Some people claim, that there's a human to blame …

Guest Post by Willis Eschenbach

There seem to be a host of people out there who want to discuss whether humanoids are responsible for the post ~1850 rise in the amount of CO2. People seem madly passionate about this question. So I figure I’ll deal with it by employing the method I used in the 1960s to fire off dynamite shots when I was in the road-building game … light the fuse, and run like hell …

First, the data, as far as it is known. What we have to play with are several lines of evidence, some of which are solid, and some not so solid. These break into three groups: data about the atmospheric levels, data about the emissions, and data about the isotopes.

The most solid of the atmospheric data, as we have been discussing, is the Mauna Loa CO2 data. This in turn is well supported by the ice core data. Here’s what they look like for the last thousand years:

Figure 1. Mauna Loa CO2 data (orange circles), and CO2 data from 8 separate ice cores. Fuji ice core data is analyzed by two methods (wet and dry). Siple ice core data is analyzed by two different groups (Friedli et al., and Neftel et al.). You can see why Michael Mann is madly desirous of establishing the temperature hockeystick … otherwise, he has to explain the Medieval Warm Period without recourse to CO2. Photo shows the outside of the WAIS ice core drilling shed.

So here’s the battle plan:

I’m going to lay out and discuss the data and the major issues as I understand them, and tell you what I think. Then y’all can pick it all apart. Let me preface this by saying that I do think that the recent increase in CO2 levels is due to human activities.

Issue 1. The shape of the historical record.

I will start with Figure 1. As you can see, there is excellent agreement between the eight different ice cores, including the different methods and different analysts for two of the cores. There is also excellent agreement between the ice cores and the Mauna Loa data. Perhaps the agreement is coincidence. Perhaps it is conspiracy. Perhaps it is simple error. Me, I think it represents a good estimate of the historical background CO2 record.

So if you are going to believe that this is not a result of human activities, it would help to answer the question of what else might have that effect. It is not necessary to provide an alternative hypothesis if you disbelieve that humans are the cause … but it would help your case. Me, I can’t think of any obvious other explanation for that precipitous recent rise.

Issue 2. Emissions versus Atmospheric Levels and Sequestration

There are a couple of datasets that give us amounts of CO2 emissions from human activities. The first is the CDIAC emissions dataset. This gives the annual emissions (as tonnes of carbon, not CO2) separately for fossil fuel gas, liquids, and solids. It also gives the amounts for cement production and gas flaring.

The second dataset is much less accurate. It is an estimate of the emissions from changes in land use and land cover, or “LU/LC” as it is known … what is a science if it doesn’t have acronyms? The most comprehensive dataset I’ve found for this is the Houghton dataset. Here are the emissions as shown by those two datasets:

Figure 2. Anthropogenic (human-caused) emissions from fossil fuel burning and cement manufacture (blue line), land use/land cover (LU/LC) changes (white line), and the total of the two (red line).

While this is informative, and looks somewhat like the change in atmospheric CO2, we need something to compare the two directly. The magic number to do this is the number of gigatonnes (billions of tonnes, 1 * 10^9) of carbon that it takes to change the atmospheric CO2 concentration by 1 ppmv. This turns out to be 2.13 gigatonnes  of carbon (C) per 1 ppmv.

Using that relationship, we can compare emissions and atmospheric CO2 directly. Figure 3 looks at the cumulative emissions since 1850, along with the atmospheric changes (converted from ppmv to gigatonnes C). When we do so, we see an interesting relationship. Not all of the emitted CO2 ends up in the atmosphere. Some is sequestered (absorbed) by the natural systems of the earth.

Figure 3. Total emissions (fossil, cement, & LU/LC), amount remaining in the atmosphere, and amount sequestered.

Here we see that not all of the carbon that is emitted (in the form of CO2) remains in the atmosphere. Some is absorbed by some combination of the ocean, the biosphere, and the land. How are we to understand this?

To do so, we need to consider a couple of often conflated measurements. One is the residence time of CO2. This is the amount of time that the average CO2 molecule stays in the atmosphere. It can be calculated in a couple of ways, and is likely about 6–8 years.

The other measure, often confused with the first, is the half-life, or alternately the e-folding time of CO2. Suppose we put a pulse of CO2 into an atmospheric system which is at some kind of equilibrium. The pulse will slowly decay, and after a certain time, the system will return to equilibrium. This is called “exponential decay”, since a certain percentage of the excess is removed each year. The strength of the exponential decay is usually measured as the amount of time it takes for the pulse to decay to half its original value (half-life) or to 1/e (0.37) of its original value (e-folding time). The length of this decay (half-life or e-folding time) is much more difficult to calculate than the residence time. The IPCC says it is somewhere between 90 and 200 years. I say it is much less, as does Jacobson.

Now, how can we determine if it is actually the case that we are looking at exponential decay of the added CO2? One way is to compare it to what a calculated exponential decay would look like. Here’s the result, using an e-folding time of 31 years:

Figure 4. Total cumulative emissions (fossil, cement, & LU/LC), cumulative amount remaining in the atmosphere, and cumulative amount sequestered. Calculated sequestered amount (yellow line) and calculated airborne amount (black) are shown as well.

As you can see, the assumption of exponential decay fits the observed data quite well, supporting the idea that the excess atmospheric carbon is indeed from human activities.

Issue 3. 12C and 13C carbon isotopes

Carbon has a couple of natural isotopes, 12C and 13C. 12C is lighter than 13C. Plants preferentially use the lighter isotope (12C). As a result, plant derived materials (including fossil fuels) have a lower amount of 13C with respect to 12C (a lower 13C/12C ratio).

It is claimed (I have not looked very deeply into this) that since about 1850 the amount of 12C in the atmosphere has been increasing. There are several lines of evidence for this: 13C/12C ratios in tree rings, 13C/12C ratios in the ocean, and 13C/12C ratios in sponges. Together, they suggest that the cause of the post 1850 CO2 rise is fossil fuel burning.

