is was calculated from industry figures.
However, your article is flawed as further research indicates that 13CO2 is the ocean-land interaction contribution to co2 concentration.
Fossil fuel contribution is 14CO2 (and I don’t see that data on the Japanese site…nice find btw)
[Response: Fossil fuels are almost totally depleted in 14C, because that's not a stable isotope. It has a half-life of about 6000 yr, and fossil fuels have been buried for millions of years.
Do you have a reference for the further research you refer to?]
CraigM // March 11, 2007 at 12:59 am
“This is a “smoking gun” proving that the increase in atmospheric CO2 is not from natural sources like volcanic activity.”
To prove man is the cause of the recent rise in c02 levels it’s enough to show me a few graphs of how anomalous the recent rise in c02 is (as you did in ‘fast c02′). Atmospheric c02 has risen by approx 30% up to 380ppm from 280ppm. It was stable at 280ppm for thousands of years. Its varied between 180-280ppm over the last 100,000 years. The recent release coincides with the industrial revolution. Thats usually enough for me…but obviously not others.
I skim read a post on this carbon 12 and carbon 13 stuff over a realclimate, didnt really grasp it too well. Let me get it straight. The % of C12 in the atmosphere relative to C13 has increased. c13 comes from volcanoes. C12 from plants and fossil fuels (dead plants). Therefore we can rule out volcanoes?
What about other sources of c12 other than fossil fuels. As far as i can see you have only 2: the ocean, the biophere (living things like trees etc). Thats my limited knowledge of the carbon cycle.
I think you might know that one of the regular claims from denialists is that natural emissions dwarf human emissions. Which is true. For example the ocean i believe annually emitts 90 gig tonnes of c02, and this dwarfs our emissions annually. But they neglect to mention that the ocean absorbs 90 GT annually too. So the net contribution is zero. In fact the oceans are getting more acidic (like coke) so they are actually absorbing more than they emitt. So rule out the oceans (i recently met someone who tried to claim the oceans were the cause of recent c02 rise)
For me the evidence that man is the cause of the recent warming goes something like this:
-the rise in c02 is extremely anomalous
-the rise coincides with the industrial revolution
- we have pumped enough stuff into the atmosphere to raise atmospheric c02 by 500ppm
-c12 is increasing relative to c13…rule out volcanoes?
-the oceans are more acidic. rule out oceans.
-deforrestation, well thats been happening, but its caused by us.
Its all something like that?
[Response: Sounds to me like you've got a pretty good handle on things. I would add that volcanos don't discriminate between 12C and 13C; as far as I know only biological processes discriminate strongly, so if 12C goes up while 13C does not, it implicates organic matter.]
CraigM // March 11, 2007 at 1:05 am
“For me the evidence that man is the cause of the recent warming goes something like this:”
This should actually say:
“For me the evidence that man is the cause of the >recent rise in c02 levels
Eli Rabett // March 11, 2007 at 1:51 am
The amount of CO2 from volcanos is monitored. See the USGS volcano web pages. There just is not enough of it.
Eli Rabett // March 11, 2007 at 1:54 am
The dilution of C14 in the atmosphere is called the Suess effect. Google it. Basically fossil fuel has no C14 because it has all decayed away, so the decline in the ratio of C14/C12 is an indicator of how much fossil fuel has been burned.
G Farley // March 11, 2007 at 9:15 am
It sounds like there’s not much doubt that humans have raised CO2 levels - but the key question is ‘are those raised levels causing the recent warming ?’
tamino // March 11, 2007 at 2:57 pm
CO2 does absorb infrared radiation; it’s been measured in the laboratory countless times. In fact the absorption of infrared can be used to measure CO2 concentration in gas samples. Therefore unless physics is fundamentally wrong, CO2 will act as a greenhouse gas: it will warm the planet.
Since the beginning of the industrial age, CO2 has been increasing in the atmosphere due to human activity. Since about 1975, CO2 concentration has gotten so high that its greenhouse effect dominates other climate factors (which are also quite thoroughly studied).
And lo and behold, since about 1975 the planet has been warming significantly — at nearly 0.2 deg.C/decade.
We can even use the laws of physics to build computer models of global climate change. When we plug in all the known factors except man-made greenhouse gases, the calculations of the models don’t match what we’ve observed over the last century and a half. But when we include the effect of man-made greenhouse gases, the match is near-perfect.
It’s like your wife decides to put an extra blanket on the bed. You sleep warmer. But she keeps putting another blanket on the bed every week. By the time you have 20 extra blankets, you’re uncomfortably warm.
