Study: plants are globally getting more efficient thanks to rising carbon dioxide

Rising CO2 leading to changes in land plant photosynthesis

Suggests that plants have achieved an optimum response to rising CO2 levels in the atmosphere


Researchers led by Scripps Institution of Oceanography at the University of California San Diego have determined that major changes in plant behavior have occurred over the past 40 years, using measurements of subtle changes in the carbon dioxide (CO2) currently found in the atmosphere.

The two main isotopes, or atomic forms, of carbon are carbon-12 (12C) and carbon-13 (13C). As CO2 has risen since the late 19th century, the ratio of 13C to 12C in atmospheric CO2 has decreased. That’s in part because the CO2 produced by the combustion of fossil fuels has a low 13C/12C ratio. There are other factors in nature as well, however, that have influenced the rate of decrease in the isotopic ratio. The measured rate of decrease in the isotopic ratio turns out to be different than what scientists previously expected.

The Scripps-led team updated the record of CO2 isotopic ratios that has been made at Scripps since 1978 using air samples collected at Hawaii’s Mauna Loa and the South Pole. The researchers confirmed that the discrepancy exists and considered several reasons for it. They concluded that no combination of factors could plausibly explain the changes in the CO2 isotopic ratio unless plant behavior was changing in a way that influences how much water plants need for growth.

The work helps to understand the details of how leaves are responding to changes in CO2. Prior to this study, it was already clear that plants behave differently when they are exposed to higher atmospheric CO2 levels because CO2 influences the behavior of stomata, the microscopic holes in leaves that allow a leaf to take up CO2. These holes also allow water to evaporate from the leaf, which must be replenished by water supplied to the roots to avoid drying out. With more CO2 in the atmosphere, a plant can afford to have smaller or fewer stomata, thus allowing more photosynthesis for the same amount of water.

But measuring exactly how much more efficient plants have become at using water has not been easy. This study provides a new method for measuring this effect, because as a leaf becomes more efficient at using water, this also influences how it takes up the different carbon isotopes in CO2. When that factor is included as a variable, the ratio of the two forms of CO2 conforms much more closely to expectations. The National Science Foundation, the Department of Energy, NASA, and the Eric and Wendy Schmidt Fund for Strategic Innovation supported the study, “Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis,” which appears in the Sept. 11 edition of the journal Proceedings of the National Academy of Sciences.

The research supports a long-standing hypothesis introduced by plant biologists, that posits plants will achieve an optimum response to rising CO2 levels in the atmosphere.

“This optimal model predicts nearly proportional scaling between water-use efficiency and CO2 itself,” said study lead author and Scripps scientist Ralph Keeling, who also maintains the internationally renowned Keeling Curve data set measuring atmospheric CO2 since 1958. “Optimal or near optimal behavior has been found in smaller studies on individual plants, but this paper is the first to show that it may be evident at the scale of the entire planet.”

The increase in the efficiency of photosynthesis documented in this study has likely helped plants offset a portion of human-induced climate change by removing more CO2 from the atmosphere than they would have otherwise.

“The full implications are still far from clear, however, and any benefits may be more than offset by other negative changes, such as heat waves and extreme weather, biodiversity loss, sea level rise, and so on,” said Keeling.


The study:

Atmospheric evidence for a global secular increase in carbon isotopic discrimination of land photosynthesis


Climate change and rising CO2 are altering the behavior of land plants in ways that influence how much biomass they produce relative to how much water they need for growth. This study shows that it is possible to detect changes occurring in plants using long-term measurements of the isotopic composition of atmospheric CO2. These measurements imply that plants have globally increased their water use efficiency at the leaf level in proportion to the rise in atmospheric CO2 over the past few decades. While the full implications remain to be explored, the results help to quantify the extent to which the biosphere has become less constrained by water stress globally.


A decrease in the 13C/12C ratio of atmospheric CO2 has been documented by direct observations since 1978 and from ice core measurements since the industrial revolution. This decrease, known as the 13C-Suess effect, is driven primarily by the input of fossil fuel-derived CO2 but is also sensitive to land and ocean carbon cycling and uptake. Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed 13C-Suess effect unless an increase has occurred in the 13C/12C isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements. We further show that the inferred discrimination increase of 0.014 ± 0.007‰ ppm−1 is largely explained by photorespiratory and mesophyll effects. This result implies that, at the global scale, land plants have regulated their stomatal conductance so as to allow the CO2 partial pressure within stomatal cavities and their intrinsic water use efficiency to increase in nearly constant proportion to the rise in atmospheric CO2concentration.


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A shocking study. Does this mean that a decrease in the CO2 content in the atmosphere causes a mass death in plants that are then accustomed to the increased content? Less roots are formed, so the plant masses that are then massier under an elevated CO2 content of the atmosphere can no longer be fed when the CO2 content decreases. One must and should also consider these consequences, even if they seem so ridiculous. Therefore it would seem desirable from a plant perspective if the CO2 content of the atmosphere were still somewhat higher. We are now setting up a union of the plant-concerned scientists. More support is required. Of course in the form of dollars. Not of Dogs.

Moderately Cross of East Anglia

So can someone just clarify this: despite stating the change in ration between 13C and 12C (which apppears to be vanishingly small) is because of fossil fuel burning, the study concludes that a combination of this and other factors still doesn’t explain the change nearly as convincingly as a change in the (respiratory?) behaviour of the plants themselves. What am I missing here?