However, there are problems with this. For example, here is a Nature article called “Problems in interpreting tree-ring δ 13C records”. The abstract says (emphasis mine):

THE stable carbon isotopic (13C/12C) record of twentieth-century tree rings has been examined1-3 for evidence of the effects of the input of isotopically lighter fossil fuel CO2 (δ 13C~-25‰ relative to the primary PDB standard4), since the onset of major fossil fuel combustion during the mid-nineteenth century, on the 13C/12C ratio of atmospheric CO2(δ 13C~-7‰), which is assimilated by trees by photosynthesis. The decline in δ13C up to 1930 observed in several series of tree-ring measurements has exceeded that anticipated from the input of fossil fuel CO2 to the atmosphere, leading to suggestions of an additional input ‰) during the late nineteenth/early twentieth century. Stuiver has suggested that a lowering of atmospheric δ 13C of 0.7‰, from 1860 to 1930 over and above that due to fossil fuel CO2 can be attributed to a net biospheric CO2 (δ 13C~-25‰) release comparable, in fact, to the total fossil fuel CO2 flux from 1850 to 1970. If information about the role of the biosphere as a source of or a sink for CO2 in the recent past can be derived from tree-ring 13C/12C data it could prove useful in evaluating the response of the whole dynamic carbon cycle to increasing input of fossil fuel CO2 and thus in predicting potential climatic change through the greenhouse effect of resultant atmospheric CO2 concentrations. I report here the trend (Fig. 1a) in whole wood δ 13C from 1883 to 1968 for tree rings of an American elm, grown in a non-forest environment at sea level in Falmouth, Cape Cod, Massachusetts (41°34’N, 70°38’W) on the northeastern coast of the US. Examination of the δ 13C trends in the light of various potential influences demonstrates the difficulty of attributing fluctuations in 13C/12C ratios to a unique cause and suggests that comparison of pre-1850 ratios with temperature records could aid resolution of perturbatory parameters in the twentieth century.

This isotopic line of argument seems like the weakest one to me. The total flux of carbon through the atmosphere is about 211 gigtonnes plus the human contribution. This means that the human contribution to the atmospheric flux ranged from ~2.7% in 1978 to 4% in 2008. During that time, the average of the 11 NOAA measuring stations value for the 13C/12C ratio decreased by -0.7 per mil.

Now, the atmosphere has ~ -7 per mil 13C/12C. Given that, for the amount of CO2 added to the atmosphere to cause a 0.7 mil drop, the added CO2 would need to have had a 13C/12C of around -60 per mil.

But fossil fuels in the current mix have a 13C/12C ration of ~ -28 per mil, only about half of that requried to make such a change. So it is clear that the fossil fuel burning is not the sole cause of the change in the atmospheric 13C/12C ratio. Note that this is the same finding as in the Nature article.

In addition, from an examination of the year-by-year changes it is obvious that there are other large scale effects on the global 13C/12C ratio. From 1984 to 1986, it increased by 0.03 per mil. From ’86 to ’89, it decreased by -0.2. And from ’89 to ’92, it didn’t change at all. Why?

However, at least the sign of the change in atmospheric 13C/12C ratio (decreasing) is in agreement with with theory that at least part of it is from anthropogenic CO2 production from fossil fuel burning.


As I said, I think that the preponderance of evidence shows that humans are the main cause of the increase in atmospheric CO2. It is unlikely that the change in CO2 is from the overall temperature increase. During the ice age to interglacial transitions, on average a change of 7°C led to a doubling of CO2. We have seen about a tenth of that change (0.7°C) since 1850, so we’d expect a CO2 change from temperature alone of only about 20 ppmv.

Given all of the issues discussed above, I say humans are responsible for the change in atmospheric CO2 … but obviously, for lots of people, YMMV. Also, please be aware that I don’t think that the change in CO2 will make any meaningful difference to the temperature, for reasons that I explain here.

So having taken a look at the data, we have finally arrived at …


1. Numbers trump assertions. If you don’t provide numbers, you won’t get much traction.

2. Ad hominems are meaningless. Saying that some scientist is funded by big oil, or is a member of Greenpeace, or is a geologist rather than an atmospheric physicist, is meaningless. What is important is whether what they say is true or not. Focus on the claims and their veracity, not on the sources of the claims. Sources mean nothing.

3. Appeals to authority are equally meaningless. Who cares what the 12-member Board of the National Academy of Sciences says? Science isn’t run by a vote … thank goodness.

4. Make your cites specific. “The IPCC says …” is useless. “Chapter 7 of the IPCC AR4 says …” is useless. Cite us chapter and verse, specify page and paragraph. I don’t want to have to dig through an entire paper or an IPCC chapter to guess at which one line you are talking about.

5. QUOTE WHAT YOU DISAGREE WITH!!! I can’t stress this enough. Far too often, people attack something that another person hasn’t said. Quote their words, the exact words you think are mistaken, so we can all see if you have understood what they are saying.

6. NO PERSONAL ATTACKS!!! Repeat after me. No personal attacks. No “only a fool would believe …”. No “Are you crazy?”. No speculation about a person’s motives. No “deniers”, no “warmists”, no “econazis”, none of the above. Play nice.

OK, countdown to mayhem in 3, 2, 1 … I’m outta here.


newest oldest most voted
Notify of

Yes, entirely reasonable. It seems most likely that human activities, not confined to fossil fuel burning, are indeed raising the CO2 ppm in the atmosphere.
It is also clear that this will contribute a modest warming effect, that is just physics.
The debate is what, if anything, happens next. Does the effect get amplified by positive feedback, or reduced by negative feedbacks, or overwhelmed by other factors.

Larry Huldén

Dear Willis!
Out of topic but text for Figure 2 includes … land use/land cover (LU/LC) changes (green line), … It looks white to me (unless I am white/green colour blind).
Good luck with your work!

Darkinbad the Brightdayler

“So if you are going to believe that this is not a result of human activities”
I’m not comfortable with the use of the words “Believe” or “Disbelieve” in a scientific context. These words are more appropriate to discussions about religion and concepts which are not open to a process of proof.
To pull them into a scientific debate is to allow participants to think and respond in a less rigorous way than they ought.


I don’t have an issue with CO2 concentrations, however regarding your first and “most solid” argument, I wonder if the ice core data has not been “calibrated” or “adjusted” deliberately to match the Mauna Loa record.