But your wife insists that it’s not the extra blankets that are making the two of you so warm night; it’s galactic cosmic rays. You reply that we know there are extra blankets on the bed, and there’s no doubt that she’s the cause. But she insists that the key question is, “are those extra blankets causing the recent warming?”
If you want to deny anthropogenic global warming, not only do you have to show what’s causing the recent warming (and absolutely no alternative explanation passes muster), you also have to show how it’s possible that greenhouse gases do not.
G Farley // March 11, 2007 at 8:26 pm
To tamino:-
The question is whether the increment in CO2 levels contributed by humans is significant – ie is it the actual cause of the warming.
Eg in terms of your analogy, are we putting a blanket on the bed or a wisp of fluff ?
Of course potentially it might be, but is it ? can we totally ignore: ‘solar activity’ or even ‘natural fluctuations within a chaotic system’.
Having written the above sentence I was spurred to do enormous amounts of research ie googled ‘sunspot records’
it would seem that global temperature was higher a few thousand years ago when solar activity (=>sunspots) was higher than it is today.
http://en.wikipedia.org/wiki/Image:Holocene_Temperature_Variations.png
[Response: If you look carefully at the graph and read the accompanying description, you'll notice that the thick black line indicates the average of the given estimates, while the thin colored lines are temperatures at isolated locations. Therefore the thick black line constitutes the only estimate of past *global* temperature in that graph. You'll also notice that the maximum (during the "holocene climate optimum") isn't nearly so warm as it today (which is indicated by the "2004" arrow on the left-hand-side of the plot; like most paleoclimate plots, in that graph time runs from right to left rather than left to right).]
Recently (60 years ago) the sun started to become more active again.
http://dsc.discovery.com/news/briefs/20041025/sunspot.html
[Response: We don't need tree rings to analyze sunspot activity recently; they've been observed directly since the 1600s. Indeed there was an increase in activity (about 100 years ago), and that is partly (but not entirely) responsible for the global warming observed in the early part of the 20th century.
But the increase in solar output can be estimated rather well, and isn't nearly enough to account for all the warming in the early 20th century, let alone the modern warming. The total increase over the last century in average total solar irradiance (TSI) is not more than 1.6 watts per square meter (W/m^2); but since the sunlight intercepted by earth is proportional to its cross-sectional area, and gets spread out over its entire surface area -- which is exactly 4 times the cross-sectional area -- and about 30% of incoming sunlight bounces right back to space (never entering the climate system at all), the increase in *climate forcing* due to increased solar activity is less than 0.3 W/m^2. By contrast, we've already seen much more increased climate forcing due to CO2: about 1.8 W/m^2.
And, solar activity stopped increasing around 1950. The modern global warming era (and its concomitant rapid warming) starts around 1975. Check out this post for more details.
So, when examined critically, the "increased solar activity" hypothesis just doesn't match observed facts. That's why solar advocates have taken to some pretty exotic theories (like galactic cosmic rays) in an attempt to revive the sun as the prime mover of global temperature.]
At first sight this seems a plausible alternative explanation ?
I suspect that a quantitative rather than aqualitative explanation is required in this case in order to choose amongst available explanations.
Adam // March 14, 2007 at 9:27 am
For anyone still unsure about the T/CO2 lead/lag “issue” in the past, there’s some useful discussion of it at Stoat:
http://scienceblogs.com/stoat/
Fergus Brown // March 15, 2007 at 3:31 pm
Tamino: somebody asked me this question & I have no idea of the answer: perhaps you can help?
‘The problem I have with this is that the forced increase in temperatures will lead to further increases in CO2 - a perfect, and direct, feedback mechanism - but shouldn’t this mean that the graphs from the Vostok Ice Core should show exponential curves at each major upturn in temp and CO2? I’m sure that audio feedback follows this exponential curve, and I was under the impression that any direct feedback loop would do the same. So why do the Vostok graphs show linear increases in temperature and CO2?’
In anticipation, Regards,
It's not the Volcanoes « Fermi Paradox // April 13, 2007 at 6:22 am
[...] But that is not all. tamino at Open Mind explains that the isotope ratios also show that the carbon dioxide is coming from fossil fuels. [...]
george // April 21, 2007 at 4:46 am
Fergus brown said that someone presented him with the following “issue” (a non-issue, really)
“The problem I have with this is that the forced increase in temperatures will lead to further increases in CO2 - a perfect, and direct, feedback mechanism - but shouldn’t this mean that the graphs from the Vostok Ice Core should show exponential curves at each major upturn in temp and CO2? ”
No, and it’s pretty easy to see why.