You do not miss anything here. What is missing is contained in the requested further support for later research, which must be essential as a ritual in addition to the mention of humanized climate change in each study if it is to go through the peer review.
What this means is clear to me, Mother Nature can adapt in any situation that can occur on our planet in a very short time. It does not matter which form of CO2 is in the mix. Mother Nature also had plenty of time and opportunities to adapt to the situations and levels. What is the miserable period of our existence aginst these grandeur . The fact that the planet becomes greener is also evident from the practical experience by means of satellite recordings. I believe Mother Nature can not be brought out of balance by us. For this, an impact of an asteroid or a distance from the habitable zone of our sun would be needed. A strong impulse from the outside.


No need to go to the other extreme from the extremists. Hans-Georg .
Humans do affect the planet. Increased plant growth is one of the positive effects. That does NOT imply there are no effects or that no effects are negative.


This is not just “plants” there is a lot photosynthesis in the oceans and also the question of oceanic outgassing / absorption. It seems that once again there are too many loose variables in this equation and thus hundreds of possible solutions.
I don’t have time to study the paper in detail but it looks interesting. Ralph Keeling is a serious scientist and the Scripps gas analyses started by his father are a foundation stone of our understanding.


Greg, on longer timescales there is no effect. Absolutely nothing. Mother nature adopt us effortlessly. In shorter time scales there is any effect of mans work on earth. But this is also exaggerated by us, because we see us as the navel of the world. Good to see during Irma. This wind lady was given medial great attention, from both sides of the “Klimadebatte”. But at the same time, other major natural disasters were happening, which almost became a marginal note. And of which the planet will nevertheless recover in a short time. The man, above all the supposedly civilized in the western world, also surpasses on short time scales. We must have more humility before nature, it can obliterate us personally in a short time, but have no interest in eradicating the human kind. But it offers almost paradisiacal conditions of life even under CO2 increase, simply by triggering a mechanism, tested over millions of years, in plants. Who knows what other mechanisms there are?.

Tom in Denver

Hans, I think your missing the bigger picture here. For the past 550 million years since the Cambrian explosion of life the CO2 content in the air was between 1000 ppm and 2000 ppm for 95% of the time. THis was the time when land plants evolved. Higher CO2 content is baked into the plan DNA. It was only in the last 10s of millions of years that CO2 dropped to these extraordinary low levels, that plants had to adapt to the CO2 starvation by creating more and larger stomata. Not the other way around.
You’re temporal arrogance is showing

Old England

The first thing which occurred to me was that if plants discriminate between 13C/12C then any past atmospheric ratios derived from tree ring samples may give a false ratio of past atmospheric concentrations.
How significant might that be ?

Samuel C Cogar

if plants discriminate between 13C/12C then any past atmospheric ratios
Old England, no one actually cares about past atmospheric ratios between 13C/12C.
It is the “currently measured atmospheric ratios” between 13C/12C that the proponents of CAGW are all so excited about because their “fuzzy math” calculations and illogical reasoning has proven to them that the burning of fossil fuels by humans …… is the direct cause of said changes in the measured “atmospheric 13C/12C isotopic ratios”.
Be sure to read my other posted comment HERE .

Old England

Hi Samuel,
my thinking was that if past C12 / C13 ratios are not representative of atmospheric concentrations then there is no argument which can be made that burning fossil fuels has altered the ratios.
These ‘changed’ rations have been cited to ‘prove’ that mankind is responsible for the increases in atmospheric CO2, as opposed to increases from natural sources in a naturally warming world.
Or am I looking at this wrongly ?


OE, The plants don’t discriminate between carbon isotopes. That is, there’s no advantage or disadvantage to speak of. It’s just that the laws of physics are such that the metabolic and physical systems the plants use result in different ratios and therefore scientists can use them to help determine what the levels of CO2 actually were.

Bob boder

“OE, The plants don’t discriminate between carbon isotopes. That is, there’s no advantage or disadvantage to speak of. It’s just that the laws of physics are such that the metabolic and physical systems the plants use result in different ratios and therefore scientists can use them to help determine what the levels of CO2 actually were.”
Did you read the article?

Samuel C Cogar

if plants discriminate between 13C/12C then any past atmospheric ratios are not representative of atmospheric concentrations
Old England, the “claim” is that those C12 / C13 isotopic ratios have been a “changing” ever since the burning of fossil fuels began over 100 years ago. And their reasoning is, given their implied “fact” that the fossil fuels are “shy” on the C13 isotope is their literal proof to the CAGW’ers as to why the C12 isotope is now dominant in atmospheric CO2.
What they refuse to address is the fact that the C13 isotope is being sequestered in the limbs, trunks and roots of trees as well as in the soil at the base of the trees. And the C13 isotopes will remain sequestered therein until they are released back into the atmosphere via “oxidation” of their entity of entrapment.

Moderately Cross of East Anglia

ratio not ration

‘Study: plants are globally getting more efficient…’
And that’s inherently a good thing because….?
Pay no heed to the tacit premises behind the curtain! Bow! Bow to the Cult of Efficiency!
What we desperately need is a broad-based, grass-roots movement with the cultural licence to truly interrogate and subvert our age’s implicit, opt-out allegiance to what I call biological rationalism, a concept which has its roots in the deconstructionist response to economic rationalism, and particularly the work of Deleuze, Gaétan-Picón and Mpemba—and to do this, we don’t merely need scientists. This will require the cross-fertlization of voices from across the arts, fashion and choreography gamuts, not to mention the engagement of traditional knowledge-holders, both of color and otherwise.


… because you get more food from that same arable area, arable area increases globally and less irrigation is required to get the same output ( or more output is gained from the same available water ).
Maybe your grass roots, roots and cross-fertlization will also become more efficient ( if you don’t mind me using that Cult of Efficiency term).