Very convincing!
Question: when drawing Fig. 4, which lifetime have you assumed for CO2?




The very flat CO2 records pre 1800 may be in part due to CO2 diffusion in ice, which potentially smooths variations that may be present during MWP, for example.
Not sure this changes any of your post-1800 arguments, tho.



Baa Humbug

Was it something we said Willis?

John Finn

So if you are going to believe that this is not a result of human activities, it would help to answer the question of what else might have that effect….
…and to bear in mind that the effect is not a ‘bump’ i.e. it’s unlikely to be not a one-off event or ‘shift’.
PS I’m not a supporter of the ‘catastrophic’ AGW argument. I’ve argued on RC with Michael Mann about the validity of his HS reconstruction, for example.

richard telford

In addition to the evidence presented above, there are at least two further lines of evidence supporting the hypothesis that the CO2 increase is caused by humans:
– the decline in atmospheric O2 concentrations, measured by Ralph Keeling’s group. See Such declines are expected if the CO2 rise is due to combustion, but not if it were due to volcanism or ocean outgassing.
– the ocean surface is on average undersaturated in CO2 and there is net uptake CO2. Hence the rise in CO2 cannot be use to ocean outgassing, or submarine volcanoes. This uptake of CO2 will cause the ocean to become more acidic (==less alkaline). See for example


I’ve never used warmist as a term of abuse. What are we meant to call people who believe the “CO2 causes warming” theory?
My only objection to being called a denier is its lack of specificness. Especially since I don’t deny that the world is warming – although I do not believe some of he claims of the rate of warming. But as a term, per se, I don’t find denier offensive.

Stephen Wilde

I’m inclined to accept that there is prima facie evidence for human activity being the cause.
However I would prefer to exclude all other possibilities before accepting that as definitive. Bear in mind that it matters not if the climate effect is negligible as seems likely for various reasons.
Areas where I have doubts are as follows:
i) How accurate are the historical methods of measurement on short timescales of say less than 500 years ? The MWP and LIA are not shown by historical CO2 records but current methods do pick up even seasonal variability at Mauna Loa. Perhaps the historical records pre 1850 are just too coarse ?
ii) Mauna Loa shows rapid seasonally related movements in the amount of CO2 recorded so the suggested 800 year lag does not seem to apply on shorter timescales.
iii) How variable is oceanic uptake in global as opposed to local terms ? Could it be that the oceans can provoke substantial changes in the atmospheric content of CO2 over certain timescales with a natural 500/1000 year cycling amounting to as much as say 50 % of the current background level ? The period 1850 to date covers a period of recovery from the LIA and the current ongoing methods of CO2 measurement show a corresponding trend but the historical methods pre 1850 show no such corresponding CO2 and temperature trends either up or down.
iv) We saw a slowdown in the CO2 upward trend in the mid 20th century when there was slight atmospheric cooling yet no corresponding changes with ongoing temperature changes appear in the historical record.
The evidence suggests a significant disjunction between the accuracy of the pre 1850 historical CO2 proxies as against post 1850 instrumental methods similar to the famous disjunction (the hockey stick) from the mid 20th century between tree ring based historical temperature proxies and the late 20th century thermometer recordings. In both cases one gets a hockey stick pattern which should not be apparent in light of what we know about the MWP and LIA from multiple other sources.
I wonder if there is also significance in both temperatures and CO2 levels being involved in tree growth. Could a similar problem with proxy methods be upsetting all of the pre 1850 non thermometer temperature records, pre 1850 CO2 and pre 1950 (that is when they seem to have started to go awry) tree growth proxies ?
There are enough questions to give doubt to the significance of the prima facie evidence of anthropogenic causation.
Certainly modern measuring methods clearly reflect a CO2 link with recent temperature changes but the proxy methods seem to lose the temperature signal altogether apart from what may be a seperate longer term signal in the form of that 800 year lag in the much older samples.

Xi Chin

I agree with you.
But there is an argument that increased temperature can cause increased CO2 levels. I am not saying the temperature has increased and that is what has caused the CO2 concentration “hockey stick”. I am asking, what is the sensitivity of CO2 concentration to temperature… i.e. what kind of temperature increased would be required to produce that change in CO2? Presumably they would be massive temperature changes? Just wondering if anyone knows the figures.
Please let me stress the hypothetical nature of my point. I do not support it as a reason for the increase in CO2. I agree that the most likely reason (and the only sensible one I know of) is anthropogenic emmissions.

I would like to give some historic context to the CO2 debate in as much according to Willis’ graph the constancy of CO2 at 280ppm but the variability of temperatures over thousands of years appears to show that CO2 is a weak climate driver.
Graph 1
The above shows reconstructed temperatures to 1400. Many periods within the LIA were surprisingly warm as well as extremely cold -all of this apparently happening with a constant level of CO2.
Graph 2 Shows the temperature diagram used in the IPCC assessment 1990 (figure 7c page 202 assessment 1) This is at the top of page.
Graph 3 The above was based on a number of graphs from Hubert Lamb (shown lower down the article linked above). The one below shows Winter severity in Europe, 1000 – 1900. Note two cold periods in the 15th and 17th centuries. Based on Lamb, 1969 / Schneider and Mass, 1975.1
Graph 4 Ice cores show constant levels of co2 on which Michael Mann based his hockey stick illustrating constant levels of temperature until the modern era. However when actual real world temperatures (CET) are graphed against total CO2 emissions we see that temperatures are not constant-in fact they are highly variable.
Graph 5 If CET data to 1659 could be extended back in time from 1300AD to around 800AD (Lamb) it would cover the Medieval Warm Period with temperature levels somewhat higher than today, but again with its peaks and troughs. The Roman optimum warm period-around 300 BC to 400AD would also show temperatures at similar levels to the MWP but again with peaks and troughs. (Few extended climatic periods are unremittingly warm or cold).
Temperatures have trended up slowly since the low point of the LIA in the 1690’s. The following link contains a graph showing CET again.
Looking at the climatic peaks and troughs illustrated in the graph stretching back from the modern era-and extending it with the various graphs through the LIA- it is a reasonable conclusion to draw that at a constant 280ppm that either CO2 is a weak climate driver, or that history has erased higher CO2 measurements that might explain those variations prior to the last half century, when our emissions are thought to be of such a significance that they are changing our climate.
This latter supposition was the approach I took in plotting a fraction of Beck’s records (shown as green dots) against CET records back to 1660 which appear on the graph linked above. Total cumulative man made CO2 emissions throughout this period are represented by the blue line along the bottom and come from CDIAC. In this respect it can be seen in context against all emissions plotted in graph 4 above.
The temperature spikes make much more sense with these additional CO2 measurement points, and bearing in mind the well documented temperatures back to Roman times and beyond-to levels greater than and less than today- it is reasonable to conclude that in as much CO2 is a contributor to the climate driver mechanism, it is as part of natural CO2 variability within the overall carbon cycle whereby nature makes a far greater contribution than man.
If there are no CO2 spikes (high and low) to match the temperature spikes (high and low) either;
a) The temperature spikes did not exist and Dr Mann is correct, or;
b) CO2 levels have had little or no effect on temperature in the past and it needs to be argued why they have suddenly become such a driving force today (despite temperatures today being unremarkable in a historic context).