The basic reason positive feedback in this case does not lead to exponentially increasing temperature is that each new CO2 “increment” of a given size that is added to the atmosphere (from the ocean, in this case) causes a smaller change in temperature than the last increment of the same size did.
First, let me point out that the CO2 “solubility vs temperature” curve for water is essentially linear over the range of temperatures that applies to the (ice core) cases in question, so for every one degree C rise in the temperature of ocean water, there is essentially the same amount of CO2 released (same amount of dissolved CO2 that comes out of solution).
But the amount of temperature change for a given increment of CO2 released from the ocean into the atmosphere decreases as the atmospheric CO2 concentration builds up, so it is a process of diminishing returns – and not just with regard to temperature increase.
Since each subsequent increment of CO2 released by the ocean leads to a smaller temperature increase, it also leads to the subsequent release of a smaller increment of CO2 (since the amount of CO2 released is proportional to the temperature change of the water), which in turn leads to an even smaller temperature increase, which leads to release of a smaller increment of CO2 and so on…
Greenhouse gases other than CO2 (methane, for example) are also undoubtedly involved in the positive feedback cycle, but they are still bound to obey the same basic physical law with regard to the amount of temperature increase induced for release of a given amount of gas as a function of the atmospheric concentration of the particular gas in question.
That’s simply not the recipe for “exponentially escalating temperatures” as some have claimed.
george // April 21, 2007 at 4:07 pm
Tamino said: “Plants, when they “breathe in” CO2, show a strong preference for that which contains the more common isotope: 12CO2.”
This is a very interesting statement, to say the least. Downright mysterious, actually.
Assuming that plants take in both C12 and C13, how do they differentiate between the two isotopes — or at least, how do they differentiate between the carbon dioxide molecules that the carbon isotopes reside in?
It is oft stated that “isotopes have identical chemical properties”, but this case obviously makes that claim suspect (assuming that plants are not differentiating between the two isotopes based on weight, which would be exceedingly difficult, to say the least, though it can’t be ruled out)
Through a brief search, I was only able to find the following “explanation” (just a statement, really)
“plants have an enzyme that discriminates against rare carbon-13 isotopes”
But enzymes discriminate based on shapes and sizes of molecules and on bonding between the enzyme and the molecule in question. These, in turn, are based on the details of the electronic orbitals in the target molecule (and in the enzyme).
This implies that the bonding (or more precisely, the electronic orbitals leading to the bonding) in a carbon dioxide molecule with a C13 atom is different than that in the carbon dioxide with C12.
Since carbon dioxide is a linear molecule, the molecule shape, at least, would be the same for the carbon dioxide with C12 and C13.
Different isotopes do have slightly different electronic energy levels, which affects bonding, but it must be a rather subtle effect in this case.
Looking around a little more, I discovered this in “Chemical effects of isotopic substitution” in Britannica online:
“While isotopic substitutions usually change chemical equilibrium constants by small amounts, they can increase the rates of chemical reactions by a factor of 10 or more in the most extreme cases.”
The last part of that is consistent with the statement above that “plants have an enzyme that discriminates against rare carbon-13 isotopes” because enzymes act as catalysts that speed up reactions.
But that still does not explain anything about the details of the mechanism, which I am assuming someone must have studied.
And this all begs another obvious question with regard to carbon 14, which plants do use (and which is used in radio-carbon dating)
Why is it plants like C14 but not C13 ?
Obviously there are some very subtle discriminations going on here with regard to bond energies and/or excited electronic states (or something else?) affected by the isotopic substitution.
Then again, perhaps plants just like even numbers.
Or perhaps they are are superstitious and just don’t like the number 13 (who can blame them?).
Perhaps someone else has more information on this subject than I was able to find (my internet search was admittedly very brief)
It’s all very interesting and more than a little mysterious.
[Response: I'm no expert on this, but I'm not sure that plants fail to discriminate against C14; they do use it, but they also use small amounts of C13 -- just less than atmospheric concentration.
I suspect that the main difference of C14/C13/C12 for these reactions is *physical*. Mass can have a profound impact on chemical and physical reactions, and the mass of C14/C13 is significantly different from that of C12.