David A

Brad keys, take your post normal science and please destroy it forever.
It is better because CO2 at 400 ppm vs 280 ppm allow people to grow 15% to 205 more food, on the SAME amount of land on the SAME amount of water. (Arable land and water supplies are real problems in some areas) Thus if we instantly went back to “safe” 280 ppm CO 2 levels about one billion people die, or more after all the wars.

Tom S.

“traditional knowledge-holders” seriously? Perhaps some of that “knowledge” goes back centuries but not to the high-C02 periods. You ave exceeded my daily limit of soft, pre-science input at which point I become nauseus. There are to continental USA sized land areas of new green leafs as a result of CO2 fertilization since the 1950s. As a result, millions in sub-Saharan Africa have not starved to death and foiliage has been keeping up with deforestation – effectively increasing the growth of Truffula Trees faster that we can make Thneeds (something you can probably understand).

Dave Fair

/sarc, Brad?

D. J. Hawkins

With Brad, always. It’s like that Star Trek TNG episode where the aliens could only communicate in metaphor. “Shaka, when the walls fell.” Like the aliens, it is his only form of communication.

/Sarc would imply I was finished being sarcastic.

Dave Fair

You could use: “… to be continued.”

Ah, so that’s the Fair Use Doctrine I keep hearing about

Dave Fair

No, Brad; Fair Use is mine.

Bob boder

I think you are spending too much time smoking funny weed.

and I think you’re smoking yours far too quickly.
I used to be like you: a slave to the clock, a fast-weed junkie, never taking the time to savor what Aldous Huxley called the Five Stations of Getting Wasted.
Then I got a job in Klimanürnberg, Germany, and the rest is history. They actually appreciate funnyweed here. (Dealers are more respected than teachers in many Northern European cultures.) And they grow proper funnyweed—the real stuff, not that lung-trash I used to get at Starbuck. I wouldn’t go back to smoking American funny if you paid me.
Thus began my long journey of deprogramming from the Cult of Efficiency.

Bob boder

Ok, now I just want what ever it is you are smoking.


What’s the problem with efficiency? Who doesn’t want to get more miles per gallon, or yield per acre?
Apply the theorem of limits and push it to the extreme–that of complete inefficiency. Do you think such things as computers would exist, or civilization for that matter?
In our day such “deprogramming” was epitomized by the phrase “Turn on, tune in, drop out”–a counterculture-era phrase coined by Timothy Leary in 1966.
From the Urban Dictionary:
“A term coined by Timothy Leary to describe the psychedelic experience. Leary explains it in his book Flashbacks as such
“Turn on’ meant go within to activate your neural and genetic equipment. Become sensitive to the many and various levels of consciousness and the specific triggers that engage them. Drugs were one way to accomplish this end. ‘Tune in’ meant interact harmoniously with the world around you – externalize, materialize, express your new internal perspectives. Drop out suggested an elective, selective, graceful process of detachment from involuntary or unconscious commitments. ‘Drop Out’ meant self-reliance, a discovery of one’s singularity, a commitment to mobility, choice, and change. Unhappily my explanations of this sequence of personal development were often misinterpreted to mean ‘Get stoned and abandon all constructive activity.”
“Like every great religion of the past we seek to find the divinity within and to express this revelation in a life of glorification and the worship of God. These ancient goals we define in the metaphor of the present — turn on, tune in, drop out.” – Timothy Leary
I have a nephew who began using “weed” in high school: He eventually dropped out of school, couldn’t hold a steady job, became a frequent prisoner, was married and divorced, and now we don’t even know where he is.
Personally, I’d rather stick with the Cult of Efficiency, Brad–you can have your weed and all that goes with it (or doesn’t go with it, if you catch my drift).

Geoff Pohanka

The Earth is greening according to NASA. We have record crop production. The benefits of rising CO2 are conveniently overlooked.


Some might even call it an inconvenient truth.


CO2……… the GREENING GAScomment image

Roger Knights


Chris Wright

CO2 isn’t a greenhouse gas, it’s a green gas.
This is literally true, because greenhouses don’t work by trapping radiation, they work by trapping warm air and stopping convection.
How appropriate that the AGW name is based on scientific ignorance!

Thomas Homer

Indeed …
Carbon based life forms require carbon, where does the carbon come from?
Organic matter has carbon, where does the carbon come from?
Can the Carbon Cycle of Life be completed without CO2?

Earl Jantzi

NO. The Carbon Cycle of Life CANNOT be completed without CO2.


That’s not the whole story, is it?
CO2 is not universally a good thing as regards crops even without the effects of climate change
(flash drought in Montana? Nothing to do with climate?)


Griff, what evidence do you have that anthropogenic carbon dioxide has anything whatsoever with the drought in Montana?

Bob boder

Same evidence he has for any of his statements ZERO!

Mike Maguire

I predict crop yields and production for a living based on weather and other conditions. Your links are completely full of it.
Crops in the real world where they grow, continue to outperform modeled bullshit


CO2 is higher. There’s a drought in Montana. That’s all the proof he needs.


“I predict crop yields and production for a living based on weather and other conditions. Your links are completely full of it.”
Wow, what a scientifically robust refutation of a paper.


Chris, are you being paid to double as a comic?


We have a model that says that plants don’t benefit from CO2.
We have real world evidence showing that they do.
Of course we go with the model, it’s more scientific.


Ah the random drought excuse. That is in between the flood and hurricane excuse.


Is this the same as the mega-droughts in the US a 1000 years ago?