‘Rules for discussion’, what a piece of work. Should be chiselled on the wall of every academic establishment everywhere. IMO.

Steve Schapel

Thank you once again, Willis, for the incredible amount of time and thought that goes into your articles, and for your clear exposition of the topic.
I guess it is an important question. If the increase of atmospheric CO2 is attributable to human activity, then it follows that it is possible for changes in human activity to reduce the rate of increase.
But of course, that is only relevant to those who think that reducing the rate of increase is important or desirable.


Okay Willis… you econo-freaka-nature you!

My brain always seems to find tangents to a topic that keep me entertained for hours. I am happy to accept that Willis has, as usual, done his homework properly and that he has made a properly reasoned and validated case for us humints being the cause of the rise of the quantity of CO2 in the atmosphere – but if CO2 is mostly plant food, is that not a GOOD THING that will help our food crops grow? And why does everyone bang on about fossil fuels? As I see it, the burning of non-fossil fuels such as dried cow dung, trees etc is also a problem due to soots etc given off, deforestation, etc.


Mr.Eschenbach, are you crazy? No, you’re not; you’ve given me a lot to think about. Thank you.

charles nelson

looks like the ‘sequestration curve’ is chasing the emissions curve. Is the difference going into oceans or biomass?

George Tetley

BOOM !!!


Is anyone seriously suggesting that the CO2 increase hasn’t, at least in part, been due to humans burning fossil fuels? Can we differentiate natural burning of fossil fuels from the data, and what contribution do they make to the overall CO2 source?

Phillip Bratby

You have Willis’ surname spelt incorrectly at the top.


Thanks for another informative post.
I really don’t care what camp someone is from, as long as their numbers add up.


Its probably me being stupid on a monday morning, but I couldn’t find a link to the actual data that the anthropogenic emissions are based on. Is there one?

Alexander Vissers

An interesting summary of atmospheric CO2 trend. Moreover the recognition of our relative ignorance on the fluctuations is putting us back on our feet. Maybe another good advice: don’t claim what you don’t know.


Sorry, meant to say – a link to the data on which the “ESTIMATIONS” of anthropogenic emissions are based on.


Another informative post.
How nice to see the mother (I’m speaking literally, of course) of all hockey sticks (Fig.1) displayed so prominently on WUWT!!!
However, with respect to your treatment of the rate of absorption of CO2 by the oceans, you say:
“Suppose we put a pulse of CO2 into an atmospheric system which is at some kind of equilibrium. The pulse will slowly decay, and after a certain time, the system will return to equilibrium.”
You suggest the rate of decay is exponential. However, for a truly exponential decay, the instantaneous rate of absorption must be proportional only to the concentration of CO2 in the atmosphere. This requires that the absorbing agent – the oceans – are unaffected by the process (ie. are essentially infinite) and hence do not affect the rate of absorption. But that is not the case.
The oceans are limited in their capacity to absorb CO2 for (at least) two reasons:
Firstly, the volume of ocean available to the atmosphere is relatively small compared to the total volume of the oceans. For CO2 to be absorbed into the bulk of the oceans, and removed from contact with the atmosphere, it needs to be absorbed in cold polar regions with downwelling currents. Elsewhere the CO2 tends to remain in the surface layers of the ocean.
Secondly, the reaction whereby CO2 is most readily absorbed is NOT by simple reaction with water, ie:
CO2 + H2O H2CO3 H+ + HCO3- 2H+ + CO3–
Rather, it is by reaction with carbonate ion (CO3–), which is itself largely derived from weathering of terrestrial rocks, and is present in limited quantities, thus:
CO2 + CO3– + H2O 2HCO3- [the HCO3- can also interact as above]
This limited amount of CO3– present in the oceans further ensures that the oceanic sink does not behave as if it is infinite, and therefore further removes the situation from that of exponential decay of atmospheric CO2.
So, what should we expect? In the early decades of a pulse of CO2 being added to the atmosphere, with a “fresh” ocean awaiting, the near exponential decay of CO2 is possible. But as the surface layers of the ocean become more saturated with CO2, its ability to absorb more CO2 declines, and the removal of CO2 from the atmosphere departs from the exponential, and becomes much slower. A number of published studies suggest that between about one fifth and one third of a pulse of CO2 would remain in the atmosphere for long periods, only being eventually removed over millennia as the slow weathering of rocks delivers more CO3– to the oceans.
[I may not be able to respond further – I have to go elsewhere]