But this is my speculation, I really don't know.]
george // April 21, 2007 at 6:28 pm
The C12/C13 discrimination apparently occurs by way of several mechanisms, both physical (diffusion) and chemical (ge, bond-related enzyme catalyzed reaction):
I found a paper that talks about basic mechanisms for the process
Carbon isotope discrimination as a tool to screen for improved drought tolerance
Author: Bert Cregg1 and Jianwei Zhang2
“The isotopic ratio of 13C to 12C in plant tissue is less than the isotopic ratio of 13C to 12C in the atmosphere, indicating that plants discriminate against 13C during photosynthesis. The isotopic ratio of 13C to 12C in C3 plants (d13C) varies mainly due to discrimination during diffusion and enzymatic processes. The rate of diffusion of 13CO2 across the stomatal pore is lower than that of 12CO2 by a factor of 4.4‰. Additionally, there is an isotope effect caused by the preference of ribulose bisphosphate carboxylase (Rubisco) for 12CO2 over 13CO2 (by a factor of ~27‰). In both cases, the processes discriminate against the heavier isotope, 13C (Farquhar et al. 1989). ”
Wikipedia has this to say about the
kinetic isotope effect (KIE) is a variation in the reaction rate of a chemical reaction when an atom in one of the reactants is replaced by one of its isotopes. It is also called isotope fractionation.”
“Isotopic substitution can modify the rate of reaction in a variety of ways. In many cases, the rate difference can be rationalized by noting that the mass of an atom affects the vibration frequency of the chemical bond that it forms, even if the electron configuration is nearly identical. Heavier atoms will (classically) lead to lower vibration frequencies, or, viewed quantum mechanically, will have lower zero-point energy. With a lower zero-point energy, more energy must be supplied to break the bond, resulting in a higher activation energy for bond cleavage, which in turn lowers the measured rate.
“a 12C reaction is only ~1.04 times faster than the corresponding 13C reaction (even though, in both cases, the isotope is one atomic mass unit heavier).”
I also found another paper that indicates there is also apparently “photosynthetic discrimination” and “post-photosynthetic discrimination” of the two isotopes leading to different isotope ratios in different plant tissues (roots, leaves etc).
Based on the few papers I have looked at, it all looks very complicated. It’s really no wonder the AGW denialists never even go near this kind of stuff in their denials!
buck // May 1, 2007 at 3:15 am
Thank you for an attempt at forming an unbiased opinion as the the effects of CO2 on global warming.
I would like to see that 13C : 12C data replotted as 12C on the X-Axis and 13C on the Y-Axis. Seems to me that that would further quantify this relationship.
Julian Flood // November 12, 2007 at 8:44 pm
Oh, yes, I forgot to mention: plants use 3 different methods of carbon fixation, C3, C4 and CAM. C3 discriminates against the heavier isotopes, CAM less so, C4 least.
C4 is the method used by things like maize — it reduces the amount of CO2 used and thus means the plant can close its stomata sooner — a handy trick if you are in a desert area and need to avoid wasting water. Lovelock, BTW, suggests that Gaia will have to switch to C4 if it uses lower CO2 levels to control temperatures. (If I were Gaia I’d just make more clouds, but I’m not a CO2 fan.)
There’s another reason for using C4 — shortage of certain nutrients needed for the C3 enzymes. I think it’s zinc and chromium, but I’ve read so much recently that it’s a bit of a blur.
As the oceans warm, there is less nutrient flow to the surface. Starved of Cr and Zn, some phytoplankton switch from C3 to C4 and those that can’t are to some extent outcompeted by obligate C4 types. They fix CO2 without discriminating so much between the isotopes. They rain out a slightly heavier C mix and thus the atmosphere shows a reduction, relatively, in the C13 and C14 atoms. How can we discriminate between this scenario and the approved smoking gun?
Some volcanoes send out dust rich in leachates: the ones which emit the C3 enzyme’s stuff should cause an apparent reduced fossil-fuel-use pulse of discriminated against heavy atoms into the atmosphere as the C3 phytos perk up. I wonder if it shows?
I’d really like some advice about this. There’s a study in the Gulf which shows isotope changes starting in 1750. 1750? What the hell is that about? I’ve seen recent suggestions that AGW has only really kicked in in the last 60 years. 250 years is even before my own preferred date at 1850 (the start of the petrochemical revolution) and, unless we were spilling megalitres of whale oil, I’m at a loss to explain it.
A cooking tip: if you like dolmades, pick your vine leaves first thing in the morning. Vitis vinifera is a CAM plant and stores waste CO2 overnight as malic acid, which gives the wrapping a lovely sharp taste. Enjoy….
JF
[Response: You should read this excellent writeup on the carbon cycle.
And "a study in the Gulf" isn't a very good reference.]
Hank Roberts // November 12, 2007 at 10:04 pm
Say Tamino, would you remove the email address from JF’s post dated 9/18 above? The spam-harvesters pick this stuff up forever, I notice.
[Response: I don't see an email address in his post; there is a link to his website (as many commenters have) but I suppose that's up to him. WordPress allows me access to his email address but I don't think spammers can get to it. Is there something else you see?]
dhogaza // November 12, 2007 at 11:43 pm
I’m seeing *my* email address up there.