Love that one, one of those old facts that seem to get ignored..

tom s

Wow, there’s a drought somewhere on planet earth? I forgot to plug in my Prius. Sorry Montana.


Griff, the second link is models all the way down. The first link doesn’t even make a convincing case since no actual experiments are done,here is the Summary from YOUR link you never read:
Current evidence suggests that that the concentrations of atmospheric CO2 predicted for the year 2100 will have major implications for plant physiology and growth. Under elevated CO2 most plant species show higher rates of photosynthesis, increased growth, decreased water use and lowered tissue concentrations of nitrogen and protein. Rising CO2 over the next century is likely to affect both agricultural production and food quality. The effects of elevated CO2 are not uniform; some species, particularly those that utilize the C4 variant of photosynthesis, show less of a response to elevated CO2 than do other types of plants. Rising CO2 is therefore likely to have complex effects on the growth and composition of natural plant communities.”
Doesn’t sound like a big concern to me.
Here is a website where HUNDREDS of published science papers show generally positive effects of increased CO2 in the air.
Plant Growth Database
You are terrible at this Griff!


So the authors say that plants benefit tremendously from increased CO2, but that some plants benefit more than others and because of this I latter point the (presumably net) response will be “complex”. Alright. So, the authors identify a largely academic problem but acknowledge that, pragmatically, increased CO2 is definitely good for plants and for our food supply.
If one accepts what that abstract says to be true, then one is definitely an idiot if one also believes an increase in CO2 is a net cost to society.


Griff stop Investigoogling.
In the Nature paper, the only (assumed) drawback to elevated CO2 is reduced plant protein. Note that the author of the paper, cited his own work, regarding that drawback.
The NatGeo article (using models) makes no mention of elevated CO2 being detrimental to plants.
This is why you shouldn’t Investigoogle. You start posting things you “think” they say, which they don’t.

Peta of Newark

What awful language they use here.
I take it as:
The ratio of C12 to C13 has changed (lowered) because of fossil fuel burning BUT, not as much as they expect. This is proposed to be because of Global Greening and (where I lose it) through something to do with the water the plants use.
Is it:
1. They use less water when a lot of CO2 is around?
2. They become more 12/13 selective when a lot of CO2 is around?
Is there any proof or explanation behind The Paywall for either of these?
How’s about, a lot of high ratio 12/13 carbon is coming from somewhere?
For instance, from the dirt beneath their/ours/everyone’s feet.
Soil organic carbon that is the remnants of plants that lived 100’s and even 1000’s of years ago possibly?
In the US, you’re working dirt (Great Plains/ Corn Belt) that was created under Canadian forest in the previous interglacial – 100 thousand plus years ago.
It was ‘bulldozed’ off Canadia by the Laurentide ice-sheet and dumped on what is now the corn belt.
It was up to 12 feet deep, unusual for normally created dirt which builds to only 2 feet normally.
How deep is it now – 4 inches last time I heard. So where has all ancient plant material gone if not up into the atmosphere?
It is t similar all around the globe where farming is active – usually called Soil Erosion. The depletion of soil organic carbon by repeated ploughing, cropping, exposure of bare soil to sunlight and not least – the use of nitrogen fertiliser.
We all cheer and shout hurray when NASA tell us ‘The planet is greening because of CO2″
CO2 is not a fertiliser -it is a basic staple for plants and will only affect their growth if or when it becomes their Liebig limiting nutrient.
It only does that at well below 200ppm.
They say ‘water use efficiency improves with extra CO2.
Fine. Right. Maybe.
But what they are actually saying there is that water was the limiting nutrient. At 200ppm+ plants are awash with CO2 and giving them more will have no effect.
Giving those plants some extra water would have had exactly the same effect.
(Cause and Effect go through the mincer yet again. sigh)
The thing that will cause plants to grow better is to increase their supply of what actually is their limiting nutrient.
As almost any farmer anywhere will tell you, the thing that gives the biggest bang-per-buck is nitrogen
It feeds the plant itself but especially the soil bacteria.
Again, ask the farmer why he’s reluctant to spread nitrogen in cold weather, typically soil temperatures of less than 5 degC
Simply because it doesn’t work and it doesn’t work because the soil bacteria, at less that 5 degC are effectively dormant. Like bacteria everywhere.
Why else does the fridge in your kitchen work at the temperature it does (5 degC or less).
So, soil bacteria are stimulated (fertilised) by nitrogen and this feeds the plants.
The soil bacteria are decomposing ancient plant material, producing acid that attacks the rock fraction of the dirt (this satisfies the plants’ ned for trace elements) but also, here’s the kicker, Carbon Dioxide.
CO2 that was taken in by growing plants any time inside the last 10,000 years, or in the case of the Corn Belt, the last 120,000 years.
This is what is diluting these people’s 12/13 ratio and nitrogen is the root cause (nice pun there doncha think)
And the nitrogen is coming from not just farmers, but from where almost anything is being burned.
Whether that is petrol, gasoline, diesel, kerosene, coal, natural gas or biomass.
Burn anything in a normal Earth atmosphere and you get water soluble nitrogen and it is Rocket Fuel for plants. Also anywhere where there is electrical sparking or even just (air insulated) high voltages
THAT is what’s causing Global Greening.
And, by the bacterial erosion of ancient dirt, we get rise in atmospheric CO2 and, believe it or not, that is what these muppets have actually discovered.
Remember one of the pictures from OCO satellite – it showed large amounts of CO2 over equatorial jungle and also that is where most greening is happening.
How? Why?
If CO2 was causing the greening, levels above the jungle would be lower than average, not higher because there are no human sources in the average jungle.
The jungle is greener AND the CO2 is higher because nitrogen is raining down into the jungle.
It feeds the plants certainly (hence green) but also and not least, the bacteria on the forest floor and THEY are ramping up the CO2 levels.