Richard S Courtney

Thankyou for this. Perhaps now some rational debate can occur on this subject.
You have made clear that you “think that the preponderance of evidence shows that humans are the main cause of the increase in atmospheric CO2”.
But it is important to understand that there is no evidence which could be said to prove the matter.
I do not know if the cause of the increase is in part or in whole either anthropogenic or natural, but I want to know. And I am frequently offended by assertions of people that they do know. Such assertions hinder both the obtaining and the evaluation of empirical data that pertains to the issue.
But it seems that there are people who want to believe in an anthropogenic cause of the rise, so they assert that the cause must be anthropogenic. Their argument was repeatedly stated in another thread on WUWT and – as demonstration – I quote one such assertion of that type from there.
“XXXX. says:
June 5, 2010 at 4:29 pm
Dr XXXX says:
June 5, 2010 at 4:15 pm
“I think that Mauna Loa CO2 measurements are valid. However, I haven’t seen any evidence that man is responsible for the increase. Given that the fossil fuel derived percentage of atmospheric CO2, is estimated at 1-4%, is seems doubtful that burning fossil fuels is the cause of the increase.”
Since the measured annual accumulation in the atmosphere is about half the amount released into the atmosphere by fossil fuel combustion it’s impossible for it to be otherwise!”
The flaw in such assertions is that they assume the only addition of CO2 to the carbon cycle is anthropogenic. But this is not the case. The rapid changes to atmospheric CO2 concentration during each year show that the system of the carbon cycle very rapidly adjusts to seasonal changes in atmospheric CO2 concentration that are an order of magnitude greater than the anthropogenic emission each year. The anthropogenic emission is to the air, but the rapid changes in seasonal atmospheric CO2 concentration do not suggest that the system is near to saturation that would prevent the system from sequestering the anthropogenic emission from the air.
CO2 is emitted to the atmosphere from various sources and is sequestered from the atmosphere by various sinks. Hence, there is a turnover of CO2 in the atmosphere. An imbalance between the amounts emitted and sequestered will result in a change to the amount of CO2 in the atmosphere, but no subset of the emitted molecules accumulates in the atmosphere (all the molecules are subjected to the exchanges between the sources and sinks). In one of our 2005 papers
(ref. Rorsch A, Courtney RS & Thoenes D, ‘The Interaction of Climate Change and the Carbon Dioxide Cycle’ E&E v16no2 (2005) )
we used very conservative estimates that exaggerate any effect on the carbon cycle of the anthropogenic emission, and we reported:
“At present the yearly increase of the anthropogenic emissions is approximately 0.1 GtC/year. The natural fluctuation of the excess consumption (i.e. consumption processes 1 and 3 minus production processes 2 and 4) is at least 6 ppmv (which corresponds to 12 GtC) in 4 months. This is more than 100 times the yearly increase of human production, which strongly suggests that the dynamics of the natural processes here listed 1-5 can cope easily with the human production of CO2.”
The system is easily capable of sequestering all the emission (both ‘natural’ and anthropogenic).
Simply, the anthropogenic emission is observed to be so trivial a proportion of the total emission that it cannot overcome the ability of the sinks to sequester all the emission (including the anthropogenic proportion). At issue is why – according to the Mauna Loa data – the system does not sequester all the emission in each year since 1958, and our paper considered that issue.
As an aside, I address your point concerning the ice-core data because I think it is a distraction. There are two pertinent issues with the ice core results; viz. validation and interpretation.
Stomata data consistently show much higher (about 15%) and much more variable atmospheric CO2 concentration than ice core data.
(ref. e.g. Lenny L. R. Kouwenberg, Jennifer C. McElwain, Wolfram M. Kürschner, Friederike Wagner, David J. Beerling, Francis E. Mayle and Henk Visscher, ‘Stomatal frequency adjustment of four conifer species to historical changes in atmospheric CO2’ American Journal of Botany (2003) )/
A good – but one-sided – consideration of this subject in a form accessible to laymen is at
Hence, the ice-core data are shown to be wanting when validated against stomata data.
As Kouwenberg, 2005 (Laboratory of Palaeobotany and Palynology, Utrecht University, Netherlands) reported in 2005;
“Stomatal data increasingly substantiate a much more dynamic Holocene CO2 evolution than suggested by ice core data.”
It should be noted that ice core data are inherently incapable of revealing high and low atmospheric concentrations of the gases. There are several reasons for this with the most notable being that gases diffuse from regions of high concentration in unsealed firn in the decades before the ice sealed, and high values of the gas concentrations measured in the ice cores are deleted from the data sets using the assumption that high values are ‘biogenic artefacts’. The diffusion also reduces the observed rates of change to gas concentrations indicated by the ice core data. Stomata data do not suffer from these problems and indicate that the recent rates of change to atmospheric concentration of carbon dioxide have repeatedly occurred in recent millennia and during transition from the last ice age.
So, there is – at very least – adequate reason to assess the recent changes in atmospheric CO2 concentration as indicated at Mauna Loa, Barrow, etc. on the basis of the behaviour of the carbon cycle since 1958 (when measurements began at Mauna Loa).
Comparison of the recent rise in atmospheric CO2 concentration with paleo data merely provides a debate as to
(a) the validity of the ice-core data (which provides the ‘hockey stick’ graph you reproduce above)
(b) the validity of the stomata data that shows the recent rise in atmospheric CO2 concentration is similar to rises that have repeatedly happened previously.
Having said that, I copy below from the message that I posted on the other thread.
“Please note how trivial the anthropogenic emission is to the total CO2 flowing around the carbon cycle.
According to NASA estimates, the carbon in the air is less than 2% of the carbon flowing between parts of the carbon cycle. And the recent increase to the carbon in the atmosphere is less than a third of that less than 2%.
And NASA provides an estimate that the carbon in the ground as fossil fuels is 5,000 GtC and humans are transferring it to the carbon cycle at a rate of ~7 GtC per year.
In other words, the annual flow of carbon into the atmosphere from the burning of fossil fuels is less than 0.02% of the carbon flowing around the carbon cycle.
It is not obvious that so small an addition to the carbon cycle is certain to disrupt the system because no other activity in nature is so constant that it only varies by less than +/- 0.02% per year.
In one of our papers
(ref. Rorsch A, Courtney RS & Thoenes D, ‘The Interaction of Climate Change and the Carbon Dioxide Cycle’ E&E v16no2 (2005) )
we considered the most important processes in the carbon cycle to be:
1. Consumption of CO2 by photosynthesis that takes place in green plants on land. CO2 from the air and water from the soil are coupled to form carbohydrates. Oxygen is liberated. This process takes place mostly in spring and summer. A rough distinction can be made:
1a. The formation of leaves that are short lived (less than a year).
1b. The formation of tree branches and trunks, that are long lived (decades).