Someone put in some broken HTML apparently that exposes my e-mail from a previous post to all?
[Response: This is a very serious breech. But I still don't see anybody's email address
I've deleted the Julian Flood post from Sep 18. Does that make the email addresses disappear?
Can one of you fellows copy-and-paste exactly what you see, or even do a screen capture, and send it to me]
Hank Roberts // November 13, 2007 at 1:23 am
This is weird — okay, I know what happened, but not why.
That post that you deleted was misplacing the email address that appears under “Leave A Comment” — where it’s filled in automatically — and showing it in the Sept. 18th post as well as in the usual place.
I know it wasn’t just a page refresh problem ’cause I checked — and I know the page was haunted because it showed dhogaza’s email to dhogaza just like it showed mine to me.
Anyhow, it IS gone now.
dhogaza // November 13, 2007 at 1:54 am
That fixed it, as Hank has noted.
His diagnosis appears to be correct, as my name/email boxes in the comment form are also automatically filled in (by firefox).
Hank Roberts // November 13, 2007 at 6:05 am
Firefox and autofill here too, and I do notice some other layout problems tho’ a reload fixes those (and didn’t fix the email thing).
Ah, yes, I’m sure technology’s ready to fiddle with the climate system. What could go wrong?
Julian Flood // November 13, 2007 at 9:02 am
Response to Julian Flood // Nov 12th 2007 at 8:44 pm :
[You should read this excellent writeup on the carbon cycle.
Yes, I've seen that. It was one of the things which got me digging deeper. I found an uncertainty of tens of gigatonnes in one of the 'explained' flows and it made me wonder if the human contribution could be lost in the noise. For me, the big finger pointing to A in AGW is the isotope record, not the 'we've thought of everything so what's left over must be us' hand-waves. I don't think we know the budget well enough to use that as a piece of evidence, but more research may well improve things.
[And “a study in the Gulf” isn’t a very good reference.]
http://www.holivar2006.org/abstracts/pdf/T3-032.pdf
How’s that? I find it very puzzling: why an isotope signal so early? I see the caveat that they assume steady populations of phytoplankton. I wonder if that is justified — if the population fluctuates then presumably all bets are off. And are the results reflected in other cores? Ideally I’d like to see a 200 year isotope record (organic total) in some deep sea sediments — they should give a clearer and perhaps more reliable signal, as the nutrient reduction might not occur in restricted waters with good shore mixing. Do we have a passing expert who could throw light on these matters?
Interesting how my toy theory of global warming leads me eventually to the decisive point of GW science. Even toy theories have value it seems. I would expect an increased C13 signal under the big placid deep ocean gyres, starting in about 1850.
JF
If you have the urge to buy wholesale quantities of climbing plants, BTW, the wholesale department has closed….
henry // November 13, 2007 at 1:03 pm
Some quick question, then:
Your chart shows the relationship for the past 15 years.
Any data for earlier dates?
Also, since ice cores have been used to show CO2 levels, can they distinguish between the various levels of 12 and 13?
Because, if as you say, declining levels of 13 show burning of fossil fuels, then the pre-industrial revolution levels should’t have shown much change prior to that point.
Are there natural causes to emit 13?
Hank Roberts // November 13, 2007 at 2:07 pm
This may help:
http://books.google.com/books?id=-G0WN5F2DVwC&pg=PA122&lpg=PA122&dq=heavy+isotopes+%22dead+sea%22&source=web&ots=J1upGFW2v_&sig=K3S7ft8TQyoxfjXqUwVnC52AEJg
Water entering the Gulf after it’s spent time in the the surrounding landscape would arrive already enriched naturally in heavier isotopes, compared to rainwater arising in cooler and more humid areas.
Hank Roberts // November 13, 2007 at 2:38 pm
Looking a bit longer, that link is to a poster — the published paper is behind a paywall but perhaps someone with access can comment on it:
http://www.springerlink.com/content/aj2nrb7nj80u086m/?p=ed54574c4bba46608b1630c9f4f9f325&pi=3
I’d speculate that increase in heavy isotopes began early there due to the change from forest to desert — over the past 6k years. What the real estate industry calls “improvements” happened there first.
“…before the intrusion of civilizations an almost unbroken forest flourished in the hills and mountains surrounding the Fertile Crescent… That such vast tracts of timber grew near southern Mesopotamia might seem a flight of fancy considering the present barren condition of the land …”
~John Perlin, A Forest Journey: the Role of Wood in the Developement of Civilization
found here: http://www.lichenjune.com/Elephant_Head_LAST_STAND_Forests_2.html
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