Very interesting. The contribution of NOx to the phenomenon does ring true.


A really cogent post. Thanks.

Ziiex Zeburz

Peta of Logic ? sounds better


This is not quite true. The cycle of photosynthesis involves inhaling and exhaling. What we see as large amounts of CO2 over jungle areas via satellites can be a product of the exhale of CO2. For this, one would have to know at which times the satellites fly exactly over the jungle. At night or during the day? In addition, we can see the effect of the Greening also in higher latitudes, not only in jungle areas in the tropics. Also in latitudes, where there is less CO2. I agree with you that the effect of fertilization with CO2 is far enough. A plant cover creates its own chemical conditions in the atmosphere to make life as comfortable as possible. This also includes the formation of aerosols, which, as we all know, can also act as fertilizers.


One more point to add to Peta’s comment: nutrients are limited by plant transpiration; that is, the movement of water through the roots, stem, and leaves ( and finally out the stomata). Slow the transpiration and you slow the rate at which nutrients get to the growing cells unless the nutrient concentration in the soil somehow is greater — a variable not measured in this study. So the point is, plant physiology is complex and pinning it down to one effect is short-sighted.

University of California San Diego, National Science Foundation, Department of Energy, NASA, you are just 35 years late in acknowledging what Sherwood Idso has been saying since 1982 with his book Carbon Dioxide: Friend or Foe? Oh well, better late than never


Thanks. I was wondering when basic greenhouse observations would show up.
What happens when you take the high growth plant out of the greenhouse and replant? Does it just slow down or is it harmed by the change.

Steve Case

Bingo, I’m out in the woos on an iPad and putting up links is chore, otherwise I would have been JOTS (Johnny On The Spot) with it.


That’s under constant water conditions, which is not the case with rising CO2.

Dave Fair

What is the measured water conditions over time, Chris?


You know that for a fact troll?
Or is it just what the models have told you to believe?
Regardless, in the last 20 years the models have told us that CO2 means more water, less water and no change in water. All at the same time.
Any who, CO2 means that plants use water more efficiently, so even if the models you are chosing to reference this time accidentally turn out to be correct, and available water does drop, it won’t matter.


Studies in the 90’s were already addressing this question of plant efficiency in response to rising CO2 concentrations. Of great interest is how the Ginkgo trees endured 270 million years of changing atmospheres. Here’s one summary.


Note that the ratio is tied to a preference in plants for the C-12 isotope. This preference causes the atmosphere to have less C-12 than other sources. Burning fossil fuel adds C-12 to the atmosphere, decreasing the C-13/C-12 ratio. However, because the atmosphere has been modified by plants and is therefore deficient in carbon-12 relative to other reservoirs of carbon, any increase in carbon content in the atmosphere should be expected to decrease the C-13/C-12 ratio. Stating that the ratio is decreasing is the same thing as stating that the carbon content is increasing. This isotope change is one of the primary pieces of evidence to show that burning of fossil fuels is the cause of the measured increase in carbon dioxide. Since all known sources of increase in atmospheric carbon dioxide will move the ratio in the same direction, it is the magnitude of the ratio change that must be tied to fossil fuel use to make the statement that burning is the cause of the change. This paper makes it clear that the ratio has not changed in the expected way if we are to attribute the increase in atmospheric CO2 to the burning of fossil fuels.

Crispin in Waterloo

Something not stated in the comments so far is that the oceans are a large reservoir of C13-poor carbon dioxide because it has been down there a long time. CO2-containing sea floor vents obviously emit less C13, and any ratio that disappears into the surface waters and emerged 800 years hence will have an altered balance as well.
For those who didn’t catch the concept of an isotopic ‘preference’ remember that bananas have a strong preference for potassium 40 – the radioactive version – not K39. So all bananas are more radioactive than other plants around them because they accumulate K40. It is very reasonable to hear than many plants prefer C12 over C13, for whatever reason.
Another possibility is that there is a mistake in the estimate of the natural carbon cycle flow volume and what the impact that human emissions from fossil fuels and land clearance have, or ought to have. Assume nothing. Examine everything. Keep an open mind.


However, this also means that our combustion of C and the formation of C-12 generally does very well for the plants. From our Wikipedia: “Plants and photosynthetic bacteria absorb carbon dioxide from the atmosphere and convert it to carbohydrates such as glucose by photosynthesis under the influence of light and absorption of water, which simultaneously releases oxygen from the decomposition of water as an energy carrier and building material for all other biochemical substances such as polysaccharides, nucleic acids and proteins, carbon dioxide is the raw material for the production of all biomass in the primary production of ecosystems.
The degradation of biomass by aerobic respiration is again associated with the formation of carbon dioxide and the consumption of oxygen, reversing the process of photosynthesis. All organisms of an ecosystem breathe continuously, while photosynthesis is linked to the availability of light. This leads to the cyclical increase and decrease of carbon dioxide in the daily and seasonal rhythm as a function of the different light intensities.”
In addition, the supply of CO2 also has other effects on plants, such as the size of the pores in leaves. Evidently, large amounts of CO2 cause a reduction in evaporation, which in turn permits a greater growth of the plant with the same amount or even less of water. But the most important is the photosynthesis cycle. Everything else like fertilization effects and water must of course be optimal. No plant, neither man stands on one leg. There are several effects that must play together. And obviously they also play together, as the greening of our planet shows.