2. Production of CO2 by the metabolism of animals, and by the decomposition of vegetable matter by micro-organisms including those in the intestines of animals, whereby oxygen is consumed and water and CO2 (and some carbon monoxide and methane that will eventually be oxidised to CO2) are liberated. Again distinctions can be made:
2a. The decomposition of leaves, that takes place in autumn and continues well into the next winter, spring and summer.
2b. The decomposition of branches, trunks, etc. that typically has a delay of some decades after their formation.
2c. The metabolism of animals that goes on throughout the year.
3. Consumption of CO2 by absorption in cold ocean waters. Part of this is consumed by marine vegetation through photosynthesis.
4. Production of CO2 by desorption from warm ocean waters. Part of this may be the result of decomposition of organic debris.
5. Circulation of ocean waters from warm to cold zones, and vice versa, thus promoting processes 3 and 4.
6. Formation of peat from dead leaves and branches (eventually leading to lignite and coal).
7. Erosion of silicate rocks, whereby carbonates are formed and silica is liberated.
8. Precipitation of calcium carbonate in the ocean, that sinks to the bottom, together with formation of corals and shells.
9. Production of CO2 from volcanoes (by eruption and gas leakage).
10. Natural forest fires, coal seam fires and peat fires.
11. Production of CO2 by burning of vegetation (“biomass”).
12. Production of CO2 by burning of fossil fuels (and by lime kilns).
Several of these processes are rate dependant and several of them interact.
At higher air temperatures, the rates of processes 1, 2, 4 and 5 will increase and the rate of process 3 will decrease. Process 1 is strongly dependent on temperature, so its rate will vary strongly (maybe by a factor of 10) throughout the changing seasons.
The rates of processes 1, 3 and 4 are dependent on the CO2 concentration in the atmosphere. The rates of processes 1 and 3 will increase with higher CO2 concentration, but the rate of process 4 will decrease.
The rate of process 1 has a complicated dependence on the atmospheric CO2 concentration. At higher concentrations at first there will be an increase that will probably be less than linear (with an “order” <1). But after some time, when more vegetation (more biomass) has been formed, the capacity for photosynthesis will have increased, resulting in a progressive increase of the consumption rate.
Processes 1 to 5 are obviously coupled by mass balances.
Our paper assessed the steady-state situation to be an oversimplification because there are two factors that will never be “steady”:
I. The removal of CO2 from the system, or its addition to the system.
II. External factors that are not constant and may influence the process rates, such as varying solar activity.
Modeling this system is difficult because so little is known concerning the rate equations. However, some things can be stated from the empirical data.
At present the yearly increase of the anthropogenic emissions is approximately 0.1 GtC/year. The natural fluctuation of the excess consumption (i.e. consumption processes 1 and 3 minus production processes 2 and 4) is at least 6 ppmv (which corresponds to 12 GtC) in 4 months. This is more than 100 times the yearly increase of human production, which strongly suggests that the dynamics of the natural processes here listed 1-5 can cope easily with the human production of CO2.
A serious disruption of the system may be expected when the rate of increase of the anthropogenic emissions becomes larger than the natural variations of CO2. But the above data indicates this is not possible.
The accumulation rate of CO2 in the atmosphere (1.5 ppmv/year which corresponds to 3 GtC/year) is equal to almost half the human emission (6.5 GtC/year). However, this does not mean that half the human emission accumulates in the atmosphere, as is often stated. There are several other and much larger CO2 flows in and out of the atmosphere. The total CO2 flow into the atmosphere is at least 156.5 GtC/year with 150 GtC/year of this being from natural origin and 6.5 GtC/year from human origin. So, on the average, 3/156.5 = 2% of all emissions accumulate.
The above qualitative considerations suggest the carbon cycle cannot be very sensitive to relatively small disturbances such as the present anthropogenic emissions of CO2. However, the system could be quite sensitive to temperature. So, our paper considered how the carbon cycle would be disturbed if – for some reason – the temperature of the atmosphere were to rise, as it almost certainly did between 1880 and 1940 (there was an estimated average rise of 0.5 °C in average surface temperature.
Please note that the figures I use above are very conservative estimates that tend to exaggerate any effect of the anthropogenic emission.
Our paper then used attribution studies to model the system response. Those attribution studies used three different basic models to emulate the causes of the rise of CO2 concentration in the atmosphere in the twentieth century. They each assumed
(a) a significant effect of the anthropogenic emission
(b) no discernible effect of the anthropogenic emission.
Thus we assessed six models.
These numerical exercises are a caution to estimates of future changes to the atmospheric CO2 concentration. The three basic models used in these exercises each emulate different physical processes and each agrees with the observed recent rise of atmospheric CO2 concentration. They each demonstrate that the observed recent rise of atmospheric CO2 concentration may be solely a consequence of the anthropogenic emission or may be solely a result of, for example, desorption from the oceans induced by the temperature rise that preceded it. Furthermore, extrapolation using these models gives very different predictions of future atmospheric CO2 concentration whatever the cause of the recent rise in atmospheric CO2 concentration.
Each of the models in our paper matches the available empirical data without use of any ‘fiddle-factor’ such as the ‘5-year smoothing’ the UN Intergovernmental Panel on Climate Change (IPCC) uses to get its model to agree with the empirical data. Please note this:
the ‘budget’ model uses unjustifiable smoothing of the empirical data to get the model to fit the data, but each of our models fits the empirical data that is not adjusted in any way.
So, if one of the six models of our paper is adopted then there is a 5:1 probability that the choice is wrong. And other models are probably also possible. And the six models each give a different indication of future atmospheric CO2 concentration for the same future anthropogenic emission of carbon dioxide.
Data that fits all the possible causes is not evidence for the true cause.
Data that only fits the true cause would be evidence of the true cause.
But the above findings demonstrate that there is no data that only fits either an anthropogenic or a natural cause of the recent rise in atmospheric CO2 concentration.
Hence, the only factual statements that can be made on the true cause of the recent rise in atmospheric CO2 concentration are
(a) the recent rise in atmospheric CO2 concentration may have an anthropogenic cause, or a natural cause, or some combination of anthropogenic and natural causes,
(b) there is no evidence that the recent rise in atmospheric CO2 concentration has a mostly anthropogenic cause or a mostly natural cause.
Hence, using the available data it cannot be known what if any effect altering the anthropogenic emission of CO2 will have on the future atmospheric CO2 concentration. This finding agrees with the statement in Chapter 2 from Working Group 3 in the IPCC’s Third Assessment Report (2001) that says; “no systematic analysis has published on the relationship between mitigation and baseline scenarios”.”