Crispin in Waterloo

“The full implications are still far from clear, however, and any benefits may be more than offset by other negative changes, such as heat waves and extreme weather, biodiversity loss, sea level rise, and so on,” said Keeling.
For a technical scientist Dr Keeling jumps to rather a lot of speculative conclusions.

Mike Maguire

Offset by other negative changes?
What about other potential positive changes adding to it. Plants prefer warmer weather in many places. Cold is a bigger problem than heat for plants. Ask a plant if it would prefer 95 F for a few days or 15 degrees for 1 night. One brings some stress, the other kills.
Adding 4% more water vapor to the atmosphere from a 1 deg. C increase in global temperature, increases rainfall in many places. Plants also like H2O, the last time I checked.

Bob boder

So this means that it is possible that the increase in CO2 is natural and not do to man. C13 and C12 ratio has been the main reason that has been sited for evidence of the increase being all anthropogenic. So AGW may not even exist!

Samuel C Cogar

Excerpted from above noted “Abstract”, to wit:

Using updated records, we show that no plausible combination of sources and sinks of CO2 from fossil fuel, land, and oceans can explain the observed 13C-Suess effect unless an increase has occurred in the 13C/12C isotopic discrimination of land photosynthesis. A trend toward greater discrimination under higher CO2 levels is broadly consistent with tree ring studies over the past century, with field and chamber experiments, and with geological records of C3 plants at times of altered atmospheric CO2, but increasing discrimination has not previously been included in studies of long-term atmospheric 13C/12C measurements.

OH my, my, I vunder what Ferdinand E will be touting to discredit the above study results?
Last I knew, he was still passionately claiming to discredit the following as “junk science”, to wit:

Differences in altitude are also known to affect terrestrial plant carbon isotopic signatures (δ13C) in mountain regions, since plant δ13C values at high altitudes are typically enriched (Körner et al. 1988; 1991) compared to the carbon signatures of plants from low altitudes.
Soil organic matter also show enrichment in 13C with soil depth, which is suggested to be a consequence of humification and the loss of the lighter isotope (12C) via respiration, thus concentrating 13C in the soil organic matter (Kramer et al. 2003).
This might be transitional to temperature and differences in decomposition. Moreover, the isotopic carbon signatures of autochthonous and allochthonous food-sources in aquatic ecosystems are generally separated, which is also reflected in the consumer community. Stable isotope analysis is therefore a useful method for determining the autotrophic or heterotrophic character of lake food webs (Karlsson et al. 2003; 2007).”

Bob boder

Yep, been reading his arguments for years now and the only compelling point he had was the C12/C13 ratio without that bit of evidence his argument is very weak, without it there is no Anthropogenic Global Warming there is only Global Warming, so the CAGW crowd have not only lost the C in their argument now they may have lost the A as well and I am not even sure the GW has that much merit as it all may just be recovery from a GC (Global Cooling) event the LIA.

Samuel C Cogar

Right you are, Bob b,……. FE has expended a lot of time and energy creating all of those “colorful” graphics that denotes his “mismatched” 13C/12C ratios ……. and he is not going to concede to their “junk science” status without a “long-winded” verbal fight. …….. if ever. To concede “now” would surely put his reputation in question.

michael hart

The measured rate of decrease in the isotopic ratio turns out to be different than what scientists previously expected.

Just as I’ve suggested, on more than one occasion. There is no oood reason to think they’ve got it correct now either, but they still use such assumptions to make, probably incorrect, assertions about the carbon cycle.

Tom in Denver

Hans, I think your missing the bigger picture here. For the past 550 million years since the Cambrian explosion of life the CO2 content in the air was between 1000 ppm and 2000 ppm for 95% of the time. THis was the time when land plants evolved. Higher CO2 content is baked into the plant DNA. It was only in the last 10s of millions of years that CO2 dropped to these extraordinary low levels, that plants had to adapt to the CO2 starvation by creating more and larger stomata. Not the other way around.
You’re temporal arrogance is showing

tom s

“The full implications are still far from clear, however, and any benefits may be more than offset by other negative changes, such as heat waves and extreme weather, biodiversity loss, sea level rise, and so on,” said Keeling.
Um, sea level rise is variable depending on a multitude of factors, but in general shows no acceleration over centuries by and large, extreme weather as measured by a multitude of parameters is flat or down, heatwaves are actually less common today than the 1930s and so on. But I fully understand that in order to continue their funding they have to bow to the altar of Globalwarmism.

Stephen Duval

” they have to bow to the altar of Globalwarmism”
More likely, they are true believers in the Church of Climate Scientology.

Brett Keane

Reminds me of those who imagine Murry Salby never earned his Professorship.

Gary Pearse

I guess the writers of this stuff don’t think to give a short sentence on just exactly what they want the plant does re this ratio. Does the plant like 13C better than 12C? How does it select it?
Anyway I have been spouting off on this sequestration and whether climate folk were including it in their calculations. Apparently not. I’m hoping now that they have ‘discovered’ it (as they did with the importance ENSO and other oscillations that they claimed were neutral and could be ignored until convinced by sceptics of their importance) they will acknowledge photosynthesis is endothermic and the cooling effect of rapid greening also should be calculated. With a 14% increase in forest cover and fattening of existing stock this is likely to be significant. In an earlier thread I calculated 80Gt of sequestration over 10yrs, which must be too large because it equals the actual emissions, but if it is only one quarter of it, that is a lot of coal and oil to have ‘unburned’ and we should knock half a degree C off of 2100 heating calculations!


Gary Pearse
September 12, 2017 at 7:53 am
I guess the writers of this stuff don’t think to give a short sentence on just exactly what they want the plant does re this ratio. Does the plant like 13C better than 12C? How does it select it?

Well, 12CO2 weights 44 Daltons, 13CO2 weights 45 Daltons. So the average 12CO2 molecule goes a bit faster than the average 13CO2 molecule provided the temperature of the gas is remains the same. That makes 12CO2 slightly more likely to collide into RuBISCo’s active site. And if it collides more often, and with more energy, 12CO2 is more more likely to react than 13CO2. That is my understanding.
BTW, I am reading this pdf document, it might shed some light on the matter.

It was not very long ago that the ratio of C13/C12 in the atmosphere was held up by the AGW people as proof that humans were the source of the increased amt of CO2 in the atmosphere. Now, that appears to be not entirely true. Note the sniveling nod to the consensus these pathetic people called climate scientists have to make to keep their jobs while reporting information unfavorable to the consensus:
“The full implications are still far from clear, however, and any benefits may be more than offset by other negative changes, such as heat waves and extreme weather, biodiversity loss, sea level rise, and so on,” said Keeling.
Anybody who says there is no climate of fear is stupid and/or lying.

Dave Fair

It’s sad to note how far political nonsense intrudes into scientific work.


I noticed that too. But he did write “and so on”. That’s a bit tongue-in-cheek I’d say.

William Astley

Yah. It is a fact C3 type plants thrive in response to an increase in atmospheric CO2.
The C13/C12 ratio, however, is changing for non plant and non anthropogenic reasons.
The above research paper is ignoring the C13 paradox which is explained by a very large non anthropogenic source of low C13, CO2 (the source of the low C13 is deep earth CH4 which is released from the core of the earth as it solidifies which is then converted to CO2 and H2O in the upper atmosphere by UV which breaks the CH4 molecule bond and by bacteria in the oceans and by bacteria in the earth.
Changes in atmospheric C13 levels in the southern hemisphere do not support the assertion that the rise recent rise in atmospheric CO2 is due to anthropogenic CO2 emission.
C13 in the Southern Hemisphere remains the same for long periods (5 or 6 years) and then suddenly increases. As anthropogenic CO2 emission is constant C13 should if anthropogenic CO2 emission was the cause of the increase in atmospheric CO2, C13/C12 ratio should decrease gradually. That is not what is observed.
Sources and sinks of CO2 Tom Quirk

… The results suggest that El Nino and the Southern Oscillation events produce major changes in the carbon isotope ratio in the atmosphere. This does not favour the continuous increase of CO2 from the use of fossil fuels as the source of isotope ratio changes. The constancy of seasonal variations in CO2 and the lack of time delays between the hemispheres suggest that fossil fuel derived CO2 is almost totally absorbed locally in the year it is emitted. This implies that natural variability of the climate is the prime cause of increasing CO2, not the emissions of CO2 from the use of fossil fuels. ….

Figure 3. Monthly variations in 13C at the South Pole from SIO14
The correlation of changes in δ13C with ENSO events and the comparison with a simple model of a series of cascades suggest that the changes in δ13C in the atmosphere have little to do with the input of CO2 emissions from the continuous use of fossil fuels.

The other observational fact that the rise in atmospheric CO2 is not due to anthropogenic sources, is the missing and changing sink of CO2.
What is the missing sink of CO2? Why is the missing sink growing in size?

In a paper recently published in the international peer-reviewed journal Energy & Fuels, Dr. Robert H. Essenhigh (2009), Professor of Energy Conversion at The Ohio State University, addresses the residence time (RT) of anthropogenic CO2 in the air. He finds that the RT for bulk atmospheric CO2, the molecule 12CO2, is ~5 years, in good agreement with other cited sources (Segalstad, 1998), while the RT for the trace molecule 14CO2 is ~16 years. Both of these residence times are much shorter than what is claimed by the IPCC. The rising concentration of atmospheric CO2 in the last century is not consistent with supply from anthropogenic sources. Such anthropogenic sources account for less than 5% of the present atmosphere, compared to the major input/output from natural sources (~95%). Hence, anthropogenic CO2 is too small to be a significant or relevant factor in the global warming process, particularly when comparing with the far more potent greenhouse gas water vapor. The rising atmospheric CO2 is the outcome of rising temperature rather than vice versa. Correspondingly, Dr. Essenhigh concludes that the politically driven target of capture and sequestration of carbon from combustion sources would be a major and pointless waste of physical and financial resources.

Jim Ross

It has been known for a long time that the incremental atmospheric CO2 has an average δ13C of circa -13 per mil and that this is roughly half of what would be expected if it was from fossil fuel burning alone (which would be more like -26 to -28 per mil). Why does almost no-one show the data that demonstrates this fact? Good question. Could it be that the explanatory (and rather complex) models that are presented in the literature have some difficulty explaining why it reflects, on average, such a remarkably consistent δ13C content. I show the data for the South Pole below, but it is virtually the same for other measurement sites. The intercept of the linear relationship reflects the average content. It is not a fixed value over the short term, which is why I say “on average”; this is because it decreases significantly (becomes more negative) during an El Niño and increases with a La Niña. Incidentally, the underlying mathematical basis for the relationship between δ13C and 1/CO2 is sometimes referred to as the Keeling equation.
It should be kept in mind that most (all?) models seem to start with the assumption that all of the growth in atmospheric CO2 is from fossil fuels (plus land use changes), so it then has to be explained why the δ13C changes are not consistent with that assumption alone. The abstract of the posted paper would appear to suggest that these complex models are still not able to explain the observations and they need to add even more complexity, which seems to me to make it even less likely that the model is appropriate for what appears to be such a relatively simple relationship. If you want to get into the nitty gritty of all this, there is a good summary of a typical model here (see, in particular, fig. 5):
However, I prefer to start with the data. The data shown below are “seasonally adjusted” from Scripps, which means that the annual cycle has been removed. In the case of the South Pole, this is a very minor adjustment. If you are uncomfortable with this, feel free to plot the unadjusted monthly Mauna Loa data. You will get the same answer, but with a smaller R squared due to “contamination” by the annual cycle.