Ben M

Are you sure the CDIAC dataset is accurate?
I thought a recent paper threw a bucket of cold water on it. (subscription req’d) (summary)

A good explanation of many things, especially the e-folding time. But I don’t agree with your calculation of the 31 year period. I think you have calculated as if each added ton of CO2 then decays exponentially back to the 1850 equilibrium level. But the sea has changed. It is no longer in equilibrium with 280 ppm CO2. Of course it has its own diffusion timescale, and lags behind the air in pCO2. You could think of the decay as being back to some level at each stage intermediate between 1850 and present.
If you apply that process to the emission curve, you’ll match the airborne fraction with a slower decay (longer time constant) where the decay has less far to go.

Just one thing puzzles me – ocean is the biggest storage of CO2. Solubility of CO2 follows the Henry’s law. There was MWP and LIA with cca 2 deg C difference. 2 deg C causes some 10% change in CO2 solubility.
Why there is no sign of MWP/LIA in the ice core CO2 data? If we consider only a surface layer with certain thickness (not the whole ocean volume) and calculate the 10% degassing, it should have been visible in the ice core record.
Today, the rate of CO2 rise plays well with SST data. El Nino is clearly visible, also La Nina and volcanic eruptions. But strange that 2007 La Nina is not visible. More, as oceans start to cool, the rate of rise stabilizes.


“As I said, I think that the preponderance of evidence shows that humans are the main cause of the increase in atmospheric CO2. ”
Ok, fine. Is there anything that would lead anyone to believe that the increase in CO2 is harmful in any way?


Re my previous post: unfortunately the equilibrium signs between the various chemical species have not shown up, making understanding of them a little difficult. Also, carbonate ion is shown with only one minus sign – it should have two.
Oh well. Those familiar with chemistry will have to make their own adjustments. Sorry about that.


I’m thinking about the rollercoaster graph of historical (temp/co2) that MR Al Gore/Gavin Smith presented.
If warmth has a restricted inpact of 20ppm since 1850? Things surely don’t add up in any aspect. And cause/effect co2/temp will still be written with question marks for a long time.
To me the work on climate science more describes how little we know, rather than how much.
There is a big potential that many science articles are right in some aspect. Spencer, Lindzen, Milkolzci, Scafetta, IPCC, Svensmark also. The big tragedy is that so much focus has been on the CO2 hype, which has certainly crippled the science.
Blaming CO2 without understanding the negative and positive feedabacks is is like eating dinner before you cooked it! CO2 is a gas for life. It’s very possible that we are increasing the chances for life on the planet by increasing CO2 turnover.
But no one is calculating the benefits.

I have added this thread- plus the previous one- to my own thread carried at air vent.
Collectively the articles/links/comments provide a huge reservoir of information on the subject. However the controversy remains as the science is not settled.
I think the comments from Richard S Courtney above warrant very close reading and I for one remain very suspicious of the ice core data after reading numerous articles on the subject.
It would be very useful to have a companion article on ice core data here at WUWT that uses the very latest research.

Good job, Willis. Takes guts to put stuff out there these days. For me, it is always curious what the facts are. Truth versus opinion: Can we distinguish the two?
While I am way out of my realm, commenting about origins of carbon dioxide, climate science or even responding to your article, I have been fully engaged in advising government and industry on environment, resource conservation, pollution prevention for over 30 years. Still scratch my head at the final priorities established and decisions made.
We have to be open to examine man’s role on the planet more holistically. Our world is much more complex than its response to any one chemical or molecule or organism present. Yet, our minds tend to fixate on the one thing that is the source and cause of all eco-problems, then seek its eradication. Governments and large institutions have become very skilled at chemical (flu organism) demonization, crisis creation and urgent-reactive solution, through the mass media. This is why I find resources such as WUWT so interesting and instructive. We are prompted to think first.
The average person, if there is such a person, is much more inquisitive and open to ideas, presentations, facts, data and its interpretation than institutions are willing to believe or want to accept. Computer simulations are illusive to them. You would have to have worked a government risk assessment, for example, to know how large an impact assumptions, rolled together, can have, especially on the decided course of action. Even then, we assume adopting no effect level standards for multiple materials equate to a clean soup.
Is the planet warming or cooling? It just makes no intuitive sense that lowly man could have such an effect on a trend that could be happening over hundreds if not thousands of years. One would have to assume earth is the solar system and universe.
Isn’t it the tornado that ripped through our yard last night that matters? Confining a massive oil leak after it happens to the smallest area? Planning and protecting for disruptive events is key to the survival of the human race. Ending fossil fuel use helps that how exactly? Oil will still leak naturally into oceans.
Like it our not, we are caretakers on this planet. Caretakers of each other and the environment we necessarily access. Our goal should always be the next generation. Otherwise, why procreate?
Before we obsess on fossil fuel combustion, we might want to examine the way we settle ourselves. If we did, we might reconsider our utilization of resources. This is not a federal government or world order level of intention, it is much more at the individual, family, or local community levels. Economic collapse is testing our response.
Personally, I have always had more faith in individual people than institutions. Those who come here, read your article today, think about the carbon dioxide and your suggested rules, might take a moment to reflect on context before they leap. Thank you.

Willis Eschenbach

Larry Huldén says:
June 7, 2010 at 1:01 am

Dear Willis!
Out of topic but text for Figure 2 includes … land use/land cover (LU/LC) changes (green line), … It looks white to me (unless I am white/green colour blind).
Good luck with your work!

Fixed, thanks.

Willis Eschenbach

Mooloo says:
June 7, 2010 at 1:36 am

I’ve never used warmist as a term of abuse. What are we meant to call people who believe the “CO2 causes warming” theory?
My only objection to being called a denier is its lack of specificness. Especially since I don’t deny that the world is warming – although I do not believe some of he claims of the rate of warming. But as a term, per se, I don’t find denier offensive.