DeLoss McKnight

There has been little discussion about how the increased CO2 affects ocean life. I understand that 20-40% of the oxygen in our atmosphere comes from marine sources, primarily diatoms. I believe little is understood about how diatoms are affected by rising CO2. If that’s true, how can any model adjust for this ignorance? The authors of this study claim to have taken into account ocean carbon cycling and uptake, but given the lack of knowledge about diatomic response to CO2, how large is their margin of error?

Jim Ross

I completely agree. If you look at the CDIAC model, for example, which also assumes that all atmospheric CO2 growth comes from anthropogenic emissions, it concludes that ENSO has essentially no impact on net ocean-atmosphere fluxes of CO2. All of the well-known variation in CO2 growth related to ENSO is, according to their model, from the terrestrial biosphere. The view that the oceanic biosphere does not respond to ENSO with a significant variation in CO2 flux seems “rather unlikely” to me.

Jim Ross

I have now had the chance to read the full paper. In this case, they do attempt to incorporate the oceanic biosphere in their (very complex) model, but say that “we find the inclusion of a steady marine biological pump in the ocean model has very little impact”. Why would it be “steady” when we know that ENSO has a major effect on oceanic processes?
Another point which they seem to have missed is this: they averged the δ13C data from Mauna Loa and South Pole and then go chasing after an explanation for a difference between their initial model results and this average, which they say is .055 per mil per decade. What they seem to have missed is that if you simply compare the δ13C data between Mauna Loa and South Pole, there is a difference between them of .02 per mil per decade! Might be a good idea to explain that difference first.
Plus, of course, there are no plots of δ13C vs 1/CO2.

michael hart

Why would it be “steady” when we know that ENSO has a major effect on oceanic processes?

Because, like so many others, they are forced to almost admit that “without these (unreasonable) assumptions, we wouldn’t be able to get any results at all, and so have nothing to publish and won’t get paid”.
It really is that bad in some areas of science. I wish I had know that when I was younger.

Jim Ross

I think the main problem is that, having assumed that all atmospheric growth is from anthropogenic emssisions, it is then necessary to try to explain where the rest of the CO2 has gone while constrained by the actual δ13C and O2/N2 data, which then leads to ever more complex models where somewhat simpler solutions may exist. What really bugs me is the apparent reluctance to show the plots that highlight what appear to be very simple relationships, i.e. current plots of δ13C vs 1/CO2 and O2/N2 vs CO2.

Jim Ross

Oops … emissions. My previous comment (to which this correction relates) has gone into moderation, so this may appear out of sequence.

Not Chicken Little

The bottom line for me – whatever warming is taking place, for whatever reason, it appears the overall effect is good, not bad – and that rising CO2 is also good overall, not bad. I don’t view a 400+ foot rise in the oceans over the last 10-12,000 years and the melting of mile-thick glaciers coming out of an Ice Age as having been bad, nor a possible rise of 1 foot (30cm or so) at 3mm/year over the next 100 years as bad, either, even if that rise is overstated. If it gets another 1 degree C warmer in the next 150 years, as it did since the year 1850 to about 2000, much of that rise occurring when Man had little input to increasing CO2, I don’t see what’s the big deal for either sea level rise or CO2 rise – this is all supposed to be a catastrophe?
Especially after all the doom and gloom predicted for several decades now that has not come to pass. I think ordinary thinking people are realizing more and more this is all much ado about nothing, and that Man has little to no effect on natural variations in our climate – and that getting warmer and more CO2 is actually beneficial overall. A pox on all the fearmongers and data manipulators!

Stephen Duval

Here is a strong scientific indictment of Globull Warning and Unreliables

1) Every year the temperature swings about 60 degrees F. We are supposedly in a crisis because the temp rose 1.4F (.8C) over 100 years.
2) Greenland ice core data shows stable temperature for 10,000 years varying between 14-16C. The alarmist scare is based upon the thermometer temperature record that covers only 150 years or part of the current warm period that is unremarkable relative to the last 10,000 years.
3) Water vapor accounts for 75% of the greenhouse effect, CO2 for 19%. Man made CO2 emissions account for 1-2% of CO2 emissions.
4) The greenhouse effect of CO2 is exponentially reducing. From 0 to 20 ppm it is 1.5C. From 380 to 400 ppm, it is less than .05C.
5) From 1960 to today, CO2 ppm has increased steadily. From 1960 to 1980 temp decreased, from 1980 – 2000 temp increased, from 2000 – today temp has been stable.
6) Temperature predictions made by the global climate models are wrong and getting worse with every passing year.
7) Sea level increased 8 inches in the 19th and 20th century. It is likely to do the same in the 21st. Even if the Arctic melts, it is only 2% of the ice and it wont increase sea level because it is floating. Antarctica with 90% of the global ice is adding 8 inches of ice per year. During WW2 some airplanes crash landed in Greenland, recently they were found under 268 feet of ice.
8) At 280 ppm CO2, we were dangerously close to a mass extinction (plants start to die at 180 ppm). The increase in CO2 to 400 ppm has led to increased food production and the greening of the planet.