All I know is that I have read comments from people who are offended by it. I use “AGW supporter” …

Andrew W

Of course, those nasty warmists have been trying to explain for years just how solid the evidence is that it is indeed human activity that’s causing the CO2 rise, it’s laughable that many “skeptics” are only capable of accepting the reasoning when it’s explained to them by one of the good people at WUWT.

Willis Eschenbach

Phillip Bratby says:
June 7, 2010 at 2:21 am

You have Willis’ surname spelt incorrectly at the top.

Fixed, thanks.

William Gray

Willis how do you manage it.
From Co2 science theres a graph showing the amplifacation of the seasonal Co2 cycle, with the claim that “about one fifth is due to human contributions.” And from WUWT an article stating soil fauna emit the same isotope as fossil fuels do, that being Co13,14. Please forgive me for not providing the links, sorry. Now a simple observation if I may. Plants love this isotope more so than Co2 (12), and coupled with warming has produced the current stat.

Richard S Courtney

richard telford:
At June 7, 2010 at 1:35 am you assert:
“In addition to the evidence presented above, there are at least two further lines of evidence supporting the hypothesis that the CO2 increase is caused by humans:
– the decline in atmospheric O2 concentrations, measured by Ralph Keeling’s group. See Such declines are expected if the CO2 rise is due to combustion, but not if it were due to volcanism or ocean outgassing.
– the ocean surface is on average undersaturated in CO2 and there is net uptake CO2. Hence the rise in CO2 cannot be use to ocean outgassing, or submarine volcanoes. This uptake of CO2 will cause the ocean to become more acidic (==less alkaline). See for example”
I address each of these “lines of evidence” in turn.
The cause of the O2 decline may or may not be related to the burning of fossil fuels. And the O2 decline is certainly NOT “evidence supporting the hypothesis that the CO2 increase is caused by humans”.
Both O2 and CO2 concentrations in the atmosphere are affected by biological activity (all the O2 is in the air because it is released by plants). Consumption of CO2 by photosynthesis takes place in green plants. CO2 from the air and water are coupled to form carbohydrates and O2 is liberated.
Hence, your first point merely introduces a debate about variation of the oxygen cycle and, therefore, adds confusion to discussion of the cause(s) of recent rise to atmospheric CO2 concentration.
Your point about “uptake of CO2” by the oceans cuts both ways. The great bulk of carbon flowing around the carbon cycle is in the oceans. An equilibrium state exists between the atmospheric CO2 concentration and the carbon concentration in the ocean surface layer. So, all other things being equal, if the atmospheric CO2 concentration increases then – as you say – the ocean surface layer will dissolve additional CO2 and alkalinity of the layer will reduce. However, the opposite is also true.
If the alkilinity of the ocean surface layer reduces then the equilibrium state will alter to increase the atmospheric CO2 concentration and to reduce the carbon in the ocean surface layer. The pH change required to achieve all of the recent rise in atmospheric CO2 concentration (i.e. since 1958 when measurements began at Mauna Loa) is less than 0.1 which is much, much too small for it to be detectable. And changes of this magnitude can be expected to occur.
Surface waters sink to ocean bottom, travel around the globe for ~800 years then return to ocean surface. They can be expected to dissolve S and Cl from exposure to undersea volcanism during their travels. So, the return to the surface of these waters will convey the S and Cl ions to the surface layer centuries after their exposure to the volcanism, and this could easily reduce the surface layer pH by more than 0.1. Hence, variations in undersea volcanism centuries ago could be completely responsible for the recent rise in atmospheric CO2 concentration.
Please note that the fact that these volcanic variations could be responsible for the recent rise does not mean they are responsible (which is the same logic as the fact that the anthropogenic emissions could be responsible does not mean that they are).
However, Tom Quirk observes that the geographical distribution of atmospheric carbon isotopes provides a better fit to the undersea volcanism hypothesis than to the anthropogenic hypothesis as a cause of the rise: see
There are many possible causes of the recent rise in atmospheric CO2 concentration. They each warrant investigation, and there is not sufficient evidence to champion any one of them.

William Gray

Use the LOVE

John Trigge

Thanks, Willis, for the several hours of reading and cogitation ahead.
In your ‘Anthropogenic Emission, 1850 – 2005’ graph, why are there no spikes covering the 2 World Wars? I would have expected the scales to be fine enough to show at least a noticable upward ‘blip’ given the enormous activity in fossil fuel use (and, I expect, explosives would also contribute) during these periods.
Back to reading/cogitating.

Roger Carr

Baa Humbug says: (June 7, 2010 at 1:23 am)      Was it something we said Willis?
    Nice, Barr. Needed that twist of wit to break the clasp of the furrowed brow muscles right at about that point.

William Gray

If our influence wasn’t so controversial we could use it to advantage. Ego and greed tisk tisk tisk.

Peter Miller

I am always intrigued by any discussion which involves carbon dioxide levels in the oceans, as simple maths exposes the ‘problem’ to be completely insignificant.
Volume of oceans: 1.35 billion cubic kilometres.
Human production of carbon dioxide: ~27 billion tonnes per year.
Therefore: If all humanity’s production of carbon dioxide was absorbed by the oceans, their concentration of carbon dioxide would increase by one part in 50 million per year.
However, the oceans only absorb around half our carbon dioxide production, so the actual increase (before use by marine organisms) would be one part in 100 million per year.
The present average carbon doxide levels in the ocean are ~90 parts per million. To increase this by one part per million (or less than 1%) would therefore take around 100 years. In reality, most of this carbon dioxide would be absorbed in the upper levels of the oceans.
Also of interest is that carbon dioxide makes up 15.1% of all gases absorbed in the oceans, versus 0.03% of all gases in the atmosphere.
I would suggest the oceans’ ability to absorb additional carbon dioxide is enormous, even at much higher temperatures than those prevailing today.

Britannic no-see-um

How trivial or significant is the direct additional respiratory and food production CO2 emission produced by increases in human longevity and population density since medieval times?